ORCID Profile
0000-0002-6792-2574
Current Organisation
Středoevropský technologický institut
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Analytical Chemistry | Separation Science | Analytical Chemistry not elsewhere classified | Analytical Spectrometry | Instrumental Methods (excl. Immunological and Bioassay Methods) | Analytical Chemistry Not Elsewhere Classified | Separation Science | Gene Expression | Bacteriology | Analytical Spectrometry | Electroanalytical Chemistry | Other Instrumental Methods |
ANZSRC Socio-Economic Objective (SEO)
Chemical sciences | Technological and organisational innovation | Expanding Knowledge in the Chemical Sciences | Scientific Instruments | Biological sciences
Related Links
Publications
On-capillary ion-exchange preconcentration of inorganic anions using open-tubular capillaries followed by elution with a transient isotachophoretic gradient
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/B001836H
Geometrical Alignment of Multiple Fabrication Steps for Rapid Prototyping of Microfluidic Paper-Based Analytical Devices
Publisher: American Chemical Society (ACS)
Date: 09-11-2017
DOI: 10.1021/ACS.ANALCHEM.7B03796
Abstract: Three main fabrication steps for microfluidic paper-based analytical devices (μPADs) were fully integrated with accurate geometrical alignment between the in idual steps in a simple and rapid manner. A wax printer for creating hydrophobic barriers was integrated with an inexpensive (ca. $300) electronic craft plotter/cutter for paper cutting, followed by colorimetric reagent deposition using technical pens. The principal shortcoming in the lack of accurate and precise alignment of the features created by these three in idual fabrication steps was addressed in this work by developing appropriate alignment procedures during the multistep fabrication process. The wax printing step was geometrically aligned with the following cutting and plotting (deposition) steps in a highly accurate and precise manner using optical scanning function of the plotter/cutter based on registration marks printed on the paper using the wax printer and scanned by the plotter/cutter. The accuracy and precision of alignment in a two-dimensional plane were quantified by cutting and plotting cross-shaped features and measuring their center coordinates relative to wax printed reference lines. The average accuracy along the X- and Y-axis was 0.12 and 0.16 mm for cutting and 0.19 and 0.17 mm for plotting, respectively. The potential of this approach was demonstrated by fabricating μPADs for instrument-free determination of cobalt in waters using distance-based readout, with excellent precision (%RSD = 5.7) and detection limit (LOD) of 2.5 ng and 0.5 mg/L (mass and concentration LODs, respectively).
Separation of dithiocarbamate metal complexes by micellar electrokinetic chromatography
Publisher: Royal Society of Chemistry (RSC)
Date: 1998
DOI: 10.1039/A806306K
Light-emitting diode-compatible probes for indirect detection of anions in CE
Publisher: Wiley
Date: 10-2007
Abstract: A range of compounds were evaluated as probes for the indirect detection of inorganic ions using CE and light-emitting diodes (LEDs) as the light source. Emphasis was placed on examining probes likely to absorb strongly in the UV-Vis region near 350-430 nm as compounds, which absorb at longer wavelengths tend to be bulkier and adsorb onto the capillary wall. These probes should act as a replacement for the very effective but carcinogenic probe chromate. Two probes were identified and evaluated: p-nitrophenol and 4-hydroxy-3,5-dinitrobenzoic acid. The former showed the most potential with low-mobility anions, while the later had a moderate electrophoretic mobility and was more suitable for a wider mobility range of analytes. However, neither could match the efficiencies and LOD of chromate for the separation of the fast inorganic ions such as chloride, nitrate and sulphate. Nevertheless, application of the 4-hydroxy-3,5-dinitrobenzoic acid system to the determination of oxalate in Bayer liquors showed excellent sensitivity and selectivity.
Investigation of solute-wall interactions in separation of uranium(vi) and lanthanides by capillary electrophoresis using on-capillary complexation with arsenazo iii
Publisher: Wiley
Date: 1999
DOI: 10.1002/(SICI)1520-667X(1999)11:1<1::AID-MCS1>3.0.CO;2-U
Evaluation of capillary ion exchange stationary phase coating distribution and stability using radial capillary column contactless conductivity detection
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B606942H
Abstract: The use of radial (across) capillary column capacitively coupled contactless conductivity detection is demonstrated as a simple and rapid technique for visualisation of stationary phase longitudinal coverage and coating stability in capillary ion exchange chromatography.
Low-tech vs. high-tech approaches in μPADs as a result of contrasting needs and capabilities of developed and developing countries focusing on diagnostics and point-of-care testing
Publisher: Elsevier BV
Date: 2024
Optimisation of probe concentration in indirect photometric detection in capillary electrophoresis using highly absorbing dyes
Publisher: Wiley
Date: 2002
DOI: 10.1002/1522-2683(200201)23:1<43::AID-ELPS43>3.0.CO;2-R
Sensitive indirect photometric detection of inorganic and small organic anions by capillary electrophoresis using Orange G as a probe ion
Publisher: Wiley
Date: 02-2003
Abstract: This study addresses the two major problems in the use of dyes as highly absorbing probes for indirect photometric detection in capillary electrophoresis (CE). First, effective electroosmotic flow (EOF) modification or suppression to allow separation and detection of a wide mobility range of analytes is not straightforward when electrolytes containing increased dye concentrations are used. The suppression of EOF to less than + 5x10(-9) m(2)V(-1)s(-1) was achieved with a combination of a poly(ethylenimine) (PEI)-coated capillary and the addition of the neutral polymer hydroxypropylmethylcellulose (HPMC) to the background electrolyte. Second, the deterioration of baselines due to adsorption of the dye probe to the capillary wall is generally a problem. In this work, baseline quality at higher probe concentrations was significantly improved by a rather unusual but highly effective combination of a simultaneous application of a slight overpressure (25 mbar) at the injection end during the separation, and the use of a relatively narrow capillary of 50 microm inner diameter. Both measures would appear to be counterproductive. Optimisation of the probe concentration with regard to signal-to-noise ratio resulted in an electrolyte of 4 mM Orange G, 0.05% HPMC buffered at pH 7.7 by the addition of 10.0 mM histidine isoelectric buffer. Very high separation efficiencies of 128 000-297 000 plates were made possible by the relatively high probe concentration. Combined with excellent detection sensitivity, even with the introduction of hydrodynamic flow and a reduced optical path length, these measures resulted in limits of detection ranging from 0.216 to 0.912 microM with a deuterium l light source (248 nm) and from 0.147 to 0.834 microM with a 476 nm blue light-emitting diode (LED) light source. Reproducibility over 30 consecutive runs without changing the electrolyte was excellent, with relative standard deviation (RSD) values of 0.14-0.80% for migration time, 1.27-3.36% for peak area and 0.88-5.12% for peak heights. The optimised electrolyte was used for the analysis of inorganic anions in air filter s les, providing good agreement with results obtained by ion chromatography.
Capillary electrophoretic study of interactions of metal ions with crown ethers, a sulfated β-cyclodextrin, and zwitterionic buffers present as additives in the background electrolyte
Publisher: Wiley
Date: 06-2002
DOI: 10.1002/1522-2683(200206)23:12<1796::AID-ELPS1796>3.0.CO;2-U
Determination of metal ions by capillary electrophoresis
Publisher: Wiley
Date: 1997
Abstract: The increasing use of capillary electrophoresis (CE) in all areas of analytical chemistry has been reflected in the appearance since 1990 of significant numbers of fundamental studies and applications of CE in the area of separations of metal ions. In this article all aspects of separations of metal ions by CE are reviewed and discussed, including general concepts and approaches, s le introduction, complex formation and s le stacking, separation selectivity, the role of kinetics, capillary wall chemistry, detection techniques, method validation, and applications to metal determinations in various matrices.
Numerical model for light propagation and light intensity distribution inside coated fused silica capillaries
Publisher: Elsevier BV
Date: 07-2011
Miniature and fully portable gradient capillary liquid chromatograph
Publisher: Elsevier BV
Date: 03-2020
Ion-Exchange Based Immobilization of Chromogenic Reagents on Microfluidic Paper Analytical Devices
Publisher: American Chemical Society (ACS)
Date: 05-06-2019
DOI: 10.1021/ACS.ANALCHEM.9B01288
Abstract: Distance-based detection methods, as used in development of microfluidic paper analytical devices (μPADs), rely on the dynamic formation of a colored band along the length of the paper microfluidic channels. The color change is driven by the reaction of chromogenic reagents (typically water-insoluble) that are bound to the paper, thus not subject to being washed away by the s le flow along the detection channel. Here, we introduce the use of an anion-exchange filter paper (as a replacement for standard, unmodified filter paper) for distance-based detection in μPADs, in order to immobilize the water-soluble anionic reagents upon the paper detection channels based on ion-exchange interactions of the oppositely charged paper (protonated tertiary amine groups) and the anionic groups of the reagents. The ion-exchange (IE) paper was initially characterized and its properties were compared with standard cellulose paper. The IE paper was shown to be capable of strong retention of anionic reagents exhibiting acidic functional groups (carboxylic, sulfonic), which become deprotonated and negatively charged when in contact with the IE paper. The effect of the ionic strength (10-250 mM Cl
Separation of niobium(V) and tantalum(V) as ternary complexes with citrate and metallochromic ligands by capillary electrophoresis
Publisher: Elsevier BV
Date: 05-2001
Decomposition of Cisplatin in Aqueous Solutions Containing Chlorides by Ultrasonic Energy and Light
Publisher: Elsevier BV
Date: 06-1994
Abstract: Decomposition of cisplatin in an aqueous 0.15 M chloride solution by diffuse daylight, by monochromatic light, and by ultrasonic energy was studied using a new HPLC method. The relative sensitivity of cisplatin to light copies the curve of the absorption spectrum of cisplatin with maximum at ca. 300 nm however, any light below 500 nm must be avoided. Sonication also leads to a rapid decomposition of cisplatin. Irradiation by diffuse daylight or sonication of the cisplatin solutions for 5 min leads to ca. 1% amminetrichloroplatinate(II). Using HPLC analysis with diode-array spectrophotometric detection, the main decomposition product was identified as amminetrichloroplatinate(II).
Determination of niobium(V) and tantalum(V) as 4-(2-pyridylazo)resorcinol-citrate ternary complexes in geological materials by ion-interaction reversed-phase high-performance liquid chromatography
Publisher: Elsevier BV
Date: 07-1999
DOI: 10.1016/S0021-9673(99)00143-0
Abstract: A method for the simultaneous separation and determination of Nb(V) and Ta(V) as ternary complexes formed with 4-(2-pyridylazo)resorcinol (PAR) and citrate was developed using ion-interaction reversed-phase high-performance liquid chromatography on a C18 column. Method parameters, such as pre-column complex formation conditions and composition of the complexes were investigated using spectrophotometry and HPLC. Under the optimum conditions, the Nb(V) and Ta(V) complexes were eluted within 12 min with a mobile phase of methanol-water (32:68, v/v) containing 5 mM acetate, 5 mM TBABr and 5 mM citrate buffer at pH 6.5, with detection at 540 nm. A typical separation efficiency was 33,000 and 20,000 theoretical plates per metre for Nb(V) and Ta(V), respectively. The relative standard deviation of retention times for the Nb(V) and Ta(V) complexes were 0.16% and 0.17% and for peak areas were 0.28% and 1.36%, respectively. The detection limits (signal-to-noise ratio = 3) for Nb(V) and Ta(V) were 0.4 ppb and 1.4 ppb, respectively. Results obtained for standard reference rock s les agreed well with certified values and results obtained by inductively coupled plasma MS.
Electro-osmotic and pressure-driven flow properties of frits for packed column capillary electrochromatography prepared from functionalised and bare silica packings
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/A908102J
Separation of opiate alkaloids by electrokinetic chromatography with sulfated-cyclodextrin as a pseudo-stationary phase
Publisher: Elsevier BV
Date: 2003
DOI: 10.1016/S0021-9673(02)01393-6
Abstract: The separation of six related opiate alkaloids (morphine, thebaine, 10-hydroxythebaine, codeine, oripavine and laudanine) was studied using sulfated-cyclodextrin (s-CD) as a cation-exchange pseudo-stationary phase. Cation-exchange interactions between the cationic analytes and the anionic s-CD (7-11 mol of sulfate groups per mole CD) were found to bethe predominant mechanism, allowing the separations to be performed at low pH where the opiates are protonated and exhibit very similar mobilities. The concentrations of the s-CD and the competing ion (Na+ or Mg2+) in the electrolyte were used to govern the extent of the ion-exchange interactions. Interactions with the sulfated-cyclodextrin differed for each analyte, with oripavine exhibiting the strongest interaction and 10-thebaine and laudanine showing the weakest interactions. Despite the very similar structures of the analytes, these differences resulted in significant changes in separation selectivity. The separation was modelled using a migration equation derived from first principles and based on ion-exchange interactions between the s-CD and the opiates. Constants within the model were obtained by non-linear regression using a small subset of experimentally determined migration times. These constants related to the ion-exchange affinities of the s-CD for the various opiates. When the model was used to predict migration times under other experimental conditions, a very good correlation was obtained between observed and predicted mobilities (r2=0.996). Optimisation of the system was performed using the normalised resolution product and minimum resolution criteria and this process provided two optimised separations, each exhibiting a different separation selectivity.
On-capillary ion-exchange preconcentration of inorganic anions in open-tubular capillary electrochromatography with elution using transient-isotachophoretic gradients. 2. Characterization of the isotachophoretic gradient
Publisher: American Chemical Society (ACS)
Date: 12-01-2001
DOI: 10.1021/AC0010577
Abstract: Diffuse transient-isotachophoretic boundaries can be used as an elution gradient of increasing eluotropic strength to elute inorganic anions that have been preconcentrated on an open-tubular ion-exchange stationary phase prior to electrophoretic separation. The generation and characteristics of these gradients for elution after preconcentration have been investigated. The gradients are generated by placing a low-mobility, weak ion-exchange competing anion in the capillary (weak electrolyte, WE), and a high-mobility, strong ion-exchange competing anion in the electrolyte vials (strong electrolyte, SE). Application of voltage establishes a diffuse boundary with the composition changing from the weak anion to the strong anion. Comparison of elution gradients generated with different electrolyte systems was accomplished by comparing the eluotropic strength (a function of eluent concentration, ion-exchange selectivity coefficient, and charge) and the shape of the profile as it changes from WE to SE. The ion-exchange selectivity coefficient of the SE competing anion is important in establishing a sharp change in elution strength. A large difference in mobility between the WE and SE competing anions gives an SE with a higher final eluotropic strength, but the slope of the gradient is shallower. This results in a reduction in the efficiency of analyte focusing. To ensure maximum focusing efficiency, the WE and SE electrolytes should be selected such that the SE has the highest possible eluotropic strength for a given concentration of WE. The SE competing anion should also have a sufficiently low electrophoretic mobility to ensure focusing for the maximum number of analytes, and the mobility difference between the WE and SE competing anions should be as small as possible.
Separation of organic and inorganic arsenic species by capillary electrophoresis using direct spectrophotometric detection
Publisher: Wiley
Date: 08-2002
DOI: 10.1002/1522-2683(200208)23:15<2430::AID-ELPS2430>3.0.CO;2-F
Design of background electrolytes for indirect detection of anions by capillary electrophoresis
Publisher: Elsevier BV
Date: 2000
Manipulation of separation selectivity for alkali metals and ammonium in ion-exchange capillary electrochromatography using a suspension of cation exchange particles in the electrolyte as a pseudostationary phase
Publisher: Wiley
Date: 07-1999
DOI: 10.1002/(SICI)1522-2683(19990701)20:10<1987::AID-ELPS1987>3.0.CO;2-K
Isotachophoresis on a chip with indirect fluorescence detection as a field deployable system for analysis of carboxylic acids
Publisher: Wiley
Date: 12-10-2012
Abstract: ITP with indirect fluorescence detection (IFD) was introduced three decades ago. Despite this fact, the method has never become widely adopted. The main aim of this work was to utilize the ITP-IFD for the separation of carboxylic acids by using a commercially available, portable, microfluidic chip electrophoresis system. On the 16.8-mm effective length separation channel, a maximum of eight carboxylic acids could be separated, with LOD values in a range from 0.12 to 0.4 mM. The commercial chips used for all experiments have multichannel structures important for analysis of more than one s le per a chip in case of standard use. This multichannel structure was used to investigate the possibility of multiple s le loading for ITP separation. Application of ITP-IFD was investigated for analysis of benzoate in diet soft drinks and the results were in good agreement with results of a CE method.
Role of ligand purity in separations of alkaline earth metals as arsenazo I complexes by capillary zone electrophoresis
Publisher: Elsevier BV
Date: 1998
Fluctuations in anti‐Müllerian hormone levels throughout the menstrual cycle parallel fluctuations in the antral follicle count: a cohort study
Publisher: Wiley
Date: 03-04-2016
DOI: 10.1111/AOGS.12886
Abstract: In this prospective cohort study we aimed to investigate the hypothesis that fluctuations in anti-Müllerian hormone levels stem from fluctuations in the number of antral follicles. Repeated measurements of anti-Müllerian hormone and antral follicles (follicles 2-8 mm) were performed in 44 women with a regular cycle, during one menstrual cycle. If our hypothesis that anti-Müllerian hormone fluctuations stem from fluctuations in the antral follicles is correct, a fluctuation in the antral follicles would result in an equal and parallel shift in anti-Müllerian hormone. Hence, the difference between antral follicles and anti-Müllerian hormone would remain constant over time. A mixed model analysis, assessing the stability between anti-Müllerian hormone and antral follicles, was performed using the difference between log antral follicles and log anti-Müllerian hormone. Cohen's D was calculated for the largest of fixed effects in order to assess stability in relative distance between antral follicles and anti-Müllerian hormone. To assess if fluctuation in anti-Müllerian hormone or antral follicles originated from between-subject fluctuation, or from within subject fluctuation, the intra-class correlation coefficient was calculated. Mixed model analysis and Cohen's D (0.12) confirmed the stability of the difference between log antral follicles and log anti-Müllerian hormone and so confirmed our hypothesis. The good intra-class correlation coefficient (0.73) indicated a small contribution of within-subject variation to anti-Müllerian hormone fluctuations. Fluctuations in anti-Müllerian hormone levels parallel fluctuations in antral follicles, suggesting that anti-Müllerian hormone levels are closely linked to variation in the antral follicles. This knowledge adds to the basic understanding of the origin of anti-Müllerian hormone and could aid in interpretation of in idual anti-Müllerian hormone levels.
Surface-area expansion with monolithic open tubular columns
Publisher: Elsevier BV
Date: 04-2015
Buffered Chromate Electrolytes for Separation and Indirect Absorbance Detection of Inorganic Anions in Capillary Electrophoresis
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A706001G
Short-sweep capillary electrophoresis with a selective zinc fluorescence imaging reagent FluoZin-3 for determination of free and metalothionein-2a-bound Zn2+ ions
Publisher: Elsevier BV
Date: 08-2018
DOI: 10.1016/J.ACA.2018.02.008
Abstract: A capillary electrophoretic (CE) method using a short-sweep approach and laser-induced fluorescence (LIF) detection (ShortSweepCE-LIF) was developed for determination of Zn
Portable capillary-based (non-chip) capillary electrophoresis
Publisher: Elsevier BV
Date: 04-2010
Measurement of thiol-containing amino acids and phytochelatin (PC2) via capillary electrophoresis with laser-induced fluorescence detection
Publisher: Wiley
Date: 2002
DOI: 10.1002/1522-2683(200201)23:1<81::AID-ELPS81>3.0.CO;2-V
Photochromic spiropyran monolithic polymers: Molecular photo-controllable electroosmotic pumps for micro-fluidic devices
Publisher: Elsevier BV
Date: 07-2010
New isoelectric buffers for capillary electrophoresis: N-carboxymethylated polyethyleneimine as a macromolecular isoelectric buffer
Publisher: Royal Society of Chemistry (RSC)
Date: 2001
DOI: 10.1039/B100608H
Abstract: Isoelectric buffers are attractive for electrophoresis because of their low conductivity, and their compatibility with indirect photometric detection in capillary electrophoresis (CE) where they do not interfere with the detection by exhibiting competitive displacement of the UV-absorbing probe ion. N-carboxymethylated polyethyleneimine (CMPEI) was prepared by introducing a half molar equivalent of carboxylate groups onto a polyethyleneimine backbone. Its isoelectric point determined by conductometric titration and from the pH of its dilute aqueous solution is approx. 6.8, which allows isoelectric buffering at a lower pH compared to histidine (pI7.7). Although the isoelectric point is somewhat diffuse, as expected for a polymeric compound, it exhibits a buffering capacity at a pI point of about twice that of histidine. Studies of electroosmotic flow (EOF) profile at various pH values in fused silica capillaries showed that CMPEI adsorbs onto the fused silica wall and reverses the EOF at pH < 6.5. CMPEI was applied as a buffer in an electrolyte containing 0.5 mM of the anionic dye tartrazine used as the probe for indirect detection of anions. The separation system exhibited a stable baseline, no system peaks, separation efficiencies of up to 195,000 theoretical plates, and detection limits down to 0.2 microM or 2 amol of injected analyte.
Design and performance of a light‐emitting diode detector compatible with a commercial capillary electrophoresis instrument
Publisher: Wiley
Date: 10-2004
Abstract: Indirect photometric detection in capillary electrophoresis (CE) has been predominantly performed in the UV region, in part due to a lack of suitable high‐intensity and low‐noise light sources in the visible spectral region. A new photometric detector based on light‐emitting diodes (LEDs) as light sources and compatible with a commercially available CE instrument has been designed and constructed and its performance evaluated. The utility of this detector was successfully demonstrated by the indirect photometric detection of anions using a dye as probe and absorbance measured in the visible region. The detector exhibited very low baseline noise (around 0.03 mAU), stable output, and improved upper limit of detection linearity (502 mAU) compared with previously used LED detectors. The detector was tested for indirect detection of anions separated with an electrolyte containing 4 m M Orange G as the indirect detection probe, 10 m M histidine as an isoelectric buffer, and 0.05% hydroxypropylmethylcellulose to suppress the electroosmotic flow. Extremely low detection limits were obtained ranging from 0.16–0.36 μ M (excluding chloride 0.56 μ M ), with separation efficiencies in the range of 154 000–274 000 theoretical plates.
Photoreversible ion-binding using spiropyran modified silica microbeads
Publisher: Inderscience Publishers
Date: 2010
Rapid capillary electrophoretic method for trace chromium speciation using a zwitterionic isoelectric polymer coated capillary and photodiode array detection
Publisher: Informa UK Limited
Date: 27-12-2004
DOI: 10.1081/AL-200032011
Contactless conductivity detection of synthetic polymers in non-aqueous size-exclusion electrokinetic chromatography
Publisher: Elsevier BV
Date: 03-2005
DOI: 10.1016/J.CHROMA.2004.11.081
Abstract: A capacitively coupled contactless conductivity detection (CCD) system has been applied for the detection of neutral synthetic polymers in capillary size-exclusion electrokinetic chromatography (SEEC). Polystyrene standards, that were used as a model compounds, were separated on a capillary column packed with porous 10 microm silica particles with an electrokinetically driven mobile phase, and detected by CCD and UV detection simultaneously. Mass-calibration curves for polystyrene were constructed. Satisfactory results were obtained for the linearity, the run-to-run repeatability (<0.2% for the relative retention and <4% for the peak area) and the robustness of the detector. One of the major issues in this preliminary study was to investigate the origin of the peaks observed for the polystyrene standards. The effect of the molar mass of the polystyrenes on the sensitivity was small. Therefore, the signals obtained could not be explained as the result of an increased viscosity and a decreased solution conductivity of the solute zone. An alternative hypothesis is suggested, and recommendations for further research are given.
Internal electrolyte temperatures for polymer and fused-silica capillaries used in capillary electrophoresis
Publisher: Wiley
Date: 11-2005
Abstract: Polymers are important as materials for manufacturing microfluidic devices for electrodriven separations, in which Joule heating is an unavoidable phenomenon. Heating effects were investigated in polymer capillaries using a CE setup. This study is the first step toward the longer-term objective of the study of heating effects occurring in polymeric microfluidic devices. The thermal conductivity of polymers is much smaller than that of fused silica (FS), resulting in less efficient dissipation of heat in polymeric capillaries. This study used conductance measurements as a temperature probe to determine the mean electrolyte temperatures in CE capillaries of different materials. Values for mean electrolyte temperatures in capillaries made of New Generation FluoroPolymer (NGFP), poly-(methylmethacrylate) (PMMA), and poly(ether ether ketone) (PEEK) capillaries were compared with those obtained for FS capillaries. Extrapolation of plots of conductance versus power per unit length (P/L) to zero power was used to obtain conductance values free of Joule heating effects. The ratio of the measured conductance values at different power levels to the conductance at zero power was used to determine the mean temperature of the electrolyte. For each type of capillary material, it was found that the average increase in the mean temperature of the electrolyte (DeltaT(Mean)) was directly proportional to P/L and inversely proportional to the thermal conductivity (lambda) of the capillary material. At 7.5 W/m, values for DeltaT(Mean) for NGFP, PMMA, and PEEK were determined to be 36.6, 33.8, and 30.7 degrees C, respectively. Under identical conditions, DeltaT(Mean) for FS capillaries was 20.4 degrees C.
On-line simultaneous and rapid separation of anions and cations from a single sample using dual-capillary sequential injection-capillary electrophoresis
Publisher: Elsevier BV
Date: 06-2013
DOI: 10.1016/J.ACA.2013.03.027
Abstract: A novel capillary electrophoresis (CE) approach has been developed for the simultaneous rapid separation and identification of common environmental inorganic anions and cations from a single s le injection. The method utilised a sequential injection-capillary electrophoresis instrument (SI-CE) with capacitively-coupled contactless conductivity detection (C(4)D) constructed in-house from commercial-off-the-shelf components. Oppositely charged analytes from a single s le plug were simultaneously injected electrokinetically onto two separate capillaries for independent separation and detection. Injection was automated and may occur from a syringe or be directly coupled to an external source in a continuous manner. Software control enabled high s le throughput (17 runs per hour for the target analyte set) and the inclusion of an isolation valve allowed the separation capillaries to be flushed, increasing throughput by removing slow migrating species as well as improving repeatability. Various environmental and industrial s les (subjected only to filtering) were analysed in the laboratory with a 3 min analysis time which allowed the separation of 23 inorganic and small organic anions and cations. Finally, the system was applied to an extended automated analysis of Hobart Southern Water tap water for a period of 48 h. The overall repeatability of the migration times of a 14 analyte standard s le was less than 0.74% under laboratory conditions. LODs ranged from 5 to 61 μg L(-1). The combination of automation, high confidence of peak identification, and low limits of detection make this a useful system for the simultaneous identification of a range of common inorganic anions and cations for discrete or continuous monitoring applications.
3D printed LED based on-capillary detector housing with integrated slit
Publisher: Elsevier BV
Date: 05-2017
DOI: 10.1016/J.ACA.2017.02.020
Abstract: A 3D printed photometric detector body with integrated slit was fabricated to position a LED and photodiode either side of capillary tubing using a fused deposition modelling (FDM) printer. To make this approach suitable for capillaries down to 50 μm i.d. the dimension of the in-built slit is the critical element of the printed housing. The spatial orientation of the model for printing was found to significantly impact on the resolution of the structures and voids that can be printed. By designing a housing with a slit positioned in the XY plane in parallel with the print direction, the narrowest void (slit) that could be printed was 70 μm. The potential use of the 3D printed slit for photometric detection was characterised using tubing and capillary from 500 down to 50 μm i.d, demonstrating a linear response from 632 to 40 mAU. The effective pathlength and stray light varied from 383 to 22 μm and 3.8% - 50% for 500- 50 μm i.d tubing and capillary. The use of a V-shaped alignment feature allowed for easy and reliable positioning of the tubing inside the detector, as demonstrated by a RSD of 1.9% (n = 10) in peak height when repositioning the tubing between measurements using flow injection analysis (FIA). The performance of the 3D printed housing and 70 μm slit was benchmarked against a commercially available interface using the CE separation of Zn
Speciation of arsenic and selenium by capillary electrophoresis
Publisher: Elsevier BV
Date: 06-2004
DOI: 10.1016/J.CHROMA.2004.03.045
Abstract: Capillary electrophoresis (CE) with direct UV detection, both on-capillary and with a high-sensitivity detection cell (HSDC), were used for the simultaneous determination of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), selenate [Se(VI)], selenite [Se(IV)], selenocystine (SeC), selenomethionine (SeM) and selenocystamine (SeCM). These anionic and cationic species were separated with negative separation voltage polarity in a capillary coated with poly(diallydimethylammonium chloride) (PDDAC). The background electrolyte (BGE) providing optimal separation was 15 mM phosphate buffer at pH 10.6. Arsenic and selenium species were detected at 195 and 200 nm, respectively. The limit of detection (LOD) values with on-capillary detection (75 microm i.d.) for the in idual analytes were 1.02, 1.50, 1.08, 1.35, 19.5, 0.36, 0.32, 1.11 and 1.47 mg/L, respectively (expressed as arsenic or selenium). The method precision for peak area was from 2.1 to 3.4% relative standard deviation. HSDC was applied to increase the detection sensitivity and gave LOD improvement factors from 4.7 to 8.2, yielding LODs for the in idual target analytes ranging from 0.049 to 2.38 mg/L. When the normal s le stacking mode was employed using a s le plug up to 4.6% of capillary volume, both the cationic and anionic analytes were stacked simultaneously with LOD improvement factors of 2.6-4.5 yielding LODs for the in idual analytes ranging from 0.11 to 7.42 mg/L. The method was applied for the speciation of arsenic in sediment and determination of SeM in a selenium nutrition supplement. The achieved separation selectivity also gives the method a more general application potential for simultaneous arsenic and selenium speciation when hyphenated with inductively coupled plasma MS.
Capillary electrophoresis with end-capillary potentiometric detection using a copper electrode
Publisher: Wiley
Date: 08-1999
DOI: 10.1002/(SICI)1522-2683(19990801)20:12<2539::AID-ELPS2539>3.0.CO;2-0
Combined contactless conductometric, photometric, and fluorimetric single point detector for capillary separation methods
Publisher: American Chemical Society (ACS)
Date: 04-12-2010
DOI: 10.1021/AC902376V
Abstract: This work for the first time combines three on-capillary detection methods, namely, capacitively coupled contactless conductometric (C(4)D), photometric (PD), and fluorimetric (FD), in a single (identical) point of detection cell, allowing concurrent measurements at a single point of detection for use in capillary electrophoresis, capillary electrochromatography, and capillary/nanoliquid chromatography. The novel design is based on a standard 6.3 mm i.d. fiber-optic SMA adapter with a drilled opening for the separation capillary to go through, to which two concentrically positioned C(4)D detection electrodes with a detection gap of 7 mm were added on each side acting simultaneously as capillary guides. The optical fibers in the SMA adapter were used for the photometric signal (absorbance), and another optical fiber at a 45 degrees angle to the capillary was applied to collect the emitted light for FD. Light emitting diodes (255 and 470 nm) were used as light sources for the PD and FD detection modes. LOD values were determined under flow-injection conditions to exclude any stacking effects: For the 470 nm LED limits of detection (LODs) for FD and PD were for fluorescein (1 x 10(-8) mol/L) and tartrazine (6 x 10(-6) mol/L), respectively, and the LOD for the C(4)D was for magnesium chloride (5 x 10(-7) mol/L). The advantage of the three different detection signals in a single point is demonstrated in capillary electrophoresis using model mixtures and s les including a mixture of fluorescent and nonfluorescent dyes and common ions, underivatized amino acids, and a fluorescently labeled digest of bovine serum albumin.
Microfluidic isotachophoresis: A review
Publisher: Wiley
Date: 14-05-2013
Abstract: Electromigration methods including CE and ITP are attractive for incorporation in microfluidic devices because they are relatively easily adaptable to miniaturization. After its popularity in the 1970s, ITP has made a comeback in microfluidic format (μ-ITP, micro-ITP) driven by the advantages of the steady-state boundary, the self-focusing effect, and the ability to aid in preconcentrating analytes in the s le while removing matrix components. In this review, we provide an overview of the developments in the area of μ-ITP in a context of the historic developments with a focus on recent developments in experimental and computational ITP and discuss possible future trends. The chip-ITP areas and topics discussed in this review and the corresponding sections include: PC simulations and modeling, analytical μ-ITP, preconcentration ITP, transient ITP, peak mode ITP, gradient elution ITP, and free-flow ITP, while the conclusions provide a critical summary and outlook. The review also contains experimental conditions for μ-ITP applications to real-world s les from over 50 original journal publications.
Polymerisation and surface modification of methacrylate monoliths in polyimide channels and polyimide coated capillaries using 660 nm light emitting diodes
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.CHROMA.2011.03.021
Abstract: An investigation into the preparation of monolithic separation media utilising a cyanine dye sensitiser/triphenylbutylborate/N-methoxy-4-phenylpyridinium tetrafluoroborate initiating system activated by 660 nm light emitting diodes is reported. The work demonstrates multiple uses of red-light initiated polymerisation in the preparation of monolithic stationary phases within polyimide and polyimide coated channels and the modification of monolithic materials with molecules which absorb strongly in the UV region. This initiator complex was used to synthesise poly(butyl methacrylate-co-ethylene dimethacrylate) and poly(methyl methacrylate-co-ethylene dimethacrylate) monolithic stationary phases in polyimide coated fused silica capillaries of varying internal diameters, as well as within polyimide micro-fluidic chips. The repeatability of the preparation procedure and resultant monolithic structure was demonstrated with a batch of poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths in 100 μm i.d. polyimide coated fused silica capillary, which were applied to the separation of a model protein mixture (ribonuclease A, cytochrome C, myoglobin and ovalbumin). Taking an average from 12 chromatograms originating from each batch, the maximum relative standard deviation of the retention factor (k) for the protein separations was recorded as 0.53%, the maximum variance for the selectivity factor (α) was 0.40% while the maximum relative standard deviation in peak resolution was 8.72%. All maxima were recorded for the Ribonuclease A/Cytochrome C peaks. Scanning electron microscopy confirmed the success of experiments in which poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths were prepared using the same initiation approach in capillary and micro-fluidic chips, respectively. The initiating system was also applied to the photo-initiated grafting of a chromophoric monomer onto poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths within poly(tetrafluoroethylene) coated fused silica capillaries.
UV-LED photopolymerised monoliths
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B802693A
Abstract: For the first time photopolymerisation of polymer monoliths has been realised with UV-light emitting diodes (LEDs) as light source and demonstrated with polymethacrylate monoliths created in fused silica capillaries and plastic chips.
Evanescent wave-initiated photopolymerisation as a new way to create monolithic open-tubular capillary columns: use as enzymatic microreactor for on-line protein digestion
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B920789A
Abstract: Evanescent wave-initiated photopolymerisation in an optically wave guiding PTFE-coated fused silica capillary using light-emitting diode as a light source, is established here as a way to fabricate monolithic porous layer open-tubular capillary columns with a potential in capillary separation methods application of the obtained open-tubular columns as enzymatic microreactors for on-line protein digestion is demonstrated.
Development of a fully buffered molybdate electrolyte for capillary electrophoresis with indirect detection and its use for analysis of anions in Bayer liquor
Publisher: Wiley
Date: 02-2004
Abstract: A new counterion-buffered molybdate electrolyte was developed and optimized for simultaneous quantitative determination of up to eight anions (chloride, sulphate, oxalate, fluoride, formate, malonate, succinate, and acetate) in Bayer liquor by capillary electrophoresis with indirect detection at 214 nm. The separation parameters were optimized in respect to separation of the critical analyte group fluoride-formate-malonate, with the optimal electrolyte prepared from molybdic trioxide containing 5.0 mmol/L MoO3, 1.3 mmol/L cetyltrimethylammonium bromide (CTAB), and buffered with diethanolamine (DEA) to pH 9.2 (ca. 20 mM DEA). Total length of separation capillary was 80 cm, resulting in run time of under 4 min. The method is suitable for a wide concentration range of the analytes (1-50 mg/L) with linear calibration plots (R2 = 0.9983-0.9999). Relative standard deviations were 0.05%-0.07% for migration times and 0.67%-2.04% for peak areas. The detection limits were in the range of 0.17-0.51 mg/L or 2-10 micromol/L (hydrostatic injection of 30 s of 1000 x diluted s le). Due to its good buffering capacity, the electrolyte exhibited an excellent ruggedness and good tolerance to the alkaline s les. Consequently, Bayer liquor s les could be diluted as little as 100 x which allows more sensitive determination of minor components over previous methods. The method was successfully applied to analysis of Bayer liquor s les with recoveries in the range of 95-105%.
Separation of some metallochromic ligands by capillary zone electrophoresis and micellar electrokinetic capillary chromatography
Publisher: Elsevier BV
Date: 07-1995
Mixed-mode capillary electrochromatographic separation of anionic analytes
Publisher: Royal Society of Chemistry (RSC)
Date: 1999
DOI: 10.1039/A904506F
Determination of calcium and magnesium in water samples by high- performance liquid chromatography on a graphitic stationary phase with a mobile phase containing o-cresolphthalein complexone
Publisher: Elsevier BV
Date: 11-1997
Enhancement of Separation Capability of Inorganic Ions by Capillary Electrochromatography
Publisher: Japan Society for Analytical Chemistry
Date: 2005
The use of the Box–Behnken experimental design in the optimisation and robustness testing of a capillary electrophoresis method for the analysis of ethambutol hydrochloride in a pharmaceutical formula
Publisher: Elsevier BV
Date: 03-2002
DOI: 10.1016/S0731-7085(01)00659-8
Abstract: Box-Behnken experimental designs do not appear to be extensively used in optimisation of analytical methods using capillary electrophoresis (CE). This paper describes the use of the Box-Behnken experimental design to optimise the factors affecting the separation of ethambutol hydrochloride (EB), its impurity 2-amino-1-butanol and the internal standard (phenylephrine hydrochloride) in a CE method for a pharmaceutical tablet assay. The three factors studied simultaneously were: buffer pH, buffer concentration and applied electric field, each at three levels. The method was optimised with respect to three responses: resolution between peaks, theoretical plate count and the migration time of the EB peak. A statistical programme, which applies a multiple response optimisation algorithm, was used to calculate and optimise the three responses simultaneously. The optimum conditions were established to be 58.0 mM sodium borate buffer at pH 9.50 and an applied electric field of 412 V/cm. The robustness of the method was also determined and confirmed using a second Box-Behnken design, as part of the validation exercise. System suitability values for the method were derived from the regression surface analysis. The CE method for a pharmaceutical tablet formulation was further validated according to current regulatory requirements, with respect to linearity and range, precision, specificity, accuracy and limit of quantitation. The optimised method gives a fast and efficient separation under 4 min, with complete resolution between the three peaks, and represents an improvement over the existing USP method. It can be concluded that the Box-Behnken experimental design provides a suitable means of optimising and testing the robustness of a CE pharmaceutical method.
Polystyrene bead-based system for optical sensing using spiropyran photoswitches
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B810080B
Robust monolithic silica-based on-chip electro-osmotic micro-pump
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B618386G
Abstract: A robust, compact, on-chip, electro-osmotic micro-pump (EOP) for micro-flow analysis, based on parallel, encased, 10 x 0.1 mm I.D. monolithic silica capillary columns has been developed. A 15 x 40 x 2 mm poly(methyl methacrylate) (PMMA) chip, containing a total of nine parallel EOP systems was fabricated, allowing the use of single, double or triple monolithic columns to produce increased flow as required. The monolithic silica was compatible with both aqueous and organic solvents without swelling or shrinking problems, with the triple column EOP capable of generating flow of up to 0.6 microL min(-1) under zero pressure load and over 0.1 microL min(-1) with an applied pressure of ca. 2.4 bar using an applied voltage of just 2 kV. Current generated at the 2 kV applied voltage for a 2 mM acetate buffer solution (pH 4.5) was under 4 microA, allowing stable, bubble-free flow. The developed triple column EOP was incorporated within a micro-fluidic chip (5.0 x 2.0 x 0.4 cm) integrated with a second single 10 x 0.1 mm column EOP, for combined s le injection and simple on-chip micro-flow analysis.
Preparation and characterisation of anion-exchange latex-coated silica monoliths for capillary electrochromatography
Publisher: Elsevier BV
Date: 03-2006
DOI: 10.1016/J.CHROMA.2005.08.076
Abstract: Silica monoliths coated with functionalised latex particles have been prepared for use in monolithic ion-exchange capillary electrochromatography (IE-CEC) for the separation of inorganic anions. The ion-exchange monoliths were prepared using 70 nm quaternary ammonium, anion-exchange latex particles, which were bound electrostatically to a monolithic silica skeleton synthesised in a fused silica capillary. The resulting stationary phases were characterised in terms of their chromatographic performance and capacity. The capacity of a 50 microm diameter 25 cm latex-coated silica monolith was found to be 0.342 nanoequivalents and 80,000 theoretical plates per column were typically achieved for weakly retained anions, with lower efficiency being observed for analytes exhibiting strong ion-exchange interaction with the stationary phase. The electroosmotic flow (EOF) was reversed after the latex-coating was applied (-25.96 m2 V(-1) s(-1), relative standard deviation (RSD) 2.8%) and resulted in anions being separated in the co-EOF mode. Ion-exchange interactions between the analytes and the stationary phase were manipulated by varying the ion-exchange selectivity coefficient and the concentration of a competing ion (phosphate or perchlorate) present in the electrolyte. Large concentrations of competing ion (greater than 1M phosphate or 200 mM perchlorate) were required to completely suppress ion-exchange interactions, which highlighted the significant retention effects that could be achieved using monolithic columns compared to open tubular columns, without the problems associated with particle-packed columns. The latex-coated silica monoliths were easily produced in bulk quantities and performed reproducibly in acidic electrolytes. The high permeability and beneficial phase ratio makes these columns ideal for micro-LC and preconcentration applications.
Analytical isotachophoresis of lactate in human serum using dry film photoresist microfluidic chips compatible with a commercially available field-deployable instrument platform
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.ACA.2013.01.046
Abstract: A dry film resist (DFR) chip compatible with the Agilent Bioanalyzer 2100 was designed and fabricated for use in the analysis of lactate in serum by chip isotachophoresis (ITP). The Agilent Bioanalyzer 2100 is a commercially available field deployable analytical instrument originally developed for the electrophoretic analysis of DNA, RNA and proteins. The DFR chip was designed for the ITP separation of lactate in human serum within 1 min and was made compatible with the Bioanalyzer after packaging in the plastic caddies normally used for the DNA chips. A 20-fold improvement in sensitivity was obtained for the DFR chips in comparison with the standard chips used in earlier work. The limit of detection and limit of quantification for lactate were 24 μM and 80 μM, respectively. This new approach enables the use of commercial platforms like the Agilent Bioanalyzer for new applications including the analysis of small molecules.
Spiropyran modified micro-fluidic chip channels as photonically controlled self-indicating system for metal ion accumulation and release
Publisher: Elsevier BV
Date: 06-2009
System peaks in capillary zone electrophoresis. 3. Practical rules for predicting the existence of system peaks in capillary zone electrophoresis of anions using indirect spectrophotometric detection
Publisher: Wiley
Date: 1997
Abstract: A theoretical and experimental study of the existence and evolution of system peaks in capillary zone electrophoresis (CZE) with indirect spectrophotometric detection is presented with respect to the effect of the number of coions present in the background electrolyte (BGE). It is shown that in BGEs having only one coion (i.e., the UV-absorbing probe anion), the s le produces only negative peaks due to each analyte anion and no system peaks, with the number of s le peaks corresponding to the number of analytes present in the s le injected. In BGEs containing two coions, a s le with one analyte anion produces one negative indirect detection peak and one system peak. The transition between BGEs having one coion and those with two coions has also been studied and it has been shown that an addition of ca. 5% of the second coion to a single coion BGE causes the resulting BGE to behave macroscopically as a regular two-coion BGE. A descriptive model is proposed, based on transient isotachophoresis (transient stacking) of the s le species and of the coion from the BGE which has the closest mobility to the s le ion. This model explains qualitatively the formation and evolution of the s le peak (containing the s le species and being detected by indirect detection due to displacement of the UV-absorbing probe in its zone) and the system peak (containing no s le species and being a vacancy in the continuum of coions of the BGE). It is shown that the system peak may be positive or negative as it corresponds to the situation where the vacancy of one component of the BGE results in an enhanced concentration of the other component. It has been demonstrated that the system peak is created by a vacancy of that component of the BGE which has the greatest difference in mobility relative to that of the s le species. On indirect detection in BGEs containing two coions the s le displaces predominantly the BGE coion which has a mobility closest to that of the analyte anion. In systems with BGEs containing two coions, a s le having n analytes produces n s le peaks and one system peak, the sign and magnitude of which are dependent on the sum of the UV absorbances of the analytes involved. The effect of bicarbonate from atmospheric CO2 has also been studied and it has been shown that weakly alkaline BGEs with a single anionic UV-absorbing coion, such as those currently used for anionic analyses with indirect detection, may suffer from the presence of system peaks due to bicarbonate.
Changes in Electrolyte pH Due to Electrolysis during Capillary Zone Electrophoresis
Publisher: American Chemical Society (ACS)
Date: 21-01-1998
DOI: 10.1021/AC970428P
UV-absorbance detector for HPLC based on a light-emitting diode
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B715681B
Abstract: A flow-through optical absorption detector for HPLC was constructed using a novel deep-UV light-emitting diode as radiation source with a peak emission wavelength of 255 nm. For measuring the transmitted intensity (a property correlated to Transmittance) a special UV-sensitive photodiode was employed. Besides the power source, no optical or electronic components other than an inexpensive operational lifier and a few passive components were necessary. The performance of the detector was tested with three substances, namely nitrobenzene, benzoic acid and methyl benzoate, which were separated by gradient elution using an acetonitrile/water mixture and tetrabutylammonium hydrogensulfate as pH-buffer. Calibration curves for concentrations between 1.6 microg.mL(-1) and 400 microg.mL(-1) (nitrobenzene) and 8 microg.mL(-1) and 2.5 mg.mL(-1) (benzoic acid and methyl benzoate) were determined and coefficients of determination, r(2), of 0.9945, 0.9972 and 0.9996 were obtained for quadratic curve fits for the 3 compounds respectively. Relative standard deviations (n = 7) for peak areas were determined as 0.35% (nitrobenzene, 80 microg.mL(-1)), 0.27% (benzoic acid, 400 microg.mL(-1)) and 0.83% (methyl benzoate, 200 microg.mL(-1)). The lower limits of detection were found to be 750 ng.mL(-1), 5.8 microg.mL(-1) and 12 microg.mL(-1) for nitrobenzene, benzoic acid and methyl benzoate respectively.
A novel highly flexible, simple, rapid and low-cost fabrication tool for paper-based microfluidic devices (μPADs) using technical drawing pens and in-house formulated aqueous inks
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1016/J.ACA.2016.03.018
Abstract: Paper-based microfluidic devices (μPADs) are capable of achieving rapid quantitative measurements of a variety of analytes inexpensively. μPADs rely on patterning hydrophilic-hydrophobic regions on a sheet of paper in order to create capillary channels within impermeable fluidic brakes on the paper. Here, we present a novel, highly flexible and low-cost fabrication method using a desktop digital craft plotter/cutter and technical drawing pens with tip size of 0.5 mm. The pens were used with either commercial black permanent ink for drawing fluidic brakes, or with specialty in-house formulated aqueous inks. With the permanent marker ink it was possible to create barriers on paper rapidly and in a variety of designs in a highly flexible manner. For instance, a design featuring eight reservoirs can be produced within 10 s for each μPAD with a consistent line width of brakes (%RSD < 1.5). Further, we investigated the optimal viscosity range of in-house formulated inks controlled with additions of poly(ethylene glycol). The viscosity was measured by capillary electrophoresis and the optimal viscosity was in the range of ∼3-6 mPa s. A functional test of these μPADs was conducted by the screening of antioxidant activity. Colorimetric measurements of flavonoid, phenolic compounds and DPPH free radical scavenging activity were carried out on μPADs. The results can be detected by the naked eye and simply quantified by using a camera phone and image analysis software. The fabrication method using technical drawing pens provides flexibility in the use of in-house formulated inks, short fabrication time, simplicity and low cost.
Beads-based system for optical sensing using spiropyran photoswitches
Publisher: IEEE
Date: 08-2007
Modelling of migration behaviour of inorganic anions in ion-exchange capillary electrochromatography
Publisher: Wiley
Date: 02-2001
DOI: 10.1002/1522-2683(200102)22:3<503::AID-ELPS503>3.0.CO;2-S
Determination of association constants of inorganic ions with C12- and C14-alkyldimethylammoniopropane sulfonate zwitterionic surfactants using capillary electrochromatography
Publisher: Elsevier BV
Date: 09-2001
Elution mechanism in electrostatic ion chromatography with histidine as an isoelectric ampholytic mobile phase
Publisher: Elsevier BV
Date: 07-2000
DOI: 10.1016/S0021-9673(00)00167-9
Abstract: Electrostatic ion chromatography (EIC) using a zwitterionic stationary phase (formed by coating a C18 material with a hydrophobic zwitterionic surfactant) was studied with a mobile phase comprising an aqueous solution of histidine at the pH of its isoelectric point, together with non-suppressed conductometric detection. Anions and cations were found to be eluted as separate peaks, unlike the elution behaviour observed on the same system when pure water was used as mobile phase. An explanation was suggested in terms of protonation equilibria of the overall uncharged histidine to form small amounts of histidine cations and anions in the mobile phase which could act as counterions for analyte anions and cations. This suggestion was supported by measured pH changes occurring in the bands of eluted analyte anions (a decreased pH compared to the mobile phase) and cations (an increased pH compared to the mobile phase). The analytical potential of this type of EIC is discussed.
Portable capillary-based (non-chip) capillary electrophoresis
Publisher: Elsevier BV
Date: 09-2010
Fibre coupled micro-light emitting diode array light source with integrated band-pass filter for fluorescence detection in miniaturised analytical systems
Publisher: Elsevier BV
Date: 04-2015
DOI: 10.1016/J.ACA.2015.02.044
Abstract: In this work, a new type of miniaturized fibre-coupled solid-state light source is demonstrated as an excitation source for fluorescence detection in capillary electrophoresis. It is based on a parabolically shaped micro-light emitting diode (μ-LED) array with a custom band-pass optical interference filter (IF) deposited at the back of the LED substrate. The GaN μ-LED array consisted of 270 in idual μ-LED elements with a peak emission at 470 nm, each about 14 μm in diameter and operated as a single unit. Light was extracted through the transparent substrate material, and coupled to an optical fibre (OF, 400 μm in diameter, numerical aperture NA=0.37), to form an integrated μ-LED-IF-OF light source component. This packaged μ-LED-IF-OF light source emitted approximately 225 μW of optical power at a bias current of 20 mA. The bandpass IF filter was designed to reduce undesirable LED light emissions in the wavelength range above 490 nm. Devices with and without IF were compared in terms of the optical power output, spectral characteristics as well as LOD values. While the IF consisted of only 7.5 pairs (15 layers) of SiO2/HfO2 layers, it resulted in an improvement of the baseline noise as well as the detection limit measured using fluorescein as test analyte, both by approximately one order of magnitude, with a LOD of 1×10(-8) mol L(-1) obtained under optimised conditions. The μ-LED-IF-OF light source was then demonstrated for use in capillary electrophoresis with fluorimetric detection. The limits of detection obtained by this device were compared to those obtained with a commercial fibre coupled LED device.
Mixed-mode electrokinetic chromatography of aromatic bases with two pseudo-stationary phases and pH control
Publisher: Elsevier BV
Date: 05-2003
DOI: 10.1016/S0021-9673(03)00064-5
Abstract: The electrokinetic chromatographic (EKC) separation of a series of aromatic bases was achieved utilising an electrolyte system comprising an anionic soluble polymer (polyvinylsulfonic acid, PVS) and a neutral beta-cyclodextrin (beta-CD) as pseudo-stationary phases. The separation mechanism was based on a combination of electrophoresis, ion-exchange interactions with PVS, and hydrophobic interactions with beta-CD. The extent of each chromatographic interaction was independently variable, allowing for control of the separation selectivity of the system. The ion-exchange and the hydrophobic interactions could be varied by changing the PVS and the beta-CD concentrations, respectively. Additionally, mobilities of the bases could be controlled by varying pH, due to their large range of pKa values. The separation system was very robust with reproducibility of migration times being <2% RSD. The two-dimensional parameter space defined by the two variables, [beta-CD] and %PVS, was modelled using a physical model derived from first principles. This model gave very good correlation between predicted and observed mobilities (r2=0.999) for the 13 aromatic bases and parameters derived from the model agreed with the expected ion-exchange and hydrophobic character of each analyte. The complexity of the mathematical model was increased to include pH and this three-dimensional system was modelled successfully using an artificial neural network (ANN). Optimisation of both the two-dimensional and three-dimensional systems was achieved using the normalised resolution product and minimum resolution criteria. An ex le of using the ANN to predict conditions needed to obtain a separation with a desired migration order between two of the analytes is also shown.
Temperature profiles and heat dissipation in capillary electrophoresis
Publisher: American Chemical Society (ACS)
Date: 24-02-2006
DOI: 10.1021/AC052075X
Abstract: While temperature control is usually employed in capillary electrophoresis (CE) to aid heat dissipation and provide acceptable precision, internal electrolyte temperatures are almost never measured. In principle, this limits the accuracy, repeatability, and method robustness. This work presents a fundamental study that combines the development of new equations characterizing temperature profiles in CE with a new method of temperature determination. New equations were derived from first principles relating the mean, axial, and inner wall electrolyte temperatures (T(Mean), T(Axis), T(Wall)). T(Mean) was shown to occur at a distance 1/ radical3 times the internal radius of the capillary from the center of the capillary and to be a weighted average of (2/3)T(Axis) and (1/3)T(Wall). Conductance (G) and electroosmotic mobility (mu(EOF)) can be used to determine T(Mean) and T(Wall), respectively. Extrapolation of curves of mu(EOF) versus power per unit length (P/L) at different temperatures was used to calibrate the variation of mu(EOF) with temperature (T), free from Joule heating effects. mu(EOF) increased at 2.22%/ degrees C. The experimentally determined temperatures using mu(EOF) agreed to within 0.2 degrees C with those determined using G. The accuracy of G measurements was confirmed independently by measuring the electrical conductivity (kappa) of the bulk electrolyte over a range of temperatures and by calculating the variation of G with T from the Debye-Hückel-Onsager equation. T(Mean) was found to be up to 20 degrees C higher than the external temperature under typical conditions using active air-cooling and a 74.0-microm-internal diameter (di) fused-silica capillary. A combination of experimentally determined and calculated temperatures enables a complete temperature profile for a fused-silica capillary to be drawn and the thickness of the stationary air layer to be determined. As an ex le, at P/L = 1.00 Wm(-1), the determined radial temperature difference across the electrolyte was 0.14 degrees C the temperature difference across the fused-silica wall was 0.17 degrees C, across the poly(imide) coating was 0.13 degrees C, and across the stationary air layer was 2.33 degrees C.
High sensitivity deep-UV LED-based z-cell photometric detector for capillary liquid chromatography
Publisher: Elsevier BV
Date: 11-2018
DOI: 10.1016/J.ACA.2018.06.005
Abstract: A new high sensitivity deep-UV LED photometric detector with a z-type flow cell (45 nL or 180 nL) for miniaturised and portable capillary liquid chromatography (LC) was designed and fabricated to overcome sensitivity limitations due to short pathlength in on-capillary detectors. The new detector has a 10 mm geometric pathlength and uses high intensity light-emitting diodes (LED) as light sources in the deep-UV range (254 nm and 280 nm). No optical reference was necessary due to the low drift in the signal. Stray light was minimized by the use of an adjustable slit with a 0.5 mm pinhole. The direct relationship between absorbance and concentration was obtained using dichromate to evaluate the sensitivity and the linearity range of the detector. Performance of the miniaturised version was compared with that obtained from a commercial benchtop detector for capillary LC under the same conditions using the same optical z-cell. The miniaturised version exhibited a superior performance across all parameters, including 3 times higher effective pathlength, 4 times higher upper limit of detector linearity, and 2-5 times lower stray light levels. An application of the new detector was shown with the detection of l-dopa, l-tyrosine, norfenefrine, phenylephrine and tyramine, separated using capillary LC. The baseline noise level recorded was as low as 3.9 μAU. Further, the detector was applied in a miniaturised capillary LC for the indirect detection of common inorganic anions. In comparison to an on-capillary LED detector applied under similar chromatographic conditions, there was a 50 times higher signal to noise (S/N) ratio.
Instrument-free argentometric determination of chloride via trapezoidal distance-based microfluidic paper devices
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.ACA.2019.02.048
Abstract: Chloride (Cl
Chromatographic behaviour of some platinum(II) complexes on octadecylsilica dynamically modified with a mixture of a cationic and an anionic amphiphilic modifier
Publisher: Elsevier BV
Date: 07-1993
Sensitive determination of carbohydrates labelled with p-nitroaniline by capillary electrophoresis with photometric detection using a 406 nm light-emitting diode
Publisher: Wiley
Date: 10-2006
Abstract: p-Nitroaniline was explored as a derivatising reagent for UV absorbance detection of carbohydrates after separation by CE. This derivatising agent has three advantages: first, it has excellent water solubility second, it has high molar absorptivity and third, it is possible to obtain sensitive detection using a UV or blue light-emitting diode (LED) as the light source. The labelling reaction took less than 30 min to complete with high reaction yield. The separation process was modelled and optimised using an artificial neural network. Nine carbohydrates were separated by a CE system within 16 min using a 0.17 M boric acid buffer at pH 9.7. On-column LED detection at 406 nm allowed the detection of carbohydrates with good detection limits (<1.1 microM or 8.8 fmol) and reproducible quantification in the concentration range of 2.6-200 microM. This method was applied successfully to the determination of component carbohydrates in some food s les.
Comparison of cation-exchange capillary columns used for ion chromatographic separation of biogenic amines
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.CHROMA.2018.08.021
Abstract: The selectivity for 15 biogenic amines and amino acids shown by three capillary cation-exchange columns, IonPac CS19, CS12A and CS17 (250 × 0.4 mm ID, all from Thermo Fisher Scientific), exhibiting medium, medium low and ultra-low hydrophobicity, and either carboxylic or mixed carboxylic hosphonic acid functional groups, was investigated. A mixed mode retention mechanism was revealed with ion-exchange, hydrophobic and hydrogen bonding interactions contributing to retention of polar organic molecules on these phases. The relative impact of these interactions was evaluated via the effect of concentration and pH of the eluent (methanesulfonic acid) on the retention of fifteen structurally similar biogenic amines and amino acids. Strong hydrogen bonding interactions were observed between the solute amino acid carboxylic groups and cation-exchange groups from the ion-exchangers. This is the first time retention data correlated with logP data has revealed clustering of the solutes in two groups, according to the presence or absence of a carboxylic acid functional group. In addition, stronger retention behaviour was found for the IonPac CS12A cation-exchanger, containing both carboxylic and phosphonic functional groups. Further assessment of the orthogonality plots of retention factors for the three stationary phases revealed that the columns exhibited different complimentary selectivity that can be utilised to achieve specific separations.
Pulsed potentiometric detection in capillary electrophoresis using platinum electrodes
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/B004952M
Electrokinetic Chromatography Utilizing Two Pseudostationary Phases Providing Ion-Exchange and Hydrophobic Interactions
Publisher: American Chemical Society (ACS)
Date: 16-02-2002
DOI: 10.1021/AC0109016
Abstract: The electrokinetic chromatographic separation of a series of inorganic and organic anions was achieved by utilizing an electrolyte system comprising a cationic soluble polymer (poly(diallydimethylammonium chloride, PDDAC) and a neutral beta-cyclodextrin (beta-CD) as pseudostationary phases. The separation mechanism was a combination of electrophoresis, ion-exchange (IE) interactions with PDDAC, and hydrophobic interactions with beta-CD. The extent of each chromatographic interaction was independently variable, allowing for control of the separation selectivity of the system. IE interactions could be varied by changing either the PDDAC concentration or the concentration of a competing ion (e.g., chloride) in the BGE, while the hydrophobic interactions could be varied by changing the concentration of beta-CD. The separation system was very robust, with the reproducibility of the migration times being <0.7% RSD. A mathematical model that predicted the mobilities of analytes under varying experimental conditions was derived and was shown to give good correlation (r2 = 0.9804) between predicted and experimental migration times. Parameters derived from the model were in good agreement with the ion-exchange and hydrophobic characteristics of the analytes. The model was also applied successfully to the optimization of conditions for the separation of a mixture of analytes or for conditions under which particular analytes migrated in a desired order. That is, the opportunity to tune the separation selectivity has been demonstrated.
Linearity evaluation in absorbance detection: The use of light-emitting diodes for on-capillary detection in capillary electrophoresis
Publisher: Wiley
Date: 1996
Abstract: A model which takes into account both stray light and polychromatic light was used to predict and evaluate linearity in on-capillary detection in capillary electrophoresis (CE). According to the model the stray light is the major factor which determines linearity under typical CE operating conditions. By calculating theoretical absorbance versus concentration plots, the influence of different levels of stray light and polychromatic light on linearity is demonstrated. Experimentally, six light-emitting diodes (LEDs) in the range from 563 to 654 nm were examined as light sources for on-capillary detection in CE. Fitting theoretical curves to measured linearity plots enabled determination of the values of both effective path length and stray light for a particular detection system. The detector linearity for the four LEDs was compared to mercury and tungsten l s used with interference filters. For potassium permanganate as the test compound, the linear range for a 563 nm LED was two times greater than that for a mercury l operated at 546 nm. The relatively poor linearity of the mercury l detector is explained by its high level of stray light. The noise of the LED563-based detector was the same as for the mercury l , whereas the other LEDs of higher light intensity gave approximately half the noise of the mercury l . The lowest noise level of 3 x 10(-5) AU was obtained for the LED at 554 nm (determined at a detector time constant of 0.1 s).
Separation of some platinum(II) complexes by ionic strength gradient on a solvent-generated ion-exchange sorbent
Publisher: Elsevier BV
Date: 11-1991
DOI: 10.1016/0021-9673(91)85135-3
Abstract: The compatibility of ionic strength gradient with solvent-generated ion-exchange chromatography on an octadecylsilica sorbent was proven for a mobile phase containing octanesulphonate. Only a slight baseline shift was observed during the gradient of the phosphate buffer, even at 210 nm. An equilibration time of 3 min between the runs was sufficient to obtain retention times with a reproducibility better than 1%. The compounds separated were cisplatin, carboplatin and related neutral and cationic platinum(II) complexes, including transplatin and the aquation products of cisplatin.
Indirect spectrophotometric detection of inorganic anions in ion-exchange capillary electrochromatography
Publisher: Wiley
Date: 09-2000
DOI: 10.1002/1522-2683(20000901)21:15<3073::AID-ELPS3073>3.0.CO;2-H
Variation of zeta-potential with temperature in fused-silica capillaries used for capillary electrophoresis
Publisher: Wiley
Date: 02-2006
Abstract: The temperature variation of electroosmotic mobility corrected for the effects of Joule heating (muEOF0) was employed to investigate the variation of the zeta-potential (zeta) with temperature in fused-silica capillaries. Experimentally determined values for zeta increased at 0.39% per degrees C, a rate that is about four to five times smaller than reported previously. Experimentally determined values of zeta were directly proportional to the absolute temperature although values were also influenced slightly by changes to the dielectric constant. It was found that the effective charge density at the inner surface of the capillary was independent of temperature.
White LEDs as broad spectrum light sources for spectrophotometry: Demonstration in the visible spectrum range in a diode-array spectrophotometric detector
Publisher: Wiley
Date: 11-2010
Abstract: Although traditional l s, such as deuterium l s, are suitable for bench-top instrumentation, their compatibility with the requirements of modern miniaturized instrumentation is limited. This study investigates the option of utilizing solid-state light source technology, namely white LEDs, as a broad band spectrum source for spectrophotometry. Several white light LEDs of both RGB and white phosphorus have been characterized in terms of their emission spectra and energy output and a white phosphorus Luxeon LED was then chosen for demonstration as a light source for visible-spectrum spectrophotometry conducted in CE. The Luxeon LED was fixed onto the base of a dismounted deuterium (D(2) ) l so that the light-emitting spot was geometrically positioned exactly where the light-emitting spot of the original D(2) l is placed. In this manner, the detector of a commercial CE instrument equipped with a DAD was not modified in any way. As the detector hardware and electronics remained the same, the change of the deuterium l for the Luxeon white LED allowed a direct comparison of their performances. Several anionic dyes as model analytes with absorption maxima between 450 and 600 nm were separated by CE in an electrolyte of 0.01 mol/L sodium tetraborate. The absorbance baseline noise as the key parameter was 5 × lower for the white LED l , showing clearly superior performance to the deuterium l in the available, i.e. visible part of the spectrum.
Artificial neural networks for computer-aided modelling and optimisation in micellar electrokinetic chromatography
Publisher: Elsevier BV
Date: 07-1999
DOI: 10.1016/S0021-9673(99)00634-2
Abstract: The separation process in capillary micellar electrochromatography (MEKC) can be modelled using artificial neural networks (ANNs) and optimisation of MEKC methods can be facilitated by combining ANNs with experimental design. ANNs have shown attractive possibilities for non-linear modelling of response surfaces in MEKC and it was demonstrated that by combining ANN modelling with experimental design, the number of experiments necessary to search and find optimal separation conditions can be reduced significantly. A new general approach for computer-aided optimisation in MEKC has been proposed which, because of its general validity, can also be applied in other separation techniques.
Use of dyes as indirect detection probes for the high-sensitivity determination of anions by capillary electrophoresis
Publisher: Elsevier BV
Date: 04-1998
Theoretical migration model for micellar capillary electrophoresis and its application to the separation of anionic metal complexes of HEDTC and CDTA
Publisher: American Chemical Society (ACS)
Date: 27-03-1999
DOI: 10.1021/AC981044H
Abstract: A mathematical model relating the effective mobility of an analyte in micellar capillary electrophoresis (MCE) to the concentration of surfactant and organic modifier in the background electrolyte (BGE) was derived. Effective mobility is expressed in terms of the electrophoretic mobility of the analyte, the partition coefficient of the analyte into the micelle, and the influence of organic modifier on these two factors. The performance of the model was evaluated using Cd(II), Pb(II), Co(II), Ni(II), Bi(III), Cu(II), and Hg(II) complexes of bis(2-hydroxyethyl)dithiocarbamate, all of which carry a partial negative charge, and Cd(II), Pb(II), Co(II), Ni(II), Bi(III), Cu(II), Hg(II), Fe(III), Ag(I), Tl(I), and Mn(II) complexes of trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, all of which are anionic having charges in the range -1 to -3. These analytes were separated in borate BGEs containing 10-50 mM sodium dodecyl sulfate and 0-20% (v/v) methanol. Nonlinear regression was used to derive parameters for the model from experimental data and these parameters were used to predict effective mobilities of the analytes. Predicted values of effective mobilties agreed with experimental values to within 3.1%. Values of parameters from the model equation are used to explain changes in separation selectivity observed at different BGE compositions and the model equation is shown to be applicable to computer-assisted optimization of the BGE composition, in MCE using a limited number of experiments.
Open-tubular ion-exchange capillary electrochromatography of inorganic anions
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/B002173N
Fluorinated ethylenepropylene copolymer as a potential capillary material in CE
Publisher: Wiley
Date: 10-2007
Abstract: In this work, a new generation UV-transparent polymer, fluorinated ethylenepropylene copolymer (FEP) exhibiting a low degree of crystallinity, extruded in dimensions similar to the most commonly used CE capillaries of approximately 80 mum id and about 360 mum od was investigated for its use as a CE capillary. FEP is transparent down to the low-UV region, and as fluorinated polymers in general are good electrical insulators and exhibit reasonable heat conductivity, it has considerable potential as a material for electrodriven analysis in capillary or microchip formats. The FEP capillary has been characterised with regard to some important aspects for its use as a CE capillary, including its profile of EOF versus pH, as well as procedures for manipulating EOF by coating the inner capillary wall with various semipermanent and dynamic layers. The FEP capillaries were tested and compared with fused-silica capillary for the separation of inorganic and small organic ions using conditions involving direct and indirect detection in the low-UV region. Finally, advantages of the use of the FEP capillary for simultaneous detection of a mixture containing nine inorganic cations and anions using indirect photometric detection with a movable light-emitting diode (LED) detector and a novel electrolyte are demonstrated.
A methodology to assess the spatial configuration of urban systems in Iran from an interaction perspective
Publisher: Springer Science and Business Media LLC
Date: 07-09-2015
Deep-UV-LEDs in photometric detection: A 255 nm LED on-capillary detector in capillary electrophoresis
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B916081G
Abstract: A 255 nm deep-UV-light-emitting diode (deep-UV-LED) is investigated as a novel light source for photometric detection in view of fundamental properties of UV-LEDs, in particular emission spectra and energy conversion. Its performance in on-capillary photometric detection in capillary electrophoresis (CE) is determined and the potential of deep-UV-LEDs in optical detection is discussed.
Separation and determination of vanadium in fertiliser by capillary electrophoresis with a light-emitting diode detector
Publisher: Springer Science and Business Media LLC
Date: 11-2002
DOI: 10.1007/S00216-002-1564-8
Abstract: A method has been developed for determination of vanadium, as an anionic ternary complex of vanadium(V) with 4-(2-pyridylazo) resorcinol (PAR) and hydrogen peroxide, after separation by capillary electrophoresis (CE). The optimum conditions for the formation of the ternary complex were acetate buffer (3 mmol L(-1)) at pH 6 containing 0.15 mmol L(-1) PAR and 7.1 mmol L(-1) H(2)O(2). The CE separation was conducted using 15 mmol L(-1) acetate buffer at pH 6 as the background electrolyte the separation potential was -30 kV and the injection time 100 s. The vanadium complex was detected photometrically at 568 nm, by use of a light-emitting diode (LED) the detection limit was 19 ppb. The method was applied to the analysis of vanadium in fertilisers. Clean-up of the digested fertiliser s le, with Sep-Pak C(18) coated with tetrabutylammonium hydroxide, before analysis was used to remove matrix ions which otherwise caused electrophoretic de-stacking. Vanadium levels found in the fertiliser s les by use of the CE method were found to be comparable with results obtained by HPLC and ICP-MS.
Micro-flow injection analysis system: On-chip sample preconcentration, injection and delivery using coupled monolithic electroosmotic pumps
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B707773B
Abstract: A micro-fluidic chip, within which two monolithic electroosmotic pumps are utilised for s le preconcentration, injection and delivery is presented. The monolithic pumps were capable of producing stable and bubble free flow rates at applied voltages below 2 kV, with a current <10 microA. Electrokinetic (EK) s le injection, down to low nano-litre volumes, was quantitatively controlled through applied voltage and injection times, whilst the s le pump delivered a carrier solution to indirectly dispense the s le. A nano-flow sensor (NFS) was used to continuously monitor the flow rate stability of each pump, showing response times of <5-10 s for changes in applied voltage. A capacitively coupled contactless conductivity detector (C(4)D), as an off-chip on-capillary detector, was used to complete the micro-flow injection analysis (FIA) system. A monolithic electroosmotic pump (EOP), modified with an anionic surfactant, was used to demonstrate a novel approach to on-chip cation preconcentration and elution.
Recent significant developments in detection and method development for the determination of inorganic ions by CE
Publisher: Wiley
Date: 06-2009
Abstract: CE has been available as a tool for almost 20 years, but it is only in the past several years that it has been implemented widely. This has been the result of some significant advances in the technique. These fall in the areas of indirect photometric detection (through the use of dyes as probes and LEDs as light sources), the introduction and establishment of capacitively-coupled contactless conductivity detection (C4D) as a routine, sensitive and commercially available detection method, and in software capable of simulation of separations and the selection of optimal composition of the BGE. These developments are reviewed and their impact illustrated by reference to a case study involving the rapid separation and sensitive detection of 15 anions and 12 cations on a portable CE instrument. It is shown that C4D provides considerably superior detection sensitivity (by a factor of about 8 in comparison with optimised indirect photometry).
Separation of metal ions and metal-containing species by micellar electrokinetic capillary chromatography, including utilisation of metal ions in separations of other species
Publisher: Elsevier BV
Date: 09-1997
Factors influencing the choice of buffer in background electrolytes for indirect detection of fast anions by capillary electrophoresis
Publisher: Wiley
Date: 09-1998
Abstract: The suitability of relatively slow (low absolute value of mobility) coanionic buffers in background electrolytes (BGEs) for indirect photometric detection of anions by capillary electrophoresis was investigated. As a model system, 2-(cyclohexylamino)ethanesulfonic acid (CHES) was used to buffer the indirect detection electrolyte of sodium chromate. CHES (PKa 9.55) is a zwitterionic molecule carrying a net negative charge depending on the pH (effective charge -0.5 at pH = pKa). Within its useful pH buffering range CHES acted as a competing probe coanion. System peaks were induced which had deleterious effects on the detection sensitivity of slow to medium mobility anions. The mobility of the system peak was determined by the effective mobility of CHES, both of which increased with increasing pH. The peaks of analytes that migrated near or on the system peak were distorted and lost all quantitative properties. Analytes that migrated after the system peak either were not detected or reversed their responses. Analytes that migrated well before the system peak were unaffected. Consequently, the suitability of slow coanionic buffers is limited either to (i) fast anions or, (ii) a pH range much below the PKa, where the buffering capacity is not optimal.
Using coupled monolithic rods for ultra-high peak capacity LC and LC-MS under normal LC operating pressures
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B714807K
Abstract: Up to ten in idual reversed-phase monolithic LC columns were efficiently coupled to equal a total column length of 1 m. The column generated up to 90,000 theoretical plates under optimum conditions with a peak capacity under gradient conditions of 244 peaks h(-1) at a total column backpressure of just 140 bar, directly coupled to ESI-MS.
Development of Microfluidic Chips for Heterogeneous Receptor-Ligand Interaction Studies
Publisher: American Chemical Society (ACS)
Date: 14-05-2009
DOI: 10.1021/AC9006649
Abstract: A simple microfluidic-based technique to quantitate the binding affinity between the glycopeptide antibiotics teicoplanin from Actinoplanes teicomyceticus and vancomycin from Streptomyces orientalis and 5-carboxyfluorescein-D-Ala-D-Ala-D-Ala (5-FAM-(DA)(3)) is described. In this work, (3-aminopropyl)triethoxysilane is used to modify the surfaces of a series of microchannels, and each channel is subsequently exposed to a solution of antibiotic for a few minutes. The antibiotic is retained after washing through electrostatic interactions, and the series of channels are subsequently exposed to an increasing concentration of 5-FAM-(DA)(3) followed by washing to exclude any nonspecific binding. The extent of fluorescence is quantified using a microscope fitted with a CCD camera. The binding constants for the interaction of teicoplanin and vancomycin with the fluorescent peptide were determined to be 6.03 +/- 0.97 x 10(4) and 4.93 +/- 1.13 x 10(4) M(-1), respectively, in good agreement with previous data. The ease of quantifying the extent of interaction in this microchip technique may prove powerful for exploration of a myriad of receptor-ligand pairs.
Isotachophoretic Fluorescence in Situ Hybridization of Intact Bacterial Cells
Publisher: American Chemical Society (ACS)
Date: 06-06-2017
DOI: 10.1021/ACS.ANALCHEM.7B00598
Abstract: A counter-pressure-assisted capillary isotachophoresis method in combination with a sieving matrix and ionic spacer was used to perform in-line fluorescence in situ hybridization (FISH) of bacterial cells. A high concentration of sieving matrix (1.8% w/v HEC) was introduced at one end of the capillary, and the bacterial cells were suspended in the spacer electrolyte for injection. Using a 2 min injection with 18 psi counter-pressure, 50% of the cells injected into the capillary were hybridized with the fluorescently labeled oligonucleotide, and the excess unhybridized probe was separated from the hybridized cell-probe complexes in a two-stage ITP method. With an LOD (6.0 × 10
Deep-UV Detector for HPLC with Light-Emitting Diode
Publisher: Swiss Chemical Society
Date: 29-10-2008
Preparation and characterisation of dual‐layer latex‐coated columns for open‐tubular capillary electrochromatographic preconcentration of cations combined in‐line with their separation by capillary el
Publisher: Wiley
Date: 03-2006
Abstract: A dual‐layer ion‐exchange latex‐coated column was prepared and characterised for on‐capillary preconcentration of cations using an open‐tubular ion‐exchange CEC format. After preconcentration, the analyte cations were eluted with a transient isotachophoretic gradient and separated by CE. The latex double layer was established by first coating the negatively charged wall of the capillary with a layer of cationic quaternary ammonium anion‐exchange Dionex AS5A latex particles (60 nm diameter), and then coating a layer of anionic sulphonated cation‐exchange Dionex CS3 latex particles (300 nm diameter) onto the underlying AS5A layer. The adhesion of layers is based on electrostatic attractions. Several dual‐layer capillaries were characterised for their EOF and ion‐exchange capacity and this showed that coatings could be prepared reproducibly by a simple flushing procedure. The dual‐layer columns exhibited a moderate, pH‐independent EOF ( ca. 26×10 −9 m 2 V −1 s −1 ) and an ion‐exchange capacity of 57 µequiv./g (or 2.69 nequiv./column). Using an 8 cm length of coated capillary combined with a 72 cm length of untreated capillary, a method for on‐line preconcentration and separation of monovalent organic bases, alkali metal ions and alkaline earth metal ions by CE was developed. Recoveries for the preconcentration step were 48% for 4‐methylbenzylammonium, 43% for benzylammonium, 30–32% for alkali metal ions and 71–75% for alkaline earth cations. In all cases, recoveries were reproducible with RSDs being less than 6.2%. The influences of the ion‐exchange selectivity coefficient of the analyte and the s le‐loading rate on analyte recovery were also examined. The proposed method was utilised for the determination of alkaline earth cations and low µM detection limits were obtained.
Performance of a simple UV LED light source in the capillary electrophoresis of inorganic anions with indirect detection using a chromate background electrolyte
Publisher: Royal Society of Chemistry (RSC)
Date: 15-11-2002
DOI: 10.1039/B210485G
Abstract: Light emitting diodes (LEDs) are known to be excellent light sources for detectors in liquid chromatography and capillary electromigration separation techniques, but to date only LEDs emitting in the visible range have been used. In this work, a UV LED was investigated as a simple alternative light source to standard mercury or deuterium l s for use in indirect photometric detection of inorganic anions using capillary electrophoresis with a chromate background electrolyte (BGE). The UV LED used had an emission maximum at 379.5 nm, a wavelength at which chromate absorbs strongly and exhibits a 47% higher molar absorptivity than at 254 nm when using a standard mercury light source. The noise, sensitivity and linearity of the LED detector were evaluated and all exhibited superior performance to the mercury light source (up to 70% decrease in noise, up to 26.2% increase in sensitivity, and over 100% increase in linear range). Using the LED detector with a simple chromate-diethanolamine background electrolyte, limits of detection for the common inorganic anions, Cl-, NO3-, SO4(2-), F- and PO4(3-) ranged from 3 to 14 microg L(-1), using electrostatic injection at -5 kV for 5 s.
Anion-exchange capillary electrochromatography with indirect UV and direct contactless conductivity detection
Publisher: Wiley
Date: 05-2001
DOI: 10.1002/1522-2683(200105)22:7<1273::AID-ELPS1273>3.0.CO;2-U
Separation of carboxylic acids in human serum by isotachophoresis using a commercial field-deployable analytical platform combined with in-house glass microfluidic chips
Publisher: Elsevier BV
Date: 11-2012
DOI: 10.1016/J.ACA.2012.10.022
Abstract: Portable and field deployable analytical instruments are attractive in many fields including medical diagnostics, where point of care and on-site diagnostics systems capable of providing rapid quantitative results have the potential to vastly improve the productivity and the quality of medical care. Isotachophoresis (ITP) is a well known electrophoretic separation technique previously demonstrated as suitable for miniaturization in microfluidic chip format (chip-ITP). In this work, a purpose-designed ITP chip compatible with a commercial end-used targeted microfluidic system was used to study different injection protocols and to evaluate the effect of the length of the separation channel on the analytical performance. The in-house ITP chips were made from Corning glass and compared to the commercial DNA chip for the ITP separation of anions from the hydrodynamic injection of human serum. Using the in-house ITP chip the isotachophoretic step of lactate from human serum was approximately two times longer. The results of this research suggested that microfluidic ITP with indirect fluorescence detection is a viable technique for separation of organic acids in human serum s les, especially when a chip with suitable design is used.
Rapid separations of nile blue stained microorganisms as cationic charged species by chip-CE with LIF
Publisher: Wiley
Date: 05-2012
Abstract: Rapid detection of microorganisms by alternative methods is desirable. Electromigration separation methods have the capability to separate microorganisms according to their charge and size and laser-induced fluorescence (LIF) detection have single‐cell detection capability. In this work, a new combined separation and detection scheme was introduced using chip‐based capillary electrophoresis (chip‐ CE ) platform with LIF detection. Three microorganisms E scherichia coli , S taphylococcus aureus , and C andida albicans were selected as representatives of G ram‐positive bacteria, G ram‐negative bacteria, and fungi. While their cells carry an overall negative charge in neutral to alkaline p H , staining them with nile blue ( NB ) provided highly sensitive LIF detection with excitation and emission wavelengths at 635 nm and 685 nm, respectively, and at the same time, the overall charge was converted to positive. Electrolyte p H and concentration of polyethylene oxide (PEO) significantly affected the resolution of the microorganisms. Their optimal separation in the 14 mm separation channel was achieved in less than 30 s ( R s 5.3) in an electrolyte consisting of 3.94 m M T ris, 0.56 m M boric acid, 0.013 m M ethylenediaminetetraacetic acid disodium salt dihydrate (pH 10.5), and 0.025% PEO, with injection/separation voltages of +1000/+1000 V . The separation mechanism is likely employing contributions to the overall cationic charge from both the prevalently anionic membrane proteins and the cationic NB . Importantly, the resulting cationic NB ‐stained cells exhibited excellent separation selectivity and efficiency of ∼38000 theoretical plates for rapid separations within 30–40 s. The results indicate the potential of chip‐ CE for microbial analysis, which offers separations of a wide range of species with high efficiency, sensitivity, and throughput.
Developments in sample preparation and separation techniques for the determination of inorganic ions by ion chromatography and capillary electrophoresis
Publisher: Elsevier BV
Date: 09-1999
DOI: 10.1016/S0021-9673(99)00431-8
Abstract: A review is presented of s le preparation and separation techniques for the determination of inorganic ions by ion chromatography (IC) and capillary electrophoresis (CE). Emphasis has been placed on those s le treatment methods which are specific to inorganic analysis, and the developments in separation methods which are discussed are those which enhance the capabilities of IC and CE to handle complex s le matrices. Topics discussed include solid-phase extraction for s le clean-up and preconcentration, dialytic methods, combustion methods, matrix-elimination IC, electrostatic IC, electrically polarised ion-exchange resins, electromigration s le preparation in CE, chromatographic s le preparation for CE, use of high-ionic strength background electrolytes, buffering of background electrolytes in CE, use of capillary electrochromatography for inorganic determinations, and methods for the manipulation of separation selectivity in both IC and CE. Finally, some possible future trends are discussed.
Erratum: Temperature profiles and heat dissipation in capillary electrophoresis (Analytical Chemistry (2006) 78, (2684-2693))
Publisher: American Chemical Society (ACS)
Date: 07-03-2007
DOI: 10.1021/AC070216K
Identification of inorganic improvised explosive devices by analysis of postblast residues using portable capillary electrophoresis instrumentation and indirect photometric detection with a light-emitting diode
Publisher: American Chemical Society (ACS)
Date: 18-08-2007
DOI: 10.1021/AC0708792
Abstract: A commercial portable capillary electrophoresis (CE) instrument has been used to separate inorganic anions and cations found in postblast residues from improvised explosive devices (IEDs) of the type used frequently in terrorism attacks. The purpose of this analysis was to identify the type of explosive used. The CE instrument was modified for use with an in-house miniaturized light-emitting diode (LED) detector to enable sensitive indirect photometric detection to be employed for the detection of 15 anions (acetate, benzoate, carbonate, chlorate, chloride, chlorite, cyanate, fluoride, nitrate, nitrite, perchlorate, phosphate, sulfate, thiocyanate, thiosulfate) and 12 cations (ammonium, monomethylammonium, ethylammonium, potassium, sodium, barium, strontium, magnesium, manganese, calcium, zinc, lead) as the target analytes. These ions are known to be present in postblast residues from inorganic IEDs constructed from ammonium nitrate/fuel oil mixtures, black powder, and chlorate erchlorate/sugar mixtures. For the analysis of cations, a blue LED (470 nm) was used in conjunction with the highly absorbing cationic dye, chrysoidine (absorption maximum at 453 nm). A nonaqueous background electrolyte comprising 10 mM chrysoidine in methanol was found to give greatly improved baseline stability in comparison to aqueous electrolytes due to the increased solubility of chrysoidine and its decreased adsorption onto the capillary wall. Glacial acetic acid (0.7% v/v) was added to ensure chrysoidine was protonated and to enhance separation selectivity by means of complexation with transition metal ions. The 12 target cations were separated in less than 9.5 min with detection limits of 0.11-2.30 mg/L (calculated at a signal-to-noise ratio of 3). The anions separation system utilized a UV LED (370 nm) in conjunction with an aqueous chromate electrolyte (absorption maximum at 371 nm) consisting of 10 mM chromium(VI) oxide and 10 mM sodium chromate, buffered with 40 mM tris(hydroxymethyl)aminomethane at pH 8.05. All 15 target anions were baseline separated in less than 9 min with limits of detection ranging from 0.24 to 1.15 mg/L (calculated at a signal-to-noise ratio of 3). Use of the portable instrumentation in the field was demonstrated by analyzing postblast residues in a mobile laboratory immediately after detonation of the explosive devices. Profiling the ionic composition of the inorganic IEDs allowed identification of the chemicals used in their construction.
Peak shapes in open tubular ion-exchange capillary electrochromatography of inorganic anions
Publisher: Elsevier BV
Date: 09-2000
DOI: 10.1016/S0021-9673(00)00092-3
Abstract: An experimental study of parameters influencing peak shapes in ion-exchange open tubular (OT) capillary electrochromatography (CEC) was conducted using adsorbed quaternary aminated latex particles as the stationary phase. The combination of separation mechanisms from both capillary electrophoresis and ion-exchange chromatography results in peak broadening in OT-CEC arising from both these techniques. The sources of peak broadening that were considered included the relative electrophoretic mobilities of the eluent co-ion and analyte, and resistance to mass transfer in both the mobile and stationary phases. The parameters investigated were the mobility of the eluent co-ion, column diameter, separation temperature and secondary interactions between the analyte and the stationary phase. The electromigration dispersion was found to influence peak shapes to a minor extent, indicating that chromatographic retention was the dominant source of dispersion. Improving the resistance to mass transfer in the mobile phase by decreasing the capillary diameter improved peak shapes, with symmetrical peaks being obtained in a 25 microm I.D. column. However, an increase in temperature from 25 degrees C to 55 degrees C failed to show any significant improvement. The addition of p-cyanophenol to the mobile phase to suppress secondary interactions with the stationary phase did not result in the expected improvement in efficiency.
Determination of Acyclovir in Blood Serum and Plasma by Micellar Liquid Chromatography with Fluorimetric Detection
Publisher: Informa UK Limited
Date: 08-1993
Use of contactless conductivity detection for non-invasive characterisation of monolithic stationary-phase coatings for application in capillary ion chromatography
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B711350A
Abstract: A capacitively-coupled contactless conductivity detector (C4D) has been utilised as an on-capillary detector within a capillary ion chromatograph, incorporating a reversed-phase monolithic silica capillary column semi-permanently modified with a suitable ionic surfactant. The monolithic capillary column (150 x 0.1 mm i.d.) was modified using sodium dioctyl sulfosuccinate (DOSS), an anionic surfactant, for the separation of small inorganic and organic cations. With the use of the on-capillary conductivity detector, the longitudinal homogeneity and temporal stability of the coating were investigated. The approach allowed a detailed non-invasive observation of the nature of the ion-exchange coating over time, and an ex le of an application of the technique to produce a longitudinal stationary-phase charge gradient is shown. An investigation of the basis of the measured on-capillary conductivity was carried out with a counter ion study, clearly showing the on-capillary detection technique could also distinguish between chemical forms of the immobilised ion exchanger. The above method was used to produce a stable and homogeneously-modified monolithic ion-exchange capillary column, for application to the separation of inorganic alkaline earth cations and amino acids.
Separation of uranium(VI) and lanthanides by capillary electrophoresis using on-capillary complexation with arsenazo III
Publisher: Elsevier BV
Date: 04-1998
Selectivity control in the separation of aromatic amino acid enantiomers with sulphated β-cyclodextrin
Publisher: Elsevier BV
Date: 03-2004
DOI: 10.1016/J.CHROMA.2003.11.013
Abstract: Control of selectivity in the enantiomeric separation of three aromatic amino acids (phenylalanine, tyrosine and tryptophan) is demonstrated by electrokinetic capillary chromatography utilising temperature variations coupled with the use of sulphated-beta-cyclodextrin (s-beta-CD) as a pseudostationary phase. The concentration of s-beta-CD and temperature were used as experimental variables to control the observed selectivity. A double-coated capillary was used and proved very robust with reproducibility of migration times being <2.0% R.S.D. between runs and 100 microA). Using a 50 microm i.d. capillary and an electrolyte comprising 20 mM phosphate and 15 mM s-beta-CD, a temperature of 52 degrees C was calculated within the capillary at an applied voltage of +30 kV.
Solid-phase trapping of solutes for further chromatographic or electrophoretic analysis
Publisher: Elsevier BV
Date: 11-2000
DOI: 10.1016/S0021-9673(00)00792-5
Abstract: Because of its simplicity, speed and effectiveness, solid-phase extraction (SPE) has become the preferred technique for concentration of selected analytes prior to chromatographic or electrophoretic analysis. In this review the historical development of SPE is briefly traced. Then the principles of SPE are reviewed in some detail. Numerous references are given on the format, sorbents, elution conditions, online techniques and automation with special emphasis on relatively recent developments. The principles and recent advances in solid-phase microextraction (SPME) are also reviewed. The final section on selected recent applications includes an extensive list of references to work published within the last three years. Future trends and developments are discussed briefly.
Visible light initiated polymerization of styrenic monolithic stationary phases using 470 nm light emitting diode arrays
Publisher: Wiley
Date: 2010
The use of scanning contactless conductivity detection for the characterisation of stationary phases in micro-fluidic chips
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C003584J
Abstract: The use of scanning capacitively coupled contactless conductivity detection for the evaluation of the structural homogeneity and density of both packed and monolithic stationary phases in micro-fluidic chips is presented here for the first time.
Modification of the electroosmotic flow and separation selectivity of anions in electrochromatography with pseudo-stationary phases of C14-alkyldimethylammoniopropane sulfonate zwitterionic surfactant
Publisher: Springer Science and Business Media LLC
Date: 10-2001
Abstract: The effects of salts (NaCl, NaClO4, MgCl2, CeCl3) added to background electrolyte (BGE) solutions (10 mmol L(-1) sodium phosphate, pH 7.2) on electroosmotic flow (EOF) and the separation selectivity of anions (chloride, bromide, iodide, nitrite, nitrate, chlorate, thiocyanate, iodate, chromate, and molybdate ion) by capillary electrochromatography using the zwitterionic surfactant 3-(N,N-dimethylmyristylammonio)propane sulfonate (C14N3S) as a pseudo-stationary phase were investigated. There are two mechanisms affecting the separations: 1. the cations and anions of the added salts interact with the zwitterionic surfactant to varying degrees, thus changing the overall retention of the analytes and 2. they change the EOF and the resulting apparent mobilities. It was shown that a BGE containing perchlorate and a low concentration of zwitterionic surfactant (2 mmol L(-1)) gave a stable and reproducible EOF and the concentration of perchlorate could be used to manipulate the separation selectivity for polarizable anions, such as iodide and thiocyanate. These effects are discussed in terms of measured association constants describing the interaction of anions and cations with the zwitterion.
Determination of inorganic ions using microfluidic devices
Publisher: Wiley
Date: 11-2004
Abstract: The separation and detection of inorganic ions on microfluidic devices has received little attention since the ‘lab‐on‐a‐chip’ concept has revolutionised the field of electrokinetically driven analysis. This review presents a summary and discussion of the published literature on inorganic analysis using microfluidic devices and includes sections on electromigration separation methods, namely isotachophoresis (ITP), capillary electrophoresis (CE), and hyphenated ITP‐CE, together with a brief account of flow injection analysis. The review concludes with the authors' perspective on future directions for inorganic analysis on microfluidic devices.
Web-Based Cognitive Bias Modification Program for Young People With Social Anxiety and Hazardous Alcohol Use: Feasibility, Acceptability, and Preliminary Efficacy Study
Publisher: JMIR Publications Inc.
Date: 25-10-2023
DOI: 10.2196/46008
Reliable electrophoretic mobilities free from Joule heating effects using CE
Publisher: Wiley
Date: 10-2007
Abstract: Ionic electrophoretic mobilities determined by means of CE experiments are sometimes different when compared to generally accepted values based on limiting ionic conductance measurements. While the effect of ionic strength on electrophoretic mobility has been long understood, the increase in the mobility that results from Joule heating (the resistive heating that occurs when a current passes through an electrolyte) has been largely overlooked. In this work, a simple method for obtaining reliable and reproducible values of electrophoretic mobility is described. The electrophoretic mobility is measured over a range of driving powers and the extrapolation to zero power dissipation is employed to eliminate the effect of Joule heating. These extrapolated values of electrophoretic mobility can then be used to calculate limiting ionic mobilities by making a correction for ionic strength this somewhat complicated calculation is conveniently performed by using the freeware program PeakMaster 5. These straightforward procedures improve the agreement between experimentally determined and literature values of limiting ionic mobility by at least one order of magnitude. Using Tris-chromate BGE with a value of conductivity 0.34 S/m and ionic strength 59 mM at a modest dissipated power per unit length of 2.0 W/m, values of mobility for inorganic anions were increased by an average of 12.6% relative to their values free from the effects of Joule heating. These increases were accompanied by a reduction in mobilities due to the ionic strength effect, which was 11% for univalent and 28% for alent inorganic ions compared to their limiting ionic mobilities. Additionally, it was possible to determine the limiting ionic mobility for a number of aromatic anions by using PeakMaster 5 to perform an ionic strength correction. A major significance of this work is in being able to use CE to obtain reliable and accurate values of electrophoretic mobilities with all its benefits, including understanding and interpretation of physicochemical phenomena and the ability to model and simulate such phenomena accurately.
CE study of neuroprotective humanin peptide and its derivatives: Interactions with phosphate, sulphate, alkylsulphonates and sulphated-beta-CD
Publisher: Wiley
Date: 02-2008
Abstract: Humanin (HN), Met-Ala-Pro-Arg-Gly-Phe-Ser-Cys-Leu-Leu-Leu-Leu-Thr-Ser-Glu-IIe-Asp-Leu-Pro-Val-Lys-Arg-Arg-Ala, recently discovered in the human brain, is an important neuroprotective peptide. Some derivatives of HN show even higher biological activity, for ex le [G-14]-HN, where Ser at position 14 is replaced with Gly. As structurally related HN peptide derivatives have similar chemical properties, their separation by CE is difficult. In this work, the electrophoretic behaviour of HN derivatives including [G-14]-HN, a tryptophan HN derivative [W-14]-HN, several other HN derivatives and HN fragments was studied. While phosphate buffer was used as the general BGE, the effects of the buffer concentration and various additives were examined, including sulphate, heptane sulphonate, 2-morpholinoethanesulphonic acid N-[tris(hydroxymethyl)methyl]-2-aminoethane sulphonic acid (TES), sulphated-beta-CD and beta-CD. Separation efficiency of 200,000 theoretical plates was achieved in a BGE of 80 mM phosphate at pH 2.5 where seven out of nine major peaks were partially separated. By investigating the influence of concentration of the interrogated ions on peptides migration, the association between positively charged protonated sites of peptides and various anions was proved. Especially a strong interaction with phosphate, sulphate and sulphonate groups was established. Conditional stability constant of the [Pep(z+), (H(2)PO(4)(-))(n)](z - n) ion associate (n = 1) for [G-14]-HN equals to log K approximately 1.78.
Separation of Metal Bis(2-hydroxyethyl)dithiocarbamate Complexes by Micellar Electrokinetic Capillary Chromatography
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A607770F
Inorganic monoliths in separation science: A review
Publisher: Elsevier BV
Date: 10-2012
DOI: 10.1016/J.ACA.2012.04.029
Abstract: The practical application of rigid, macro-porous organic polymer and silica based monolithic stationary phases as separation media has been described in the literature since 1992 and 1996, respectively. Today these materials are extensively used in chromatography and electrochromatography and several detailed reviews appear annually describing these materials, their synthesis and application. To compliment these publications, this review focuses upon the less commonly utilised materials for monolith synthesis, both those that have already been applied within separation science, and those that have found applications elsewhere, such as catalysis and water filtration, but have the clear potential to be explored as novel stationary phases in the near future. For the purpose of the review monoliths formed from these various alternative materials will be termed 'Exotic Monoliths', as these new substrates in many cases have only just begun to be explored for chromatographic separations, and in many instances have unusual and highly selective surface chemistries, which are attractive in terms of broadening the choice of monolithic materials for separation science. An extensive range of monolithic materials based on the following elements and their compounds (mostly oxides) are covered: Zr, Ti, Al, Hf, C, Au, Ag, Ce, Ge and hydroxyapatite, together with their relevant properties, methods of synthesis, and current and potential applications in separation science.
Radiometric characterisation of light sources used in analytical chemistry – A review
Publisher: Elsevier BV
Date: 08-2020
Evaluation of monolithic and sub 2 μm particle packed columns for the rapid screening for illicit drugs - Application to the determination of drug contamination on Irish euro banknotes
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B615669J
Abstract: A study comparing recently available 100 x 3 mm id, 200 x 3 mm id monolithic reversed-phase columns with a 50 x 2.1 mm id, 1.8 microm particle packed reversed-phase columns was carried out to determine the most efficient approach (using traditional van Deemter analysis and a modern kinetic plot approach) for the rapid screening of s les for 16 illicit drugs and associated metabolites. A plot of column backpressure versus plate number (N) showed a significant advantage of using the monolithic phases, with the 20 cm monolithic column exhibiting a maximum 15,000 plates at a column backpressure of approximately 70 bar, compared to approximately 7000 plates at 150 bar for the 5 cm 1.8 microm particle packed column. Optimum linear velocities were found to be 0.40 mm s(-1), 0.52 mm s(-1) and 0.98 mm s(-1) for the three above columns, respectively. The 20 cm monolithic column was subsequently applied to the separation and determination of illicit drug contamination on Irish euro banknotes, using methanol extraction followed by LC-MS/MS. Method performance data showed that the new LC-MS/MS method was significantly more sensitive than previous GC-MS/MS based methods for this application, with detection limits in the pg note(-1) region, based upon a 20 microL standard injection. All of the notes examined tested positive for trace quantities of cocaine, with benzoylecgonine detected on 12 of the 45 notes s led. Traces of heroin were also detected on three of the 45 notes.
Miniature Multiwavelength Deep UV-LED-Based Absorption Detection System for Capillary LC
Publisher: American Chemical Society (ACS)
Date: 28-09-2020
Determination of the surface heat-transfer coefficient in CE
Publisher: Wiley
Date: 03-2200
Abstract: A knowledge of the heat-transfer coefficient, h(s), for the external surface of the capillary or the overall heat coefficient, h(OA), is of great value in predicting the mean increase in temperature of the electrolyte, DeltaT(Mean), during electrokinetic separations. For CE, traditional indirect methods of determining h(s) were time-consuming and tended to overestimate cooling efficiency a novel method is introduced, which is based on curve-fitting of plots of conductance versus voltage to calculate several important parameters including DeltaT(Mean), h(s), the conductance free of Joule heating effects (G(0)) and the voltage that causes autothermal runaway, V(lim). The new method is superior to previously published methods in that it can be performed more quickly and that it corrects for systematic errors in the measurement of electric current for voltages <5 kV. These errors tended to exaggerate the cooling efficiency of commercial instruments so that the calculated increases in electrolyte temperature were smaller than their actual values. Axially averaged values for h(s) were determined for three different commercial CE instruments ranging from 164 W m(-2) K(-1) for a passively cooled instrument in a drafty environment to 460 W m(-2) K(-1) for a liquid-cooled instrument.
Prospects of pulsed amperometric detection in flow-based analytical systems - A review
Publisher: Elsevier BV
Date: 04-2019
DOI: 10.1016/J.ACA.2018.10.066
Abstract: Electrochemical (EC) detection techniques in flow-based analytical systems such as flow injection analysis (FIA), capillary electrophoresis (CE), and liquid chromatography (LC) have attracted continuous interest over the last three decades, leading to significant advances in EC detection of a wide range of analytes in the liquid phase. In this context, the unique advantages of pulsed erometric detection (PAD) in terms of high sensitivity and selectivity, and electrode cleaning through the application of pulsed potential for noble metal electrodes (e.g. Au, Pt), have established PAD as an important detection technique for a variety of electrochemically active compounds. PAD is especially valuable for analytes not detectable by ultraviolet (UV) photometric detection, such as organic aliphatic compounds and carbohydrates, especially when used with miniaturised capillary and chip-based separation methods. These applications have been accomplished through advances in PAD potential waveform design, as well as through the incorporation of nanomaterials (NMs) employed as microelectrodes in PAD. PAD allows on-line pulsed potential cleaning and coupling with capillary or standard separation techniques. The NMs are largely employed in microelectrodes to speed up mass and electron transfer between electrode surfaces and to perform as reactants in EC analysis. These advances in PAD have improved the sensitive and selective EC detection of analytes, especially in biological s les with complex s le matrices, and detection of electro-inactive compounds such as aliphatic organic compounds (i.e., formic acid, acetic acid, maleic acids, and β-cyclodextrin complexes). This review addresses the fundamentals of PAD, the role of pulsed sequences in AD, the utilisation of different EC detectors for PAD, technological advancements in PAD waveforms, utilisation of microelectrodes in PAD techniques, advances in the use of NMs in PAD, the applications of PAD, and prospects for EC detection, with emphasis on PAD in flow-based systems.
Optimisation of selectivity in the separation of aromatic amino acid enantiomers using sulfatedß-cyclodextrin and dextran sulfate as pseudostationary phases
Publisher: Wiley
Date: 2004
Abstract: Control of selectivity in the enantiomeric separation of three aromatic amino acids (phenylalanine, tyrosine and tryptophan) was demonstrated utilising two separate electrolyte additives. Sulfated-beta-cyclodextrin (s-beta-CD) was chosen as the chiral selector while the addition of dextran sulfate provided a means with which to predictably fine-tune separation selectivity. The two additives were found to interact independently with the amino acids, with the s-CD providing chiral interactions while the dextran sulfate provided ion-exchange (IE) interactions. The system was also very robust with reproducibility of migration times being < 2.0% RSD between runs and < 2.6% on using a new capillary. A physical model derived from first principles was also successfully used to describe the two additive system. The model accurately described the observed separations over the range of 0-20 mM s-beta-CD and 0-1% dextran sulfate with a correlation coefficient of 0.998 between predicted and observed mobilities. The physical model also provided useful information about the system including association constants between the analytes and the pseudostationary phases, together with the mobilities of the associated complexes (analyte-cyclodextrin and analyte-dextran sulfate). Selectivity optimisation was achieved using the normalised resolution product and minimum resolution criteria. The physical model also allowed a desired separation selectivity to be obtained, such that experimental conditions could be predicted to lead to a particular migration order.
On-column ion-exchange preconcentration of inorganic anions in open tubular capillary electrochromatography with elution using transient-isotachophoretic gradients. 3. Implementation and method development
Publisher: American Chemical Society (ACS)
Date: 22-03-2002
DOI: 10.1021/AC011217U
Abstract: A solid-phase extraction method based on an ion-exchange retention mechanism has been used for in-line preconcentration of inorganic anions prior to their separation by capillary electrophoresis (CE). A single capillary containing a preconcentration and a separation zone has been used in a commercial CE instrument without instrumental modification. Analyte anions were retained on a preconcentration zone comprising an adsorbed layer of cationic latex particles, while separation was achieved in a separation zone comprising fused silica modified by adsorption of a cationic polymer. Elution of the adsorbed analytes was achieved using an eluotropic gradient formed by a transient isotachophoretic boundary between a fluoride electrolyte and a naphthalenedisulfonate electrolyte. Optimization of the electrolyte concentrations, s le injection times, and back-flushing times allowed the successful separation of sub-ppb levels of inorganic anions using a 100-min injection at 2 bar pressure, introducing over 40 capillary volumes of s le. A method based on a 10-min injection allowed a 100-fold increase in sensitivity over conventional hydrodynamic injection for Br-, I-, NO3-, CrO4(2-), and MoO4(2-) with a total analysis time of 25 min. Detection limits were dependent on the injection time but were in the range 2.2-11.6 ppb for a 10-min injection time. This approach was used to determine NO3- in Antarctic ice cores where the analysis could be performed using a s le volume 100 times less than that used for ion chromatography.
New Fully Portable Instrument for the Versatile Determination of Cations and Anions by Capillary Electrophoresis with Contactless Conductivity Detection
Publisher: Wiley
Date: 10-2007
Abstract: A new portable capillary electrophoresis instrument with capacitively coupled contactless conductivity detection was developed and optimized for the sensitive field measurements of ionic compounds in environmental s les. It is powered by batteries and the high voltage modules are capable of delivering up to 15 kV at either polarity for more than one working day. Inorganic cations and anions, including ions of heavy metals and arsenate, could be determined with detection limits in the range from about 0.2 to 1 μM. The instrument was field tested in a remote region of Tasmania and nitrite and ammonium could be determined on‐site at concentrations as low as 10 ppb in presence of other common inorganic ions at concentrations which were 2 to 3 orders of magnitude higher.
Analysis of silanised polyglycerols by supercritical fluid chromatography
Publisher: Elsevier BV
Date: 07-1994
Separation of superparamagnetic magnetite nanoparticles by capillary zone electrophoresis using non-complexing and complexing electrolyte anions and tetramethylammonium as dispersing additive
Publisher: Wiley
Date: 25-04-2018
Abstract: Separations of bare superparamagnetic magnetite nanoparticles (BSPMNPs, approx. 11 nm diameter) was performed using non-complexing (nitrate) and complexing (chloride, citrate and phosphate) electrolyte ions with additions of tetramethylammonium hydroxide (TMAOH), which is commonly applied to control the synthesis of stable iron oxides. The use of TMAOH as a background electrolyte (BGE) additive for capillary electrophoresis (CE) separations provided for the first time electropherograms of BSPMNPs exhibiting symmetrical and highly reproducible peaks, free of spurious spikes characteristic of nanoparticle clusters. Consequently, accurate determination of the electrophoretic effective mobility of BSPMNPs was possible, yielding a value of -3.345E-08 m
Determination of barium and strontium by capillary zone electrophoresis using an electrolyte containing sulfonazo III
Publisher: Elsevier BV
Date: 04-1997
Conductivity detection for conventional and miniaturised capillary electrophoresis systems
Publisher: Wiley
Date: 12-2004
Abstract: Since the introduction of capillary electrophoresis (CE), conductivity detection has been an attractive means of detection. No additional chemical properties are required for detection, and no loss in sensitivity is expected when miniaturising the detector to scale with narrow‐bore capillaries or even to the microchip format. Integration of conductivity and CE, however, involves a challenging combination of engineering issues. In conductivity detection the resistance of the solution is most frequently measured in an alternating current (AC) circuit. The influence of capacitors both in series and in parallel with the solution resistance should be minimised during conductivity measurements. For contact conductivity measurements, the positioning and alignment of the detection electrodes is crucial. A contact conductivity detector for CE has been commercially available, but was withdrawn from the market. Microfabrication technology enables integration and precise alignment of electrodes, resulting in the popularity of conductivity detection in microfluidic devices. In contactless conductivity detection, the alignment of the electrodes with respect to the capillary is less crucial. Contactless conductivity detection (CCD) was introduced in capillary CE, and similar electronics have been applied for CCD using planar electrodes in microfluidic devices. A contactless conductivity detector for capillaries has been commercialised recently. In this review, different approaches towards conductivity detection in capillaries and chip‐based CE are discussed. In contrast to previous reviews, the focus of the present review is on the technological developments and challenges in conductivity detection in CE.
Biopolymer-coated fused silica capillaries for high magnitude cathodic or anodic electro-osmotic flows in capillary electrophoresis
Publisher: Springer Science and Business Media LLC
Date: 2003
DOI: 10.1007/BF02492101
High-throughput deposition of chemical reagents via pen-plotting technique for microfluidic paper-based analytical devices
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.ACA.2018.09.006
Abstract: The deposition of chemical reagent inks on paper is a crucial step in the development and fabrication of microfluidic paper-based analytical devices (μPADs). A pen-plotting approach, delivering chemical ink deposition using technical pens filled with reagents and inserted into a desktop electronic plotter, is shown herein to be a versatile, low-cost, simple, rapid, reproducible, and high-throughput solution. The volume of the deposited ink was quantified gravimetrically, confirming that nanoliter volumes of reagents can be deposited reproducibly (e.g. 7.55 ± 0.37 nL/mm for a plotting speed of 10 cm/s) in detection zones of μPADs, typically spatially defined using wax printing. This approach was further investigated with regard to deposition of reagents in different geometrical forms (circular and linear), so demonstrating its applicability for preparation of μPADs with flexible design and application. By adjusting the plotting speed for linear deposition, lines with a relatively large range of widths (≈628-1192 μm) were created. Circular deposition was also demonstrated via delivery of reagents within wax printed circular fluidic barriers of a range of diameters (inner diameter = 1.5-7 mm). These capabilities were practically demonstrated via the fabrication of μPADs, based upon differing detection principles for determination of aluminum in natural waters using Morin as the fluorescent reagent. Traditional μPADs based on digital image colorimetry (DIC) were produced using circular deposition, whilst distance-based μPADs exploited linear deposition. Both types of μPADs developed using this method showed excellent precision for determination of trace concentrations of aluminium (average RSDs = 3.38% and 6.45%, and LODs = 0.5 ng (0.25 ppm) and 2 ng (0.5 ppm), for traditional and distance-based detection, respectively).
Latex-Coated Polymeric Monolithic Ion-Exchange Stationary Phases. 1. Anion-Exchange Capillary Electrochromatography and In-Line Sample Preconcentration in Capillary Electrophoresis
Publisher: American Chemical Society (ACS)
Date: 07-12-2004
DOI: 10.1021/AC048748D
Abstract: A sulfonated methacrylate monolithic polymer has been synthesized inside fused-silica capillaries of diameters 50-533-microm i.d. and coated with 65-nm-diameter fully functionalized quaternary ammonium latex particles (AS18, Dionex Corp.) to form an anion-exchange stationary phase. This stationary phase was used for ion-exchange capillary electrochromatography of inorganic anions in a 75-microm-i.d. capillary with Tris erchlorate electrolyte and direct UV detection at 195 nm. Seven inorganic anions (bromide, nitrate, iodide, iodate, bromate, thiocyanate, chromate) could be separated over a period of 90 s, and the elution order indicated that both ion exchange and electrophoresis contributed to the separation mechanism. Separation efficiencies of up to 1.66 x 10(5) plates m(-1) were achieved, and the monoliths were stable under pressures of up to 62 MPa. Another latex-coated monolith in a 250-microm-i.d. capillary was used for in-line preconcentration by coupling it to a separation capillary in which the EOF had been reversed using a coating of either a cationic polymer or cationic latex particles. Several capillary volumes of s le were loaded onto the preconcentration monolith, and the analytes (inorganic anions) were then eluted from the monolith with a transient isotachophoretic gradient before being separated by electrophoresis in the separation capillary. Linear calibration curves were obtained for aqueous mixtures of bromide, nitrite, nitrate, and iodide. Recoveries of all analytes except iodide were reduced significantly when the s le matrix contained high levels of chloride. The preconcentration method was applied to the determination of iodide in open ocean water and provided a limit of detection of 75 pM (9.5 ng/L) calculated at a signal-to-noise ratio of 3. The relative standard deviation for migration time and peak area for iodide were 1.1 and 2.7%, respectively (n = 6). Iodide was eluted as an efficient peak, yielding a separation efficiency of 5.13 x 10(7) plates m(-1). This focusing was reproducible for repeated analyses of seawater.
Simultaneous separation of nitrofuran antibiotics and their metabolites by using micellar electrokinetic capillary chromatography
Publisher: Wiley
Date: 10-2006
Abstract: Mixtures comprising nitrofuran antibiotics (NFA) and nitrofuran metabolites (NFM) were resolved for the first time by using MEKC. Sodium deoxycholate (SDC) was chosen as the micelle-forming surfactant. Optimization of separation conditions was achieved by using a central composite experimental design (CCD) approach. Experimental parameters such as concentration ratio of borate to phosphate in the buffer, pH of the running electrolyte and voltage were investigated. The effect of concentration of the surfactant on resolution was significant. Under optimal conditions of 80 mM SDC, pH 9.0, (20 mM borate + 20 mM phosphate) and 16 kV, the resolution between eight consecutive peak pairs ranged from 1.9 to 11.8. Due to the absence of a UV-active chromophore in the metabolites, they were derivatized with 2-nitrobenzaldehyde (2-NBA). In order to mimic a proposed extraction procedure for the analysis of both NFA and/or derivatized NFM in a s le, aqueous s les (prederivatized with 2-NBA) were extracted by using C(18) SPE cartridges. After washing with H(2)O, the cartridges were eluted with a small portion of organic solvent with weak elution characteristics to remove excess 2-NBA (hexane was chosen). Target analytes were then recovered with ACN. Excellent reproducibility of migration time (t(mig)) was achieved for all analytes using the developed MECC approach, with absolute t(mig) <1% RSD and t(mig) ratio <0.2% RSD, and peak area ratio was 4% RSD. The LOD for each compound, calculated by extrapolating to an S/N of 3, were found to be 0.19-2.0 microg/mL.
Exploring chip-capillary electrophoresis-laser-induced fluorescence field-deployable platform flexibility: Separations of fluorescent dyes by chip-based non-aqueous capillary electrophoresis
Publisher: Elsevier BV
Date: 04-2013
DOI: 10.1016/J.CHROMA.2013.02.060
Abstract: Microfluidic chip electrophoresis (chip-CE) is a separation method that is compatible with portable and on-site analysis, however, only few commercial chip-CE systems with laser-induced fluorescence (LIF) and light emitting diode (LED) fluorescence detection are available. They are established for several application tailored methods limited to specific biopolymers (DNA, RNA and proteins), and correspondingly the range of their applications has been limited. In this work we address the lack of commercially available research-type flexible chip-CE platforms by exploring the limits of using an application-tailored system equipped with chips and methods designed for DNA separations as a generic chip-CE platform - this is a very significant issue that has not been widely studied. In the investigated Agilent Bioanalyzer chip-CE system, the fixed components are the Agilent chips and the detection (LIF at 635 nm and LEDIF at 470 nm), while the chemistry (electrolyte) and the programming of all the high voltages are flexible. Using standard DNA chips, we show that a generic CE function of the system is easily possible and we demonstrate an extension of the applicability to non-aqueous CE (NACE). We studied the chip compatibility with organic solvents (i.e. MeOH, ACN, DMF and DMSO) and demonstrated the chip compatibility with DMSO as a non-volatile and non-hazardous solvent with satisfactory stability of migration times over 50h. The generic CE capability is illustrated with separations of fluorescent basic blue dyes methylene blue (MB), toluidine blue (TB), nile blue (NB) and brilliant cresyl blue (BC). Further, the effects of the composition of the background electrolyte (BGE) on the separation were studied, including the contents of water (0-30%) and buffer composition. In background electrolytes containing typically 80 mmol/L ammonium acetate and 870 mmol/L acetic acid in 100% DMSO baseline separation of the dyes were achieved in 40s. Linearity was documented in the range of 5-28 μmol/L, 10-100 μmol/L, 1.56-50 nmol/L and 5-75 nmol/L (r(2) values in the range 0.974-0.999), and limit of detection (LOD) values were 90 nmol/L, 1 μmol/L 1.4 nmol/L, and 2 nmol/L for MB, TB, NB and BC, respectively.
Indirect photomeric detection of anions in capillary electrophoresis using dyes as probes and electrolytes buffered with an isoelectric ampholyte
Publisher: Wiley
Date: 04-2000
DOI: 10.1002/(SICI)1522-2683(20000401)21:7<1312::AID-ELPS1312>3.0.CO;2-9
Spectrophotometric study of the complexation equilibria of cadmium ions with 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-diethylaminophenol (BrPADAP, ClPADAP)
Publisher: Institute of Organic Chemistry & Biochemistry
Date: 1983
DOI: 10.1135/CCCC19830052
Abstract: The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the reactions of formation of the ML and ML 2 complexes of both reagents with cadmium(II) ions were determined by graphical analysis and numerical interpretation of the absorbance-pH curves by the modified SQUAD-G program. Optimal conditions were proposed for the spectrophotometric determination of Cd in 10% v/v ethanol medium in the presence of 0.1% w/v Triton X-100 or 1% w/v Brij 35. BrPADAP and ClPADAP are the most sensitive spectrophotometric reagents for the determination of cadmium(II) ions (ε = 1.28-1.44 . 10 5 mmol -1 cm 2 at 560 nm and pH 8.0-9.5) with a high colour contrast in the reaction (Δλ max ~117 nm) and a selectivity similar to that of other N-heterocyclic azodyes (PAR, PAN, etc. ).
Practical method for evaluation of linearity and effective pathlength of on-capillary photometric detectors in capillary electrophoresis
Publisher: Elsevier BV
Date: 08-2001
DOI: 10.1016/S0021-9673(01)01095-0
Abstract: The optical characteristics of on-capillary photometric detectors for capillary electrophoresis were evaluated and five commercial detectors were compared. Plots of sensitivity (absorbance/concentration) versus absorbance obtained with a suitable testing solution yield both the linear range and the effective path length of the detector. The detector linearity is a crucial parameter when using absorbing electrolytes, such as for indirect photometric detection, and especially for highly absorbing electrolyte probe ions. The upper limits of the linear ranges (determined as 5% decline in sensitivity) for five commercial detectors ranged from 0.175 to 1.2 AU. The effective pathlength reflects the quality of the optical design of the detector and is equal to the capillary internal diameter only for a light beam passing exactly through the capillary centre, but becomes progressively shorter for imperfect optical designs. The determined effective pathlength for the five investigated detectors ranged from 49.7 to 64.6 microm for a 75 microm I.D. capillary.
Separation of Nile Blue-labelled fatty acids by CE with absorbance detection using a red light-emitting diode
Publisher: Wiley
Date: 04-2007
Abstract: The separation of fatty acids derivatised with Nile Blue (NB) by CE with detection using a red light-emitting diode (LED) was examined. NB was selected as the derivatisation agent due to its high molar absorption coefficient of 76,000 M(-1) cm(-1) at 633 nm, making it well suited for sensitive absorbance detection using a red 635 nm LED. NB-labelled fatty acids were separated by both MEKC using SDS micelles, i-PrOH and n-BuOH and by NACE in a number of solvents including MeOH, EtOH and ACN. The sensitivity of NACE was superior to MEKC, with detection limits of 5x10(-7)-7x10(-7) M obtained for each acid, approximately 20 times lower than the MEKC method. The NACE detection limits are approximately 100 times lower than previous reports on the separation of fatty acids by CE using indirect absorbance detection, ten times lower than using indirect fluorescence detection and are inferior only to those obtained using precapillary derivatisation and direct fluorescence detection. The efficiency of the NACE method was also superior to MEKC and allowed the separation of unsaturated fatty acids to be examined, although it was not possible to baseline-resolve linoleic (C18:2) and linolenic (C18:3) acids in a reasonable time. The method was used to analyse the fatty acid profile of two edible oils, namely sunflower and sesame oils, after alkali hydrolysis, where it was possible to identify both the saturated and unsaturated fatty acids in each s le.
Trends in analytical separations of magnetic (nano)particles
Publisher: Elsevier BV
Date: 05-2019
Chemometric Approach to the Calibration of Light Emitting Diode Based Optical Gas Sensors Using High-Resolution Transmission Molecular Absorption Data
Publisher: American Chemical Society (ACS)
Date: 30-04-2018
DOI: 10.1021/ACS.ANALCHEM.8B01295
Abstract: Modeling the propagation of light from LED sources is problematic since the emission covers a broad range of wavelengths and thus cannot be considered as monochromatic. Furthermore, the lack of directivity of such sources is also problematic. Both attributes are characteristic of LEDs. Here we propose a HITRAN ( high-resolution transmission molecular absorption database) based chemometric approach that incorporates not-perfect-monochromaticity and spatial directivity of near-infrared (NIR) LED for absorbance calculations in 1-6% methane (CH
Photoinitiated polymerisation of monolithic stationary phases in polyimide coated capillaries using visible region LEDs
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B816958F
Abstract: The spatially controlled synthesis of poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic stationary phases in polyimide coated fused silica capillaries by visible light induced radical polymerisation using a three-component initiator and a 660 nm light emitting diode (LED) as a light source is presented here.
Photoswitchable stationary phase based on packed spiropyran functionalized silica microbeads
Publisher: Surface Science Society Japan
Date: 2009
Isoelectric Buffers for Capillary Electrophoresis. 2. Bismorpholine Derivative of a Carboxylic Acid as a Low Molecular Weight Isoelectric Buffer
Publisher: American Chemical Society (ACS)
Date: 30-11-2004
DOI: 10.1021/AC049237U
Abstract: A new compound class of synthetic isoelectric buffers is introduced, designed as a small molecule with one fully or prevailingly dissociated acidic group (such as sulfonic or carboxylic) and two partly pronated (buffering) basic amino groups attached onto a hydrophilic UV-transparent backbone. As an ex le, a new isoelectric compound 2,2-bis(4-morpholinylmethyl)propanoic acid (BMMPA) was synthesized by attaching two morpholine groups onto a molecule of pivalic acid. It was characterized as having an isoelectric point pI = 6.5 and exhibiting satisfactory buffering capacity at the pI. Solutions of BMMPA are transparent down to the low-UV spectral region, thus making it a potentially suitable buffer for a number of separation methods. Its use in capillary electrophoresis was demonstrated in a separation system for indirect photometric detection of anions based on an electrolyte with the anionic dye Orange G as the indirect detection probe and using BMMPA as a buffer. The use of an isoelectric buffering compound brings the advantages of a buffered electrolyte without the concomitant introduction of co-ions that would be detrimental to the indirect detection process. Submicromole per liter limits of detection for a number of inorganic and small organic ions were achieved. Optimal structural properties of the isoelectric buffer with respect to its buffering properties are discussed.
Use of coupled open-tubular capillaries for in-line ion-exchange preconcentration of anions by capillary electrochromatography with elution by a transient isotachophoretic gradient
Publisher: Elsevier BV
Date: 06-2004
DOI: 10.1016/J.CHROMA.2004.03.073
Abstract: Open-tubular capillaries have been joined together for use in on-column ion-exchange preconcentration of anions by capillary electrochromatography (CEC) with elution by a transient isotachophoretic gradient. This involved the coupling of a preconcentration capillary and a separation capillary using a PTFE sleeve. Such coupling allowed precise lengths of differently coated capillaries to be joined in-line to form a single multi-mode column. The different segments could be tailored to optimize a separation by either altering the length of each segment to precisely manipulate the amount of stationary phase present or by changing the internal diameter of each segment to alter the phase ratio in the chromatographic column without affecting the path length for UV detection. In this work, a segmented in-line capillary was used in conjunction with a fluoride-octanesulfonate discontinuous electrolyte system to increase the number of anions that could be preconcentrated and separated. Quaternary ammonium functionalised latex particles were used for creating the preconcentration segment and the separation segment was coated with poly(diallyldimethylammonium chloride). This allowed the detection of trace anions in drinking water and in situ s ling of river water for the analysis of trace inorganic anions. The repeatability of producing the quaternary ammonium functionalized latex-coated segments was assessed and the effect of segmentation on peak efficiency was investigated.
On-line preconcentration of organic anions in capillary electrophoresis by solid-phase extraction using latex-coated monolithic stationary phases
Publisher: Elsevier BV
Date: 02-2006
DOI: 10.1016/J.CHROMA.2005.08.032
Abstract: Quaternary ammonium functionalised polymeric latex particles were coated onto the wall of a fused-silica capillary or onto a methacrylate monolithic bed synthesised inside the capillary in order to create ion-exchange stationary phases of varying ion-exchange capacity. These capillaries were coupled in-line to a separation capillary and used for the solid-phase extraction (SPE), preconcentration and subsequent separation of organic anions by capillary electrophoresis. A transient isotachophoretic gradient was used for the elution of bound analytes from the SPE phase using two modes of separation. The first comprised a low capacity SPE column combined with a fluoride/octanesulfonate discontinuous electrolyte system in which peak compression occurred at the isotachophoretic gradient front. The compressed anions were separated electrophoretically after elution from the SPE preconcentration phase and resolution was achieved by altering the pH of the electrolyte in which the separation was performed. In the second approach, a latex-coated monolithic SPE preconcentration stationary phase was used in combination with a fluoride erchlorate electrolyte system, which allowed capillary electrochromatographic separation to occur behind the isotachophoretic gradient front. This method permitted the removal of weakly bound anions from the SPE phase, thereby establishing the possibility of s le clean-up. The effect of the nature of the strong electrolyte forming the isotachophoretic gradient on the separation and also on the preconcentration step was investigated. Capillary electrochromatography of inorganic and organic species performed on the latex-coated monolithic methacrylate column highlighted the presence of mixed-mode interactions resulting from the incomplete coverage of latex particles onto the monolithic surface. Analyte preconcentration prior to separation resulted in compression of the analyte zone by a factor of 300. Improvement in the limit of detection of up to 10400 times could be achieved when performing the preconcentration step and the presented methods had limits of detection (S/N=3) ranging between 1.5 and 12 nM for the organic anions studied.
Paper-based sol-gel thin films immobilized cytochrome P450 for enzyme activity measurement
Publisher: Elsevier BV
Date: 02-2020
DOI: 10.1016/J.ACA.2019.11.031
Abstract: Cytochrome P450 (CYP450), and in particular CYP3A4, is the most abundantly expressed CYP450 isozyme implicated in many drug-drug and medicinal plant-drug interactions. Therefore, incorporation of CYP3A4 enzyme screening at an early stage of drug discovery is preferable in order to avoid enzymatic interactions. Here we present for the first time a paper-based CYP3A4 immobilized sol-gel-derived a platform using resorufin benzyl ether as a fluorogenic enzyme substrate used to investigate enzyme activity. The fluorescence intensity of the product can be simply quantified by using a handheld digital microscope and an image analysis software. The limit of quantitation was 0.35 μM with good precision (RSDs 0.05), while offering simplicity and lower cost. Kinetic parameters of the immobilized CYP3A4 in sol-gel coated paper were calculated from the Lineweaver-Burk plot, including Michaelis constant (K
Modelling and optimization of the electrokinetic chromatographic separation of mixtures of organic anions and cations using poly(diallydimethyl- ammonium chloride) and hexanesulfonate as mixed pseudos
Publisher: Wiley
Date: 09-2002
DOI: 10.1002/1522-2683(200209)23:17<2821::AID-ELPS2821>3.0.CO;2-L
Comparison of Different Contactless Conductivity Detectors for the Determination of Small Inorganic Ions by Capillary Electrophoresis
Publisher: Wiley
Date: 07-2006
Abstract: The analytical performance parameters of four different contactless conductivity detectors for capillary electrophoresis were determined. These detectors were designed either with a miniature cell for versatility, with high voltage excitation for high sensitivity or with a battery power supply for field application. One of the units is commercially available. The plate numbers and reproducibility of peak areas (typically about 2%) were very similar, indicating that these parameters are generally limited by the separation and injection procedures rather than the detectors. The linear dynamic ranges are better than 2 orders of magnitude for all detectors and the correlation coefficients were also almost identical. Significant differences were found with regard to the detection limits. For the detector with a miniature cell, which lacks an in‐cell lifier, the detection limit was typically 1.5 μM for the inorganic ions tested (K + , Ca 2+ , Na + , Mg 2+ , Li + , Cl − , NO 3 − and SO 4 2− ), while with the other 3 detectors this parameter was as low as about 0.1 μM. The use of buffer solutions with relatively high background conductivity was found to lead to detection limits which were up to one order of magnitude higher. The extent of deterioration of this parameter with buffer conductivity was found to be related to the excitation voltage and was most pronounced for the high voltage detector.
Poly(tetrafluoroethylene) separation capillaries for capillary electrophoresis
Publisher: Elsevier BV
Date: 06-2004
DOI: 10.1016/J.CHROMA.2004.03.074
Abstract: Poly(tetrafluoroethylene) (PTFE) is a material widely known for its inertness and excellent electrical properties. It is also transparent in the UV region and has a reasonable thermal conductivity. These properties make PTFE a suitable material for the separation capillary in capillary electrophoresis. Differences in the chemistry of the capillary wall compared to fused silica (FS) can make PTFE an interesting alternative to FS for some special applications. In this work, properties of a commercial PTFE capillary of approx. 100 microm i.d. were investigated, including the dependence of electroosmotic flow (EOF) on pH for unmodified and dynamically modified PTFE, optical properties, and practical aspects of use. The main problems encountered for the particular PTFE capillary used in this study were that it was mechanically too soft for routine usage and the crystallinity of the PTFE caused light scattering, leading to high background absorbance values in the low UV region. The profile of the EOF versus pH for bare PTFE surprisingly showed significantly negative EOF values at pH < 4.2, with an EOF of -30 x 10(-9) m2 V(-1) s(-1) being observed at pH 2.5. This is likely to be caused by either impurities or additives of basic character in the PTFE, so that after their protonation at acidic pH they establish a positive charge on the capillary wall and create a negative EOF. A stable cationic semi-permanent coating of poly(diallyldimethylammonium chloride) (PDDAC) could be established on the PTFE capillary and led to very similar magnitudes of EOF to those observed with FS. A hexadecanesulfonate coating produced a cathodic EOF of extremely high magnitude ranging between +90 and +110 x 10(-9) m2 s(-1) V(-1), which are values high enough to allow counter-EOF separation of high mobility inorganic anions. In addition, pH-independent micellar electrokinetic capillary chromatography (MEKC) separations could be easily realised due to hydrophobic adsorption of sodium dodecylsulfate (used to form the micelles) on the wall of the PTFE capillary. The use of polymers that would be mechanically more robust and optically transparent in the low-UV region should make such CE capillaries an interesting alternative to fused silica.
One step multi-material 3D printing for the fabrication of a photometric detector flow cell
Publisher: Elsevier BV
Date: 02-2020
DOI: 10.1016/J.ACA.2019.10.075
Abstract: Optical detection is the most common detection mode for many analytical assays. Photometric detection systems and their integration with analytical systems usually require several assembly parts and manual alignment of the capillary/tubing which affects sensitivity and repeatability. 3D printing is an innovative technology for the fabrication of integrated complex detection systems. One step multi-material 3D printing has been explored to fabricate a photometric detector flow cell from optically transparent and opaque materials using a dual-head FDM 3D printer. Integration of the microchannel, the detection window and the slit in a single device eliminates the need for manual alignment of fluidic and optical components, and hence improves sensitivity and repeatability. 3D printing allowed for rapid design optimisation by varying the slit dimension and optical pathlength. The optimised design was evaluated by determining stray light, effective path length and the signal to noise ratio using orange G. The optimised flow cell with extended path length of 10 mm and 500 μm slit yielded 0.02% stray light, 89% effective path length and detection limit of 2 nM. The sensitivity was also improved by 80% in the process of optimisation, using a blue 470 nm LED as a light source.
Determination of inorganic anions by capillary electrochromatography
Publisher: Elsevier BV
Date: 06-2001
Isotachophoresis for rapid transformation of Escherichia coli
Publisher: Wiley
Date: 21-12-2022
Abstract: A frequent limitation of electroporation (EP) and chemical transformation (CT) are the need of tedious and time‐consuming procedures for inducing transformation competence, the substantial number of cells required, and the low transformation yields typically achieved. Here, we show a new and rapid electrokinetic method for transformation of small number of noncompetent Escherichia coli TOP10 cells (2–3 × 10 5 ) at room temperature. Escherichia coli TOP10 cells and plasmid DNA are sequentially injected into a 50 μm ID capillary and focused into 11.5 nL by isotachophoresis (ITP) induced by application of high DC voltage (–16 kV). Through ITP, a large excess of plasmid DNA is brought in contact with the cell surface, with the contact time adjusted by application of a counter‐pressure (1.3 psi) opposing the ITP movement. The transformation rate was more than 1000‐fold higher compared to EP and CT at survival rates greater than 60%.
Paperfluidic devices with a selective molecularly imprinted polymer surface for instrumentation-free distance-based detection of protein biomarkers
Publisher: Elsevier BV
Date: 08-2021
Potential of Capillary Electrophoresis (CE) and Chip-CE with Dual Detection (Capacitively-Coupled Contactless Conductivity Detection (C4D) and Fluorescence Detection) for Monitoring of Nicotine and Co
Publisher: Springer Science and Business Media LLC
Date: 03-2013
Abstract: Capillary electrophoresis (CE) coupled with capacitively-coupled contactless conductivity (C(4)D) and fluorescence (FD) detectors and chip-CE for monitoring of nicotine and cotinine derivatization was demonstrated. Separation of the substrates and intermediates could be achieved by CE-C(4)D in 7 min (R(s) > 2.7) using 45 mM acetic acid (pH 3.0) and this system was applied to detect the intermediate formation. Final fluorescent products could be analyzed by micellar electrokinetic chromatography (MEKC-FD) in 5 mM borate buffer (pH 9.0) containing 10 mM sodium dodecylsulfate (SDS) (%RSD < 3.00%). Transferring of MEKC-FD to chip-CE allowed for shorter analysis time (2.5 min) and decreased s le consumption. The chip-CE-FD shows good detection and quantitation limits (< 7.5 µM) and precision (%RSD < 2.81%) and was employed to determine nicotine and cotinine in artificial urine. This work reveals the potential of CE and chip-CE with dual detectors as simultaneous, convenient and rapid methods for monitoring pyridine derivatization.
Simultaneous separation of inorganic anions and cations using capillary electrophoresis with a movable contactless conductivity detector
Publisher: Royal Society of Chemistry (RSC)
Date: 30-04-2002
DOI: 10.1039/B202765H
Abstract: A number of small inorganic anions and cations were separated after injection of the s le into both ends of a separation capillary. The ions were detected using a capacitively coupled contactless conductivity detector (CCCCD) which could be placed at various positions along the capillary length. Counter-directional migration of anions and cations occurs towards the detector, which is placed at an appropriate position along the capillary so that the migration order is determined by the respective effective separation capillary lengths for both anions and cations. As the CCCCD detector can be easily moved to any position along the capillary, virtually any effective separation length can be attained. Depending on the number of analytes in the s le, one can choose to obtain either electropherograms with inter-migrating zones of cations and anions or separations with distinct regions of anion and cation zones, respectively. A new term 'apparent separation selectivity' is introduced to describe the manner in which the position of the detector can be varied in order to determine the final separation.
Chip-based CE for rapid separation of 8-aminopyrene-1,3,6-trisulfonic acid (APTS) derivatized glycans
Publisher: Wiley
Date: 22-10-2010
Abstract: Fluorescently labeled carbohydrates released from glycoproteins were separated using a commercially available microfluidic chip electrophoresis system. While the instrumentation was primarily designed for DNA analysis it was found that the application base can be easily expanded using the development software provided by the manufacturer. The carbohydrates were released by enzymatic digestion (PNGase F) from glycoproteins present in human plasma after boronic acid - lectin affinity enrichment. After fluorescent labeling with 8-aminopyrene-1,3,6-trisulfonic acid the carbohydrates were separated based on capillary gel electrophoresis mechanism and detected by a fluorescence detector using a blue (470 nm) LED. The separation was completed in 40 s in a microfluidic channel of 14 mm length. Glucose ladder carbohydrate oligomers differing by one glucose unit were baseline separated up to a 20-mer with the main limitation being the detection sensitivity. As expected, the observed resolution in these experiments did not approach that of standard CE with 20 times longer separation distance however, the chip-based analysis excelled in the speed of the separation. Similar electrophoretic profiles of glycans released from plasma glycoproteins were obtained using a standard CE equipment with 35 cm separation length and microfluidic chips with a separation distance of only 14 mm.
Non-aqueous capillary electrophoresis with red light emitting diode absorbance detection for the analysis of basic dyes
Publisher: Elsevier BV
Date: 11-2006
DOI: 10.1016/J.ACA.2006.07.066
Abstract: Non-aqueous capillary electrophoresis was evaluated for the separation of five hydrophobic basic blue dyes for application in forensic dye analysis. The use of a red light emitting diode as a high intensity, low-noise light source provided sensitive detection of the blue dyes while also allowing the evaluation of solvents that absorb strongly in the UV region. Excellent peak shapes and separation selectivity were obtained in methanol, ethanol, acetonitrile and dimethylsulfoxide, however water, tetrahydrofuran, dimethylformamide and acetone were unsuitable as solvents due to poor peak shapes and a lack of sensitivity, most likely due to adsorption onto the capillary wall. Due to the known compatibility of methanol with capillary electrophoresis-mass spectrometry, this solvent was examined further with the relative acidity/basicity of the electrolyte being optimised with an artificial neural network. The optimised method was examined for the separation of ink s les from 6 fibre tip and 2 ball point blue or black pens and showed that a unique migration time for the main dye component in seven of the eight pens could be obtained.
Miniaturised medium pressure capillary liquid chromatography system with flexible open platform design using off-the-shelf microfluidic components
Publisher: Elsevier BV
Date: 10-2015
DOI: 10.1016/J.ACA.2015.09.015
Abstract: Trends towards portable analytical instrumentation of the last decades have not been equally reflected in developments of portable liquid chromatography (LC) instrumentation for rapid on-site measurements. A miniaturised medium pressure capillary LC (MPLC) system with gradient elution capability has been designed based on a flexible modular microfluidic system using primarily off-the-shelf low cost components to ensure wide accessibility to other analysts. The microfluidic platform was assembled on a breadboard and contained microsyringe pumps and switch valves, complemented with an injection valve and on-capillary detectors, all controlled by a PC. Four miniaturised microsyringe pumps, with 5, 20 and 100 μL syringe volume options, formed the basis of the pumping system. Two pairs of pumps were used for each mobile phase to create gradient elution capability. The two microsyringe pumps in each pairs were linked by two electrically operated microfluidic switching valves and both pairs of pumps were connected through a zero void volume cross-connector, thus providing a low hold-up volume for gradient formation. S le was injected by a 20 nL nano-LC s ling valve, directly connected to a 18 cm long 100 μm i.d. Chromolith CapRod RP-18 monolithic capillary column. On-capillary LED-based UV-vis photometric detection was conducted through a piece of equal diameter fused silica capillary connected after the column. The performance of the portable LC system was evaluated theoretically and experimentally, including the maximum operating pressure, gradient mixing performance, and the performance of the detectors. The 5 μL microsyringe pump offered the best performance, with typical maximum operating pressures up to 11.4 ± 0.4 MPa (water) and gradient pumping repeatability of between 4 and 9% for gradients between 0.10% s(-1) and 0.33% s(-1). Test analytes of charged and uncharged dyes and pharmaceuticals of varying hydrophobicity showed typical RSD values of 0.7-1.4% and 3.3-4.8% in isocratic mode and 1.2-4.6% and 3.2-6.4% in gradient mode, respectively for retention time and peak area repeatability.
Highly sensitive indirect photometric detection of cations by capillary electrophoresis with the cationic dye chrysoidine
Publisher: Elsevier BV
Date: 05-2003
DOI: 10.1016/S0021-9673(03)00062-1
Abstract: The cationic dye, chrysoidine, has been used for the first time as a probe for the indirect photometric detection of cations. The dye has been used as a probe at concentrations of 5 mM, which is roughly an order of magnitude higher than for other cationic dyes used previously for the same purpose, in order to minimise electromigrational dispersion. Baseline instability was minimised by a combination of coating the capillary with poly(ethyleneimine), addition of a neutral polymer to the electrolyte, and the application of a small amount (20 mbar) of hydrodynamic pressure during the separation. Separation of a mixture containing alkali metals, alkaline earths, transition metals and lanthanides was achieved by the addition of 2-hydroxyisobutyric and lactic acid as complexing agents. Excellent peak shapes were observed over a wide range of analyte mobilities due to the moderate mobility of the probe. The high absorptivity (26733 l mol(-1) cm(-1)) provided by chrysoidine in comparison with typically used, less absorbing probes, was reflected in limits of detection which were typically less than 0.5 microM. These are amongst the lowest reported using hydrodynamic injection without the use of large volume stacking methods. The use of 2-hydroxyisobutyric and lactic acids as complexing agents at pH values close to their pKa values provided suitable buffering which was highlighted by very good reproducibility of migration time, corrected peak area and peak height.
Development of a contactless conductivity detector cell for 1.6 mm O.D. (1/16th inch) HPLC tubing and micro-bore columns with on-column detection
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B803038C
Abstract: A capacitively coupled contactless conductivity detector cell was designed and constructed suitable for standard HPLC 1.6 mm o.d. (1/16'') tubing and columns. Bode plots were acquired in order to determine the optimum input frequency for the new detector cell, with three feedback resistors of increasing resistance (1 MOmega, 3.3 MOmega and 4.7 MOmega) alternately fitted to maximize sensitivity. To evaluate the new detector geometry, a 190 mm x 0.381 mm i.d. (1.59 mm o.d.) column packed with Dionex OmniPac 8.5 microm PAX-100 anion exchange resin was used, with an eluent of 0.5 mM sodium benzoate containing 2% methanol, pumped at 20 microL min(-1), with detection taking place 'on-column'. Standard analytical performance criteria were used to compare the test detector with a commercially available TraceDec C(4)D capillary (360 microm o.d.) detector, with the new detector cell matching the performance of the commercial instrument in terms of linearity, sensitivity and reproducibility. In 'on-column' detection mode, the detector cell could be moved during (or between) chromatographic runs along the length of the packed column bed, to shorten the effective length of the column and thus reduce the retention time of strongly retained s le components, whilst maintaining the resolution of weakly retained components. In addition, the detector could also be applied to the evaluation of the stationary phase packing homogeneity by physically scanning the entire length of the micro-bore column with the moveable detector cell.
Modelling, optimisation and control of selectivity in the separation of aromatic bases by electrokinetic chromatography using a neutral cyclodextrin as a pseudostationary phase
Publisher: Wiley
Date: 06-2002
DOI: 10.1002/1522-2683(200206)23:12<1844::AID-ELPS1844>3.0.CO;2-9
Tags, tagging, tagged, # - undisciplining organ-ization of [academic] bodies
Publisher: Informa UK Limited
Date: 18-04-2023
Miniaturized LC in Molecular Omics
Publisher: American Chemical Society (ACS)
Date: 12-08-2020
Related Organisations
University Of Tasmania Faculty Of Science Engineering And Technology
Location: Australia
Related Funding Activities
Discovery Projects - Grant ID: DP0662838
Start Date: 2006
End Date: 12-2010
Amount: $225,000.00
Funder: Australian Research Council
View Funded ActivityLinkage Projects - Grant ID: LP120200079
Start Date: 05-2013
End Date: 12-2017
Amount: $210,000.00
Funder: Australian Research Council
View Funded ActivityARC Future Fellowships - Grant ID: FT120100559
Start Date: 12-2012
End Date: 12-2019
Amount: $901,168.00
Funder: Australian Research Council
View Funded ActivitySpecial Research Initiatives - Grant ID: SR0354560
Start Date: 01-2004
End Date: 12-2004
Amount: $10,000.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE0668471
Start Date: 2006
End Date: 12-2006
Amount: $262,706.00
Funder: Australian Research Council
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