ORCID Profile
0000-0002-8275-9672
Current Organisation
University of Tasmania
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Elsevier BV
Date: 2009
DOI: 10.1016/J.CHROMA.2008.11.062
Abstract: The direction of the effective electrophoretic mobility of small organic cations in micellar electrokinetic chromatography using sodium dodecyl sulphate in a low-pH electrolyte can be reversed in the presence of organic solvent. This effective electrophoretic mobility change is presented here as a new dimension for on-line s le preconcentration of cations in capillary zone electrophoresis (CZE) using a background solution (BGS) modified by an organic solvent. The s le is prepared in a micellar solution without organic solvent. The focusing effect relies on the reversal in the effective electrophoretic mobility at the boundary zone between the micellar matrix and the BGS modified with organic solvent. This on-line s le preconcentration technique, called micelle to solvent stacking (MSS) afforded more than an order of magnitude improvement in concentration sensitivity compared to typical CZE-UV or CZE-electrospray ionization (ESI) MS analysis. The calculated limit of detection (S/N=3) for pindolol and metoprolol analysed by MSS-CZE-ESI-MS was found to be 0.03 and 0.01 microg/mL, respectively.
Publisher: Elsevier BV
Date: 04-2016
DOI: 10.1016/J.CHROMA.2016.03.002
Abstract: Three-step stacking by field-enhanced s le injection (FESI), sweeping, and micelle to solvent stacking (MSS) in co-EOF capillary zone electrophoresis (CZE) is presented for anionic analytes. Long FESI produced an overloaded stacked zone of analytes (four model penicillins). Sweeping of the FESI zone was by electrokinetic injection of cetyltrimethylammonium bromide (CTAB) micelles. MSS was by short injection of 60% methanol that released the swept analytes from CTAB micelles. The sensitivity enhancement factors were 146-279 and 519-954 for conductivity ratio of 10 and 100, respectively. The SEF enhancement factors (factor=SEF from three-step stacking/SEF from FESI) were 16-32 and 6-10, correspondingly. The LODs were between 6.6-13.2 ng/mL, repeatability (intraday and interday) was %RSD≤5.4%, and linearity was R(2)≥0.998. Application to real s le was investigated using fortified plasma after liquid-liquid extraction.
Publisher: Wiley
Date: 2013
Abstract: CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field lified s le stacking and large volume s le stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.
Publisher: Elsevier BV
Date: 07-2011
DOI: 10.1016/J.TALANTA.2011.03.032
Abstract: The simultaneous analysis of tricyclic antidepressant (amitriptyline, clomipramine, doxepin and nortriptyline) and β-blocker (alprenolol, labetalol and propranolol) drugs in wastewater was developed via sweeping-micellar electrokinetic chromatography (MEKC) together with a simple liquid-liquid extraction step. For sweeping-MEKC, the amount of organic modifier in the separation electrolyte, the concentration of phosphoric acid in the s le matrix and the injection time of the s le were optimized. Sensitivity enhancements of up to 305-fold were achieved via sweeping. This allowed limits of detection (LOD) from 7 to 27 ng/mL. The relative standard deviations of migration time, corrected peak area and peak height were less than 3.2%, 7.8% and 4.5%, respectively. Liquid-liquid extraction using dichloromethane as solvent afforded up to 21-fold enrichment of the drugs from spiked wastewater. No interference of the s le matrix was observed and recoveries were obtained in the range of 77-113% for all analytes except labetalol at three spiking levels of 16, 80 and 160 ng/mL. Detection at the ng/mL level makes this simple, environmentally friendly and cost effective method competitive against recently reported methods using advanced liquid-phase separation techniques for monitoring similar drugs in wastewater.
Publisher: Elsevier BV
Date: 11-2021
Publisher: Springer Science and Business Media LLC
Date: 23-06-2023
DOI: 10.1007/S00216-023-04798-1
Abstract: Silica nanospheres (SNS) were grown on the inner walls of silica capillaries through a dynamic in situ nucleation process to prepare a highly porous and large accessible surface area substrate. The SNS were then functionalized with octadecyl (C 18 ), 3-aminopropyltriethoxysilane (APTES), beta-cyclodextrin ( β -CD), and amino groups to develop robust and efficient chromatographic stationary phases. The modified silica capillaries were exploited for open-tubular liquid chromatography (OT-LC) and open-tubular capillary electrochromatography (OT-CEC) applications. The prepared stationary phases were compared to conventional capillaries in terms of separation performance. The synthesis process was optimized, and the bonded-phase stationary phases were characterized by the electron microscopy technique. The effects of different solvents, additives, and functional groups on the geometry and chromatographic resolving power of the SNS were envisaged. The capillaries modified with octadecyl groups were evaluated for the separation of non-steroidal anti-inflammatory drugs, phenones, alkenylbenzenes, and enantiomers of chlorophenoxy herbicides. As an application instance, an SNS-C 18 -coated capillary was utilized for the separation of alkenylbenzenes from clove extract and protein digest medium, through OT-LC and OT-CEC techniques, respectively. The β -CD functionalized capillary was applied for the OT-CEC separation of a dichlorprop racemic mixture. Graphical abstract
Publisher: Wiley
Date: 17-11-2015
Abstract: Derivatisation is a well-established and mature form of s le preparation for CE. The modification of the analyte can cause superior analysis characteristics such as better sensitivity and selectivity, however, derivatisation of the analyte introduces an additional step into the analytical workflow. This review covers articles from January 2012 to January 2015 on derivatisation in CE. The main sections are on the derivatisation modes (i.e. pre-capillary, in-line, in-capillary and post-capillary), separation and detection modes (i.e. LIF and others). LIF is discussed in more detail since this detection mode was most prevalent. A table of the common labelling agents and wavelengths for excitation and emission and the common derivatisation reactions are included. In addition, a comprehensive table which summarises all research articles is provided. This review is suitable for analytical chemists as a guide for 'how to get started' with derivatisation for separation and detection in CE.
Publisher: American Chemical Society (ACS)
Date: 29-01-2000
DOI: 10.1021/AC990344B
Abstract: A novel method that combines two on-line concentration techniques in capillary electrophoresis (CE), namely, s le stacking with electrokinetic injection (field-enhanced s le injection, FESI) and sweeping, afforded the detection of positively chargeable analytes in parts per trillion (ppt) levels. The main idea is to selectively introduce by FESI as many molecules of cationic analytes as possible from a very dilute s le solution and focus the resulting zone by sweeping. Limit of detection values (signal-to-noise ratio 3) of 4.1 and 8.0 ppt-the lowest concentration reported by direct UV detection in CE-with average plate numbers of 3.6 x 10(5) and 4.4 x 10(5) are obtained for laudanosine and naphthylamine (standard solutions), respectively. This translates to improvements in peak heights compared with usual injection approaching a million-fold. Optimization schemes and application to quantitative and qualitative analyses are also investigated.
Publisher: Wiley
Date: 28-11-2011
Abstract: Online s le concentration or stacking of basic drugs by transient isotachophoresis with the injection of an acid in co-electroosmotic flow capillary zone electrophoresis was studied experimentally and with computer simulation. The acid stacking strategy afforded an order of magnitude improvement in concentration sensitivity for model tricyclic antidepressant and β blocker drugs.
Publisher: Elsevier BV
Date: 09-1999
DOI: 10.1016/S0021-9673(99)00836-5
Abstract: The important features of electrokinetic chromatography are critically reviewed. Special emphasis is given to systems using micelles as pseudostationary phase. Short and comprehensive overviews are given on the subjects of separation, comparison with capillary electrochromatography, on-line coupling with mass spectrometry, and developments that are expected in the future. A greater coverage on the subject of improvement of detection sensitivity, specifically by on-line concentration was also contributed.
Publisher: Wiley
Date: 02-2011
Abstract: Transient trapping is a new mechanism of on-line s le concentration and separation that has recently been presented. It involves the injection of a short length of micellar solution in front of the s le, making it similar to sweeping in partial-filling MEKC. Here, we examine the mechanism of transient trapping by the use of computer simulations and compare it to sweeping in MEKC for the two analytes, sulforhodamine B and 101. The simulation results confirm the mechanism for concentration and separation originally proposed. The mechanism for concentration is similar to sweeping since the analytes are picked and accumulated by the micelles that penetrate the s le zone. The mechanism for separation is however quite unique since the concentrated analytes are trapped for a few seconds on the s le/micelle boundary before they are released as the concentration of micelle is reduced as it undergoes electromigration dispersion and the analytes separate down a micelle gradient. Simulation results suggested that a significant contribution of band broadening arises from the micelle gradient, with shallower gradients resulting in broader peaks. However, this is offset by an increase in selectivity, such that resolution was enhanced even though the peaks are broader. Transient trapping analysis with similar resolution to those obtained by sweeping MEKC could be achieved in 1/10 of the time and 1/4 of the capillary length, which results in a 2-3 times increase in sensitivity.
Publisher: Elsevier BV
Date: 07-2014
DOI: 10.1016/J.CHROMA.2014.05.007
Abstract: A synergistic stacking approach whereby field-enhanced s le injection and micelle-to-solvent stacking in capillary zone electrophoresis are combined has been developed and has been applied to the separation and quantification of anionic sulfonamides. Electrokinetic injection of the s le in a low conductivity alkaline diluent was performed for 90s at -15kV. Micelle-to-solvent stacking was then undertaken by hydrodynamic injection of micellar cetyltrimethylammonium bromide solution prior to the electrokinetic injection of s le that also contained 50% methanol. This combined stacking approach, when compared to a typical hydrostatic injection, provided improvements in peak height and corrected peak area in the range of 397-1024 and 758-1246, respectively. Limits of quantification in the range of 0.01-0.03μg/mL were obtained for sulfamerazine, sulfamethazine and sulfamethizole and were sufficient for the determination of these analytes in river water. The percentage recovery and accuracy values obtained for a fortified river water s le that had been subjected to s le preparation by evaporation and reconstitution with diluent were 74-135%. Intra-day and inter-day repeatabilities for migration time, peak height, and corrected peak area were in the range 0.5-5.0% (percentage relative standard deviation, n=8) and these relatively low values were attributed to the use of a stable capillary coating established by the successive multiple ionic-polymer layer technique.
Publisher: American Chemical Society (ACS)
Date: 19-02-2002
DOI: 10.1021/AC0104173
Abstract: In this study, a deuterium exchange procedure has been employed to evaluate the thermal stability of globular proteins under conditions that replicate their interactive behavior in reversed-phase high performance chromatographic (RP-HPLC) systems. In particular, this investigation has permitted the conformational stability of two proteins, hen egg white lysozyme (HEWL) and horse heart myoglobin (HMYO) to be examined under different temperature and low-pH solvent regimes. The results confirm that this experimental approach provides an efficient strategy to explore fundamental conformational features of polypeptides or proteins in their folded and partial unfolded states under these interactive conditions. In particular, this analytical procedure permits insight to be readily gained into the processes that occur when polypeptides and globular proteins interact with lipophilic liquid/ solid interfaces in the presence of water-organic solvent mixtures at different temperatures.
Publisher: Elsevier BV
Date: 04-2018
DOI: 10.1016/J.ACA.2017.12.012
Abstract: Sodium dodecyl sulfate (SDS) removal is a vital procedure in SDS-assisted bottom-up proteomics because SDS affects the quality of the data in electrospray ionization mass spectrometry (ESI-MS). SDS removal methods provide efficient removal of SDS and improved peptide analysis, but would usually require time, specialised devices, and experienced analysts. Here, by simple addition of γ-cyclodextrin (γ-CD) to the solution at concentrations 1 to 2x the SDS in the s le, the SDS related signals in positive ionization ESI-MS can be significantly removed (70-99% reduction), without an additional s le manipulation step of extraction or purification. The mechanism for removal is based on the formation of tightly bound CD-SDS inclusion complexes, which h ered the generation of positively charged SDS multimers during ESI. For a s le with peptides (glu-val-phe, tyr-tyr-tyr, and bradykinin) and 3 mM SDS where 6 mM γ-CD was added, the %signal recoveries of peptides calculated by comparison with signals from standard s les without SDS were 49-59%. The space charge effect by SDS on bradykinin was also reduced, increasing the signal for bradykinin 12x in the presence of γ-CD. For a protein (bovine serum albumin, BSA) digest with 3 mM SDS, which is an expected concentration in trypsin treated s les, a noticeable 7-fold improvement in the peptide to SDS signal ratio and a 91% reduction of SDS signals were observed upon addition of 6 mM γ-CD. However, there were only small changes in the ESI-MS intensities for the BSA peptides (compared to without addition of γ-CD). This new approach to SDS signal removal using CDs in ESI-MS may find use in proteomic studies.
Publisher: Elsevier BV
Date: 06-2016
Publisher: Wiley
Date: 2016
Abstract: Open tubular CEC (OT-CEC) separates analyte mixtures by a combination of electrophoretic, electro-osmotic, and/or chromatographic effects. OT-CEC research is an active and growing field, with studies encompassing a wide range of investigations related to new strategies for chemical modification of the inner surface of the capillary, leading to the introduction of novel stationary phase coatings. This review has examined the literature on OT-CEC from 2013 to August 2015 and highlights the developments in the fabrication of highly selective stationary phases, based on materials that include cyclodextrin chiral selectors, graphene and graphene oxide, metal-organic frameworks, molecularly imprinted polymers, nanoparticles, nanolatex particles, nanocomposites, in situ generated polymers, block polymers, tentacle-type polymers, polyelectrolyte multilayers, polysaccharides, phospholipids, and proteins. This review, while considering the development of novel OT-CEC coating materials, specifically examines different immobilization or coating methodologies and approaches and also discusses the separation mechanisms that occur with these new materials. These OT-CEC coatings are intended mainly to separate low molecular weight molecules relevant to the pharmaceutical, agricultural, and food industries as well as for use in environmental monitoring.
Publisher: American Chemical Society (ACS)
Date: 08-12-2017
DOI: 10.1021/ACS.ANALCHEM.7B03700
Abstract: A stacking approach in capillary electrophoresis based on the reversal of the analytes' effective electrophoretic velocities at a dynamic stacking boundary formed between charged micelles (i.e., from long chain ionic surfactants) and neutral cyclodextrins (i.e., native α-, β-, or γ-cyclodextrin) is presented. The approach was demonstrated by the long injection of s les in a micellar solution followed by injection of a cyclodextrin solution zone, and then separation by co-electro-osmotic flow capillary zone electrophoresis. The reversal is caused by the formation of stable cyclodextrin-surfactant complexes at the boundary that significantly decreased the retention factor of the analytes in the presence of a micellar pseudostationary phase. The dynamic boundary was formed at the cyclodextrin zone as the micelles penetrated this zone. Under optimum conditions, the boundary disappears, and the stacking ends when all the micelles have electrophoretically migrated to the boundary. Cationic and anionic small molecules were enriched using oppositely charged micelles from sodium dodecyl sulfate and cetyltrimethylammonium bromide, respectively. There were 1-2 orders of concentration magnitude improvement in analyte detection, which is expected in stacking with hydrodynamic injection. The improvements in the peak signals (height/corrected area) were up to 236/445 and 101/76 for the cationic and anionic analytes tested, respectively. Linearity (r
Publisher: Wiley
Date: 07-2012
Abstract: In this paper, by injecting a SDS micellar plug before the s le prepared in aqueous organic solvents, we show the on-line s le preconcentration of cations via micelle to solvent stacking (MSS) using solvents of as low as 30%. This extends the choice of stacking techniques to include moderate amounts of organic solvent in the s le. The approach is akin to in-line solid phase extraction where the micellar plug acted as a transient micellar phase extractor. Basic studies were conducted (e.g. type and amount of organic solvent in the s le). The calculated sensitivity enhancement factors based on LOD obtained for the six test antipsychotic drugs were from 41 to 68. The peak signals were linear (R² > 0.99) from 0.2 to 10.0 μg/mL. The intraday and interday reproducibility (n = 10) for migration time, peak height, and corrected peak area were from 0.2 to 13.6%. The technique was also tested on spiked wastewater s le with minimal s le treatment (i.e. dilution and centrifugation).
Publisher: Elsevier BV
Date: 12-2012
DOI: 10.1016/J.CHROMA.2012.10.026
Abstract: The isotachophoretic analysis of different bacterial strains was studied using capillaries with different internal diameters from 50 to 250 μm. Several injection modes were investigated and compared in order to improve the limit of detection of bacteria by capillary isotachophoresis. A system suitability test obtained from the separation voltage was developed to ensure reliable results. As expected, the use of wider bore capillaries improved the analytical sensitivity of the isotachophoretic method when compared to the 50 μm capillary. With the optimized conditions, the isotachophoretic method presented in this work allows the quantification of Erwinia carotovora (Gram negative bacteria) with a limit of detection as low as ~3000 cells mL(-1). The proposed methodology does not require any additive in the electrolyte such a fluorescent or chromophoric dye to reach these limits of detection.
Publisher: Elsevier BV
Date: 08-2022
DOI: 10.1016/J.CHROMA.2022.463383
Abstract: We present pseudophase-to-solvent microextraction (PSME) as a simple pressure-driven in-line s le concentration technique in capillary zone electrophoresis (CZE) for small organic anions. The developed technique is like solid-phase extraction however, the chromatographic phase is a pseudophase, i.e., in-situ cetyltrimethylammonium bromide (CTAB) interfacial micelles. A large volume of s le (e.g., > 12 capillary volumes) prepared in [CTAB] ∼critical micelle concentration was injected into the capillary. The elution and enrichment of analytes trapped in the CTAB coating was facilitated by the high concentration of methanol in the background solution, which was introduced from the outlet end. Co-electroosmotic flow CZE was conducted after the concentrated analytes reached the tip of the inlet. Parameters such as s le loading time and elution time were optimised. Under optimised conditions, the SEFs of 187-573 achieved for the model anions (4-nitrophenol, 4-vinylbenzoic acid, mecoprop, indoprofen, sulfamethizole and sulindac) were comparable to previously reported off-line microextraction techniques. The calculated LOD (S/N = 3), LOQ (S/N = 10), intra-/inter- (n = 6/n = 9, 3 days) day repeatability and linearity (R
Publisher: Wiley
Date: 02-2009
Abstract: The electrophoresis simulation software, GENTRANS, has been modified to include the interaction of analytes with an electrolyte additive to allow the simulation of liquid-phase EKC separations. The modifications account for interaction of weak and strong acid and base analytes with a single weak or strong acid or base background electrolyte additive and can be used to simulate a range of EKC separations with both charged and neutral additives. Simulations of separations of alkylphenyl ketones under real experimental conditions were performed using mobility and interaction constant data obtained from the literature and agreed well with experimental separations. Migration times in fused-silica capillaries and linear polyacrylamide-coated capillaries were within 7% of the experimental values, while peak widths were always narrower than the experimental values, but were still within 50% of those obtained by experiment. Simulations of sweeping were also performed although migration time agreement was not as good as for simple EKC separations, peak widths were in good agreement, being within 1-50% of the experimental values. All simulations for comparison with experimental data were performed under real experimental conditions using a 47 cm capillary and a voltage of 20 kV and represent the first quantitative attempt at simulating EKC separations with and without sweeping.
Publisher: Elsevier BV
Date: 12-2010
DOI: 10.1016/J.CHROMA.2010.10.020
Abstract: Two-step stacking of organic cations by sweeping and micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) is presented. The simple procedure involves hydrodynamic injection of a micellar sodium dodecyl sulfate solution before the s le that is prepared without the micelles. The micelles sweep and transport the cations to the boundary zone between the s le and CZE buffer. The presence of organic solvent in the CZE buffer induces the second stacking step of MSS. The LODs obtained for the four beta blocker and two tricyclic antidepressant test drugs were 20-50 times better compared to typical injection.
Publisher: Elsevier BV
Date: 11-2000
DOI: 10.1016/S0021-9673(00)00812-8
Abstract: The behavior of charged species along concentration boundaries in capillary zone electrophoresis (CZE) that was first described in detail by Everaerts et al. in 1979 assured the possibility of concentrating charged solutes inside the capillary. The concentration effect is based on the sudden change in analyte electrophoretic velocity brought about by the difference in the magnitude of the electric field. Furthermore, this on-line method could be the needed solution to the problem of low concentration sensitivity in CZE. S le stacking, which is now its well known name, has then found valuable use in applying CZE in many fields, especially after the in-depth studies performed in the early 90s by Chien and Burgi. This article reviews the theory and methodological developments of s le stacking developed for charged analytes in CZE and also in electrokinetic chromatography. A table conveying the reported applications especially in the biomedical and environmental fields is given. On top of this, other on-line concentration methods for charged species, namely, s le self-stacking, acetonitrile stacking, sweeping, cation selective exhaustive injection-sweeping, and use of a pH junction, are briefly discussed.
Publisher: Wiley
Date: 2009
Abstract: Poor sensitivity is still considered to be one of the major limitations of electrophoresis, which is surprising given the power, flexibility and versatility of many of the approaches to on-line concentration that have developed over the last 20 years. This is still a very active area of interest and this review will cover developments in the field over the last two years since the last review (Electrophoresis 2007, 28, 254-281) through to June 2008. It includes developments in the fields of stacking, covering all methods from field- lified s le stacking and large volume s le stacking, through to ITP, dynamic pH junction and sweeping. Attention is also given to on-line or in-line extraction methods that have been used for electrophoresis.
Publisher: Wiley
Date: 16-06-2014
Abstract: CE can efficiently separate poly(3,4-ethylenedioxythiophene) oly(styrene sulfonic acid) (PEDOT/PSS) complexes and free PSS in dispersions and can be used to estimate the degree of PSS doping. We investigated the doping efficiency of PSS on PEDOT in dispersions using CE and its effect on the conductivity of the resulting PEDOT/PSS films. Results of this study indicate that dispersions containing 1:2.5-3 EDOT:PSS feed ratio (by weight) exhibiting 72-73% PSS doping generate highly processable and highly conductive films. Conductivity can be optimized by limiting the time of reaction to 12 h. At this point of the reaction, the PEDOT/PSS segments, appearing as broad band in the electropherogram, could still exist in an extended coil conformation favoring charge transport resulting in high conductivity. Above a threshold PEDOT length formed at reaction times longer than 12 h, the PEDOT/PSS complex, appearing as spikes in the electropherogram, most likely have undergone a conformational change to coiled core-shell structure restricting charge transport resulting in low conductivity. The optimal conductivity (5.2 S/cm) of films from dispersions synthesized for 12 h is significantly higher than those from its commercial equivalent Clevios P and other reported values obtained under similar conditions without the addition of codopants.
Publisher: Wiley
Date: 13-08-2014
Abstract: Although nonionic micellar electrokinetic chromatography is used for the separation of charged compounds that are not easily separated by capillary zone electrophoresis, the effect of the hydrophilic moiety of the nonionic surfactant has not been studied well. In this study, the separation of ultraviolet-absorbing amino acids was studied in electrokinetic chromatography using neutral polyoxyethylene lauryl ether surfactants (Adekatol) in the separation solution. The effect of the polyethylene moiety (the number of repeating units was from 6.5 to 50) of the hydrophobic test amino acids (methionine, tryptophan, and tysorine) was studied using a 10 cm effective length capillary. The separation mechanism was based on hydrophobic as well as hydrogen bonding interactions at the micellar surface, which was made of the polyoxyethylene moiety. The length of the polyoxyethylene moiety of the surfactants was not important in nonionic micellar electrokinetic chromatography mode.
Publisher: Elsevier BV
Date: 03-1998
Publisher: Springer Science and Business Media LLC
Date: 02-07-2016
DOI: 10.1007/S00216-016-9735-1
Abstract: Electrokinetic injection (EKI) in capillary zone electrophoresis (CZE) of charged analytes is by the electroosmotic flow (EOF) and electrophoretic mobility of analytes. In most forms of stacking with EKI, the s le ions were introduced via electrophoretic mobility and concentrated in a stacking boundary inside the capillary. In this work, we describe the unusual stacking of cationic analytes via EKI of sodium dodecyl sulfate (SDS) micelles into a fused silica capillary filled with acidic background solution (BGS) with 40-50 % acetonitrile. The analytes prepared with SDS micelles were injected because of their interaction with micelles or effective electrophoretic mobility. We observed two peaks from an analyte, and this suggested the concentration of analytes into two stacking zones. These two adjacent stacking zones were surprisingly maintained inside the capillary during EKI although the EOF was moving towards the inlet. The zones were identified as the SDS micelles (micelles zone) and organic solvent-rich stacking zone (solvent-rich zone) where the micelles zone was closer to the inlet end of capillary. The analytes concentrated in the solvent-rich zone through the mechanism of micelle to solvent stacking (MSS). The concentrated analytes in the micelles zone were from the concentrated analytes that electrophoretically migrated into the micelles zone from the solvent-rich zone during EKI. The analytes in the micelles zone were then re-stacked by MSS and formed the second sharp peak in CZE. This was prevented by reduction of acetonitrile concentration in the inlet BGS. A sensitivity enhancement factor of more than 100 was obtained for model cationic drugs (diphenhydramine and imipramine).
Publisher: Future Science Ltd
Date: 04-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4AN00557K
Abstract: Zero net-flow was observed when acrylamide based hydrogel was used in a vial at one end of a fused-silica capillary during electrophoresis with electroosmotic flow.
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.ACA.2018.08.009
Abstract: A core element in clinical diagnostics is the data interpretation obtained through the analysis of patient s les. To obtain relevant and reliable information, a methodological approach of s le preparation, separation, and detection is required. Traditionally, these steps are performed independently and stepwise. Microchip capillary electrophoresis (MCE) can provide rapid and high-resolution separation with the capability to integrate a streamlined and complete diagnostic workflow suitable for the point-of-care setting. Whilst standard clinical diagnostics methods normally require hours to days to retrieve specific patient data, MCE can reduce the time to minutes, hastening the delivery of treatment options for the patients. This review covers the advances in MCE for disease detection from 2008 to 2017. Miniaturised diagnostic approaches that required an electrophoretic separation step prior to the detection of the biological s les are reviewed. In the two main sections, the discussion is focused on the technical set-up used to suit MCE for disease detection and on the strategies that have been applied to study various diseases. Throughout these discussions MCE is compared to other techniques to create context of the potential and challenges of MCE. A comprehensive table categorised based on the studied disease using MCE is provided. We also comment on future challenges that remain to be addressed.
Publisher: Elsevier BV
Date: 08-2011
DOI: 10.1016/J.CHROMA.2011.06.071
Abstract: The performance of micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) was improved for anionic analytes using the long chain ionic liquid type cationic surfactant 1-dodecyl-3-methylimidazolium tetrafluoroborate (C₁₂-MIM-BF₄). The peak heights and corrected peak areas of the test profens and herbicides were enhanced up to 59 and 110-fold, respectively when compared to typical injection. These were up to 10 times better compared to the surfactant cetyltrimethyl ammonium bromide as MSS carrier. This performance was attributed to the properties of C₁₂-MIM-BF₄. MSS requires micelles in the s le for transport of bound analytes to a stacking boundary that contains an organic solvent for effective electrophoretic mobility reversal. The ionic liquid micelles provided better analyte transport properties that resulted from its hydrophobic and pi-pi interaction capabilities. The good solubility of the ionic liquid in high percentages of organic solvent also facilitated a more effective reversal of mobility. The LODs obtained for the test analytes were from 0.06 to 0.12 μg/mL. The linearity R² values in terms of peak height and corrected area were ≥ 0.99. The interday repeatabilities (%RSD, n=10,) were 0.5-2.2% for retention time, 1.9-4.7% for corrected areas and 4.1-6.4% for peak heights.
Publisher: American Chemical Society (ACS)
Date: 19-04-2010
DOI: 10.1021/AC902922U
Abstract: The utility of novel latex nanoparticles as pseudostationary phases for electrokinetic chromatography with UV and mass spectrometric detection is demonstrated. The nanoparticles are synthesized using ab initio RAFT (reversible addition-fragmentation chain transfer) in emulsion polymerization, which yields small (63 nm) particles with a narrow size distribution, a hydrophobic core, and an ionic shell. The nanoparticles are shown to provide efficient and selective separations, with retention and separation selectivity dominated by hydrophobic interactions. The nanoparticles are highly retentive, such that they are effective at relatively low concentrations. Addition of the nanoparticles to the background electrolyte at these concentrations has a minor effect on the noise with UV detection, no measurable effect on the separation current, and minor effects on analyte ionization efficiency during electrospray ionization. The nanoparticles do not cause fouling or degradation of the electrospray-mass spectrometer interface even after several weeks of use. The combination of online s le preconcentration via sweeping and selective mass spectrometric detection yields low detection limits (10-16 ppb), particularly for more hydrophobic compounds.
Publisher: Elsevier BV
Date: 10-2010
DOI: 10.1016/J.CHROMA.2010.07.077
Abstract: Micelle to solvent stacking (MSS) is a new on-line s le concentration technique for charged analytes in capillary zone electrophoresis (CZE). S le concentration in MSS mainly relies on the reversal in the effective electrophoretic mobility of the analyte at the boundary zone between the s le solution (S) and CZE background solution (BGS) inside the capillary. The basic condition for MSS is that the S is prepared in a matrix that contains an additive (i.e., micelles) which interacts with and has an opposite charge compared to the analytes. In addition, the BGS must contain a sufficient percentage of organic solvent. MSS was first reported for organic cations using anionic dodecyl sulfate micelles as additive in the S and methanol or acetonitrile as organic solvent in the BGS. Here, theoretical and experimental studies on MSS are described for organic anions using cationic cetyltrimethyl ammonium micelles as additive in the S and methanol as organic solvent in the BGS. Up to an order of magnitude improvement in concentration sensitivity was obtained for the test hypolipidaemic drugs using MSS in CZE with UV detection. The optimized method was also evaluated to the analysis of a spiked wastewater s le that was subjected to a simple extraction step.
Publisher: Wiley
Date: 04-2017
Abstract: A cationic cyclodextrin was used as dynamic coating for the capillary electrophoresis of a model mixture of proteins (i.e., ubiquitin, α-lactoglobulin, cytochrome-c, and myoglobin) as positively charged species in a fused silica capillary. An interesting feature of the coating is that by simple adjustment of the concentration of cyclodextrin added into the background electrolyte, a neutral or positively charged surface, which was beneficial in preventing protein adsorption at the inner capillary wall surface, was obtained. This is the first demonstration of a dynamic coating that yielded a neutral surface for protein separations in capillary electrophoresis. Based on electro-osmotic flow measurements, addition of 0.05 to 0.10 mg/mL quaternary β-cyclodextrin in a low pH electrolyte resulted in a neutral or positive surface (undetectable to very slow anodic electro-osmotic flow). The coating approach afforded the electrophoretic separation of the mixture of proteins at positive polarity with good repeatability and separation performance.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8GC00409A
Abstract: Open-tubular liquid chromatography with interfacial micelles.
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.CHROMA.2015.06.040
Abstract: Using a tee connector in a commercial capillary electrophoresis instrument, the effect of field lified s le injection from both flowing and static s le volumes was investigated. It is shown that under identical conditions (40min electrokinetic injection at 5kV from a s le volume of 295μL) the limit of detection using the continuous s le flow interface is 4 times lower than from a static vial. The relationship between different flow rates and injection voltages on the injected s le amount was also investigated using a 2D axisymmetric simulation (COMSOL 4.3b) and verified experimentally, confirming conditions under which there is near-quantitative injection of the s le target ions. Using electrokinetic injection at 30kV and a flow rate of 558nL/s the same enhancement from an even smaller volume of 184μL could be achieved in 5.5min than could be achieved from 295μL and a 40min injection. This sensitivity enhancement factor corresponded to four orders of magnitude improvement compared to a hydrodynamic injection. This is the first report showing that a continuous s le flow interface combined with stacking methods under conditions approaching quantitative injection from the entire s le volume has the potential to be more sensitive than a static system.
Publisher: Elsevier BV
Date: 03-2008
DOI: 10.1016/J.CHROMA.2007.11.001
Abstract: On-line preconcentration is one of the aspects of analytical method development using capillary electrophoretic techniques. The choice of the s le matrix alone can significantly alter both method sensitivity and separation efficiency. The recent trend to detect s les in narrower separation vessels also necessitates the need to improve detection sensitivity. The desire to detect very low levels of analytes using limited amounts of s le from biological specimens and the high separation efficiency obtainable using very large injections compared to classical small size injections also adds to this list. Indeed, one of the rich areas of research in the capillary electrophoresis field is on on-line s le preconcentration. More than 400 published research articles gathered from the www.webofscience.com from the year 2000 described a form of on-line preconcentration in capillary electrophoresis. This review provides a comprehensive table listing the applications of on-line preconcentration in capillary electrophoresis.
Publisher: MDPI AG
Date: 12-09-2021
DOI: 10.3390/MOLECULES26185531
Abstract: Bile salts are naturally occurring chiral surfactants that are able to solubilize hydrophobic compounds. Because of this ability, bile salts were exploited as chiral selectors added to the background solution (BGS) in the chiral micellar electrokinetic chromatography (MEKC) of various small molecules. In this review, we aimed to examine the developments in research on chiral MEKC using bile salts as chiral selectors over the past 20 years. The review begins with a discussion of the aggregation of bile salts in chiral recognition and separation, followed by the use of single bile salts and bile salts with other chiral selectors (i.e., cyclodextrins, proteins and single-stranded DNA aptamers). Advanced techniques such as partial-filling MEKC, stacking and single-drop microextraction were considered. Potential applications to real s les, including enantiomeric impurity analysis, were also discussed.
Publisher: Wiley
Date: 28-07-2011
Abstract: Ethylenediaminetetraacetic acid (EDTA) in the background electrolyte (BGE) of capillary zone electrophoresis coupled to an electrospray ionization mass spectrometer is presented as an approach for the determination of metal ions. Significant signals for the metal-ligand complexes were observed even when EDTA was continually eluted from the capillary during the entire electrophoretic run. The signal-to-noise ratio was improved by the addition of ammonia to the sheath liquid and by using an acquisition m/z range above the m/z of EDTA. The LODs for the test metal ions (i.e. calcium(II), manganese(II), and zinc(II)) with conventional injection were around 1-2 mg/L with corrected peak areas that are linear from 8 to 100 mg/L. The presence of EDTA in the BGE was critical not only for the separation but also for sweeping via complexation as an on-line s le concentration technique. The peak height of the test metal ions was improved at least tenfold with sweeping via EDTA complexation and yielded LODs in the μg/L range.
Publisher: Wiley
Date: 05-11-2012
Abstract: A transient micellar phase extractor using CTAB was described for the online s le concentration of various anionic analytes (drugs and herbicides) in CE. Stacking and separation was performed at neutral pH in coelectroosmotic flow in a hexadimethrine bromide coated fused-silica capillary. A micellar plug (e.g. 10 mM CTAB) was injected prior to hydrodynamic injection of the analytes prepared in aqueous organic solvent (e.g. with 30% ACN). In the presence of an electric field, the micelles interacted with the anions inside the capillary. This was followed by selective analyte focusing via the mechanism of micelle to solvent stacking. The micelles acted as transient extractor because the stacking ends when the injected micelles completely migrated through the boundary between the s le and micellar plug. Fundamental studies were performed (effect of surfactant concentration, etc.) and the technique yielded 13- to 30-fold improvements in peak height. A stacking CE method in conjunction with liquid-liquid extraction was also tested for the detection of the herbicides fenoprop and mecoprop in fortified drinking water at analyte concentration levels relevant to Australian Drinking Water Guidelines.
Publisher: Elsevier BV
Date: 08-1998
DOI: 10.1016/S0378-4347(98)00063-2
Abstract: Utility of a second enhanced field zone (water zone) is investigated for the on-line concentration of neutral analytes in micellar electrokinetic chromatography. Micellar solutions of sodium dodecyl sulfate prepared in acidic phosphate buffers are used as separation and s le solutions. Prior to long hydrodynamic injection of s les prepared in a low conductivity matrix, a long water plug is hydrodynamically injected to provide a second enhanced field zone. Practical and some fundamental considerations are presented. The technique is selective towards hydrophobic analytes. Notable detector response improvements (>100-fold) for several analytes are observed experimentally.
Publisher: Elsevier BV
Date: 08-1999
DOI: 10.1016/S0021-9673(99)00504-X
Abstract: An application study of an on-line concentration technique of neutral analytes for micellar electrokinetic chromatography (MEKC) was carried out in environmental analysis to enhance the UV detection sensitivity. Several dioxins and related compounds, such as dibenzofuran, dibenzo-p-dioxin, 2,3- and 2,7-dichlorodibenzo-p-dioxins, and 2,3,7-trichlorodibenzo-p-dioxin, were used as test solutes. For a highly sensitive separation and detection, cyclodextrin-modified MEKC (CD-MEKC) under acidic conditions was employed as a separation mode and stacking using reverse migrating micelles and a water plug (SRW) as an on-line concentration technique. Almost a 200-fold gain in detection sensitivity was obtained for the model compounds in SRW-CD-MEKC compared to that in normal CD-MEKC without on-line concentration and the limit of detection was found to be around 0.1 ppm for each solute.
Publisher: Wiley
Date: 15-03-2016
Abstract: Micelle to solvent stacking was implemented for the recently established NACE-C(4) D method to determine tamoxifen and its metabolites in standard s les and human plasma of breast cancer patients. For stacking, the standard s les and extract after liquid-liquid extraction (LLE) were prepared in methanol and the resulting s le solution was pressure injected after a micellar plug of SDS. Factors that affected the stacking such as SDS concentration, micelle, and s le plug length were examined. The sensitivity enhancement factor (peak height from stacking eak height from typical injection of s le in BGE) was 15-22. The method detection limits with LLE were in the range of 5-10 ng/mL, which was lower than the established method (where the LLE extract was also prepared in methanol) with reported method detection limits of 25-40 ng/mL. The intraday and interday repeatability were in the range of 1.0-3.4% and 3.8-6.5%, respectively.
Publisher: Elsevier BV
Date: 12-2019
DOI: 10.1016/J.ACA.2019.08.016
Abstract: This review critically discusses the developments on open-tubular liquid chromatography (OT-LC) and open-tubular capillary electrochromatography (OT-CEC) during 2014-2018. An appropriate Scopus search revealed 5 reviews, 4 theoretical papers on open-tubular format chromatography, 29 OT-LC articles, 68 OT-CEC articles and 4 OT-LC/OT-CEC articles, indicating a sustained interest in these areas. The open-tubular format typically uses a capillary column with inner walls that are coated with an le layer or coating of solid stationary phase material. The ratio between the capillary internal diameter and coating thickness (CID/CT) is ideally ≤ 100 for appropriate chromatographic retention. We, therefore, approximated the CID/CT ratios and found that 22 OT-LC papers have CID/CT ratios ≤100. The other 7 OT-LC papers have CID/CT ratio >100 but have clearly demonstrated chromatographic retention. These 29 papers utilised reversed phase or ion exchange mechanisms using known or innovative solid stationary phase materials (e.g. metal organic frameworks), stationary pseudophases from ionic surfactants or porous supports. On the other hand, we found that 68 OT-CEC papers, 7 OT-LC papers and 4 OT-LC & OT-CEC papers have CID/CT ratios >100. Notably, 44 papers (42 OT-CEC and 2 OT-LC & OT-CEC) did not report the retention factor and/or effective electrophoretic mobility of analytes. Considering all covered papers, the most popular activity was on the development of new chromatographic materials as coatings. However, we encourage OT-CEC researchers to not only characterise changes in the electroosmotic flow but also verify the interaction of the analytes with the coating. In addition, the articles reported were largely driven by stationary phase or support development and not by practical applications.
Publisher: Elsevier BV
Date: 08-2002
DOI: 10.1016/S0021-9673(01)01499-6
Abstract: Sweeping in capillary electrophoresis (CE) involves the interaction of a pseudostationary phase (PS) in the separation solution and a s le in the matrix that is free of the PS used. The PS includes not only the PSs employed in electrokinetic chromatography, but also complexation reagents such as borate. The s le matrix could have a lower, similar, or higher conductance than the separation solution. Thus, the basic condition for sweeping is a s le matrix free of the additive. The accumulation of analyte molecules during the interaction makes this interesting phenomenon very useful as an on-line preconcentration method for CE. Preconcentration occurs due to chromatographic partitioning, complexation, or any interaction between analytes and PS. Contact between analyte and PS is facilitated by the action of electrophoresis and is independent of electroosmosis. The analyte, PS, or both should have electrophoretic velocities when an electric field is applied. The extent of preconcentration is dictated by the strength of the interaction involved. From tens to several thousand-fold improvements in detector response for many neutral and charged analytes have been achieved with this technique, suggesting sweeping as a general approach to on-line preconcentration in CE. The mechanism and applications of the sweeping phenomenon under different experimental conditions are discussed in this review, with particular emphasis on a better understanding of the sweeping mechanism under reduced electric field (high conductivity) in the s le zone.
Publisher: Wiley
Date: 22-11-2013
Abstract: Analytical methods for chiral compounds require a separation step prior to mass spectrometric detection. CE can separate enantiomers by the use of a chiral selector and can be hyphenated with MS. The chiral selector can be either embedded inside the capillary (electrochromatography) or added into the background solution (EKC). This review describes the fundamentals and highlights the recent developments (September 2009-May 2013) of chiral CEC and EKC with detection using MS. There were 20 research and more than 30 review papers during this period. The research efforts were driven by fundamental studies, such as the development of novel chiral selectors in electrochromatography and of advanced partial filling techniques in EKC in order to optimise separation. Other developments were in application studies, such as in food analytics and metabolomics.
Publisher: MDPI AG
Date: 28-05-2021
Abstract: Alkenylbenzenes are potentially toxic (genotoxic and carcinogenic) compounds present in plants such as basil, tarragon, anise star and lemongrass. These plants are found in various edible consumer products, e.g., popularly used to flavour food. Thus, there are concerns about the possible health consequences upon increased exposure to alkenylbenzenes especially due to food intake. It is therefore important to constantly monitor the amounts of alkenylbenzenes in our food chain. A major challenge in the determination of alkenylbenzenes in foods is the complexity of the s le matrices and the typically low amounts of alkenylbenzenes present. This review will therefore discuss the background and importance of analytical separation methods from papers reported from 2010 to 2020 for the determination of alkenylbenzenes in foods and related products. The separation techniques commonly used were gas and liquid chromatography (LC). The s le preparation techniques used in conjunction with the separation techniques were various variants of extraction (solvent extraction, liquid-liquid extraction, liquid-phase microextraction, solid phase extraction) and distillation (steam and hydro-). Detection was by flame ionisation and mass spectrometry (MS) in gas chromatography (GC) while in liquid chromatography was mainly by spectrophotometry.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5AY02493E
Abstract: In the last decade, capillary electrophoresis (CE) has joined other analytical separation techniques that are widely used in metabolomics.
Publisher: Elsevier BV
Date: 07-2015
DOI: 10.1016/J.CHROMA.2015.05.018
Abstract: S le preparation by electrophoretic concentration, followed by analysis using sweeping-micellar electrokinetic chromatography, was studied as a green and simple analytical strategy for the trace analysis of cationic drugs in water s les. Electrophoretic concentration was conducted using 50 mmol/L ammonium acetate at pH 5 as acceptor electrolyte. Electrophoretic concentration was performed at 1.0 kV for 50 min and 0.5 kV and 15 min for purified and 10-fold diluted waste water s les, respectively. Sweeping-micellar electrokinetic chromatography was with 100 mmol/L sodium phosphate at pH 2, 100 mmol/L sodium dodecyl sulfate and 27.5%-v/v acetonitrile as separation electrolyte. The separation voltage was -20 kV, UV-detection was at 200 nm, and the acidified concentrate was injected for 36 s at 1 bar (or 72% of the total capillary length, 60 cm). Both purified water and 10-fold diluted waste water exhibited a linear range of two orders of concentration magnitude. The coefficient of determination, and intra- and interday repeatability were 0.991-0.997, 2.5-6.2, and 4.4-9.7%RSD (n=6), respectively, for purified water. The values were 0.991-0.997, 3.4-7.1, and 8.7-9.8%RSD (n=6), correspondingly, for 10-fold diluted waste water. The method detection limit was in the range from 0.04-0.09 to 1.20-6.97 ng/mL for purified and undiluted waste water, respectively.
Publisher: Wiley
Date: 25-03-2011
Abstract: Online s le concentration of acidic drugs by transient isotachophoresis (t-ITP) with the injection of a base is described in capillary zone electrophoresis (CZE). A positively coated capillary was conditioned with background electrolyte (ammonium acetate at pH 6). A long plug of s le solution (S) prepared in ammonium acetate was then hydrodynamically injected followed by the base (tetrapropylammonium hydroxide). A negative voltage was applied and caused the hydroxide ions from the base to penetrate the S zone and created a pH junction that swept through the S zone. The analytes stack at the junction where the mechanism of focusing was transient ITP with the acetate and hydroxide ions as leading and terminating ions, respectively. The concentrated analytes separated in co-EOF CZE once the hydroxide was exhausted. The base stacking strategy was tested using hypolipidemic, nonsteroidal anti-inflammatory, and diuretic drugs, and afforded 19-37 improvements in peak height.
Publisher: American Chemical Society (ACS)
Date: 09-10-2001
DOI: 10.1021/AC015522R
Abstract: In chromatographic separations, the heights of peaks are proportional to the concentrations of s le components present in an injected mixture. In general, an increase in the peak height cannot be achieved by simply increasing the injection time or the s le plug length. An exception occurs if some form of on-line preconcentration is possible. We present a new strategy for achieving on-line preconcentration by the use of a porous chromatographic material that acts as a solid-phase extractor as well as a stationary-phase separator. We are able to realize significant on-line preconcentration using capillary columns filled with a photopolymerized sol-gel (PSG). More than 2-cm plugs of s le solution can be loaded into the capillary and concentrated using a running buffer that is the same as the injection buffer (to avoid solvent gradient effects). As a demonstration, mixtures of three different polycyclic aromatic hydrocarbons, eight different alkyl phenyl ketones, and five different peptides in solutions of aqueous acetonitrile have been injected onto the PSG column and separated by capillary electrochromatography. The preconcentration is marked in terms of peak heights, with up to 100-fold increase for the PAH mixture, 30-fold for the alkyl phenyl ketone mixture, and 20-fold for the peptide mixture. Preconcentration takes place because of the high mass-transfer rates possible in the highly porous structure, and the extent of preconcentration follows the retention factor k for a given analyte.
Publisher: Springer Science and Business Media LLC
Date: 21-07-2010
Publisher: Wiley
Date: 29-04-2020
Abstract: Capillary electrophoresis has been alive for over two decades now yet, its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with an update published in 2009 and covers material published through to June 2010. It includes developments in the fields of stacking, covering all methods from field- lified s le stacking and large volume s le stacking, through to ITP, dynamic pH junction and sweeping. Attention is also given to on-line or in-line extraction methods that have been used for electrophoresis.
Publisher: American Chemical Society (ACS)
Date: 24-12-2019
DOI: 10.1021/ACS.ANALCHEM.8B03542
Abstract: Analyte focusing by micelle to cyclodextrin stacking (MCDS) in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) and fused silica capillaries is demonstrated for neutral, cationic, and chiral analytes. The stacking was at a dynamic boundary formed between the injected charged SDS micelles and neutral γ-cyclodextrin (γ-CD) zones, where the analytes bound inside micelles were released due to the formation of stable SDS-CD inclusion complexes. The complex formation reduced or eliminated the affinity of the analytes to the micellar phase. There was reversal (for charged) or nulling (for neutrals) of the analyte's effective electrophoretic mobility that caused the analytes to accumulate at the boundary. Under the conditions where the SDS micelles velocity is faster than the electroosmotic flow (using acidic buffer), MCDS was conducted by injection of a long plug of s le in a micellar diluent after injection of a CD solution plug into a capillary that was filled with MEKC background solution. By simply extending the length of the CD plug, chiral separations of chlorpheniramine and phenoxyacid herbicides were achieved without optimizing the MEKC conditions. The analytical figures of merit including linearity and repeatability for the tested compounds were found acceptable, and the sensitivity enhancement factors were up to 171. The stacking strategy in MEKC was applied to metabolic stability studies of small molecules with HepG2 cell line, where the s les were only treated with acetonitrile and then diluted with the micellar diluent (demonstrating the reduction of tedious s le preparation requirements for biological s les prior to chemical analysis).
Publisher: American Chemical Society (ACS)
Date: 10-04-2015
DOI: 10.1021/AC504765H
Abstract: A s le preparation device for the simultaneous enrichment and separation of cationic and anionic analytes was designed and implemented in an eight-channel configuration. The device is based on the use of an electric field to transfer the analytes from a large volume of s le into small volumes of electrolyte that was suspended into two glass micropipettes using a conductive hydrogel. This simple, economical, fast, and green (no organic solvent required) s le preparation scheme was evaluated using cationic and anionic herbicides as test analytes in water. The analytical figures of merit and ecological aspects were evaluated against the state-of-the-art s le preparation, solid-phase extraction. A drastic reduction in both s le preparation time (94% faster) and resources (99% less consumables used) was observed. Finally, the technique in combination with high-performance liquid chromatography and capillary electrophoresis was applied to analysis of quaternary ammonium and phenoxypropionic acid herbicides in fortified river water as well as drinking water (at levels relevant to Australian guidelines). The presented sustainable s le preparation approach could easily be applied to other charged analytes or adopted by other laboratories.
Publisher: Wiley
Date: 03-03-2016
Abstract: The synergistic stacking approach of field-enhanced s le injection-micelle-to-solvent stacking was used for high sensitivity CZE-ESI-MS of eight penicillins and sulfonamides. Sensitivity enhancement factors (peak height) were 1629-3328 compared to typical injection, with LODs from 0.11 to 0.55 ng/mL. The analytical figures of merit were acceptable. SPE on a fortified seawater s le resulted in 50-fold enrichment with recoveries of 85-110%. The overall method LODs were 0.002-0.011 ng/mL.
Publisher: American Chemical Society (ACS)
Date: 26-05-2011
DOI: 10.1021/AC200684T
Abstract: A repeatable preconcentration electrophoretic methodology for the analysis of bacteria was developed. This method is based on an isotachophoretic mode coupled with a simultaneous hydrodynamic-electrokinetic injection in conditions of field- lified s le injection. This electrophoretic method allows the quantification of Enterobacter cloacae (studied as a model of Gram negative bacteria) with a limit of detection of 2 × 10(4) cells/mL. With the optimized conditions, a preconcentration factor of about 500-fold was obtained as compared to a standard hydrodynamic injection. The RSD (n = 5) on the migration time and on the peak area were 3% and 5%, respectively. This capillary electrophoretic methodology has been applied for the quantification of microbes in natural water (river and natural spring waters). Filtration of the s le prior to injection was required to remove ions present in the water and to keep the field- lified s le injection condition at the injection. Filtrated bacteria were then recovered in terminating electrolyte diluted 10 times with water. Good agreements were obtained between cellular ATP measurements and the proposed CE methodology for the quantification of bacteria in waters.
Publisher: Wiley
Date: 05-2013
Abstract: Sweeping, an on-line s le concentration technique in CE, is the picking and accumulation of analytes by the pseudostationary phase or complexing additive. In the presence of an electric field, the analytes concentrated at the additive front that initially penetrated the s le zone. Here, we describe the sweeping of cationic alprenolol enantiomers using sulfated β-CD and organic solvent. The separation solution contained the anionic additive while ACN was in the s le solution. With fused silica capillaries, positive polarity, and solutions buffered at pH 3, the direction of the enantiomers' effective electrophoretic mobility was the same as the electrophoretic mobility (or electrophoretic mobility without additive). When the amount of ACN in the s le was increased (i.e. 60%), the interaction between the analytes and additive became negligible. This caused the sweeping boundary to shift from the electrophoretically moving β-CD front to the zone between the s le and separation solution. The equation that described the narrowing of injected s le zone was derived. The performance of sweeping with 60% ACN in the s le was then studied under different operating conditions (e.g. type of injection, injection time, and CD concentration). The low interaction between enantiomers and additive gave only moderate increases in sensitivity (approximately tenfold), but was improved when field enhancement was used during electrokinetic injection. With a conductivity difference (separation/s le solution) of 70 and a short injection time of 30 s at 20 kV, peak improvements of >100-fold was easily achieved.
Publisher: Elsevier BV
Date: 11-2010
DOI: 10.1016/J.CHROMA.2010.09.069
Abstract: The preparation of processable graphene oxide colloids called chemically converted graphene (CCG) involves the following steps: oxidation of graphite to form graphite oxide exfoliation of graphite oxide to form graphene oxide (GO) and reduction of GO to form CCG. In this work, the exfoliation and reduction steps were monitored by capillary zone electrophoresis (CZE). CZE was performed in fused silica capillaries with UV absorbance at 230 nm (GO) and 270 nm (CCG) using 250 μM tetrapropylammonium hydroxide (pH 10.4). The results indicate that almost complete exfoliation of graphite oxide (0.05 wt%) and higher recovery of CCG were obtained by sonication at 50% power for more than 15 h. CZE is considered a valuable tool for the fractionation and analysis of GO nanoparticles and, hence, for the control of different steps in preparation of CCG.
Publisher: Wiley
Date: 04-07-2016
Publisher: Elsevier BV
Date: 04-1999
Publisher: Elsevier BV
Date: 07-2014
DOI: 10.1016/J.CHROMA.2014.05.050
Abstract: S le clean-up by cloud point phase separation and analysis by capillary electrophoresis with stacking was developed for quaternary ammonium herbicides (i.e., paraquat and diquat) in milk. For s le clean-up, a mixture of 845μL of milk s le, 5μL of 100mM phosphoric acid, and 150μL of Triton X-114 was heated (60°C for 2min) and centrifugated (3000rpm for 2min) in 2-mL Eppendorf tube. The upper phase was directly analysed by capillary electrophoresis via electrokinetic injection at 10kV for 150s. The separation electrolyte was 100mM phosphate buffer with 20% acetonitrile at pH 2.5. Before s le injection, a micellar solution (10mM SDS in 80mM phosphate buffer at pH 2.5) and an organic solvent rich solution (30% ACN) was hydrodynamically introduced into the capillary. These solutions provided the necessary conditions for stacking the cationic herbicides via the combination of field enhanced s le injection and micelle to solvent stacking. The LODs (S/N=3) obtained from the entire strategy for paraquat and diquat in milk was 0.004 and 0.018μg/mL, respectively. This is 1.5 to >2 orders of magnitude better than the corresponding LODs obtained from the electrophoretic analysis of herbicide standards prepared in the separation electrolyte. The strategy was also successfully applied to 5 milk s les available in the market.
Publisher: Wiley
Date: 12-11-2013
DOI: 10.1002/CHIR.22257
Abstract: The concentration sensitivity of a racemic drug (chlorpheniramine maleate) in chiral capillary electrophoresis with electrospray ionization – mass spectrometric detection was improved ~500-fold via stacking. Enantiomeric separation was achieved through the use of a neutral chiral pseudostationary phase (2-hydroxpropyl-β-cyclodextrin), untreated fused-silica capillaries, and the application of a partial-filling technique to prevent the pseudostationary phase from entering the detector. A concentration factor of 50 resulted from field-enhanced s le injection(FESI). However, the higher concentration factor was achieved by combining FESI with micelle-to-solvent stacking (MSS) to increase s le load and focus the analyte band. MSS was achieved by injection of an ammonium lauryl sulfate micellar plug prior to s le injection. The s le diluent was a 20-fold dilution of the background electrolyte (50 mM ammonium acetate, pH 3.5) with 60% acetonitrile. This methodology provided a limit of detection (LOD) of as low as 5 ng/ml of the racemate.
Publisher: Wiley
Date: 07-12-2011
Abstract: An extensive search of the published research and review articles indicated a growing number of works that employed electroseparation techniques. Capillary zone electrophoresis (CZE) and electrokinetic chromatography (EKC), in particular, were found to be popular for the analyses of natural products. This review outlines the important developments in this field over the years, especially during the 2006-2010 period. An overview of the natural product applications such as pharmaceuticals/herbal products, fingerprinting and quality control, food and food contaminants, and toxicological compounds of interest to forensics were presented. Important areas of detection strategies, microchips, s le preconcentration, and chiral separations were also discussed. Hence, quick information was provided on the researches already undertaken and the possibilities of unexplored areas. In addition, fundamental concepts for the understanding of CZE and EKC and their suitability for natural products analyses were briefly discussed.
Publisher: Elsevier BV
Date: 12-2012
DOI: 10.1016/J.CHROMA.2012.09.100
Abstract: The application of capillary electrophoresis (CE) with on-line photodiode array detection to the analysis of processable poly(3,4-ethylenedioxythiophene) olystyrene sulfonate (PEDOT/PSS) aqueous dispersions is presented. The dispersions were prepared by oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of PSS. The separation of PEDOT/PSS complexes and PSS was achieved using sodium borate (pH 9.2) in a fused silica capillary and positive polarity. The electrophoretic behavior and UV spectra of the negatively charged complexes were correlated to the amount of PEDOT attached to PSS. The ability of CE to predict the conductivity of films produced from spin coating of PEDOT/PSS dispersions was also proposed.
Publisher: Elsevier BV
Date: 07-2013
DOI: 10.1016/J.CHROMA.2013.05.055
Abstract: Cationic or anionic molecules can be selectively injected from an aqueous mixture of charged and neutral species into a capillary by electrophoresis. Under stacking conditions, this selective field enhanced s le injection was studied here as a potential s le preparation technique for the clean-up or purification of microliter s les. As a simple demonstration, cationic small molecules were removed or extracted from a 100μL s le mixture using a commercial capillary electrophoresis instrument. The extraction was monitored using an on-line UV detector. Results from the micellar electrokinetic chromatography analysis of treated and untreated s le revealed significant reduction of cationic species in the treated s le. The technique is essentially a sequence of field enhanced s le injection experiments in capillary electrophoresis.
Publisher: American Chemical Society (ACS)
Date: 03-08-2018
DOI: 10.1021/ACS.ANALCHEM.8B01707
Abstract: The removal of sodium dodecyl sulfate (SDS) in SDS-assisted proteomics with electrospray-ionization-mass-spectrometric (ESI-MS) analysis is an essential step in the analysis. Off-line state-of-the-art s le-preparation strategies can allow 100% removal of DS
Publisher: Wiley
Date: 22-01-2022
Abstract: The chiral separation of various analytes (dichlorprop, mecoprop, ibuprofen, and ketoprofen) was demonstrated with different cyclodextrins as mobile phase additives in open‐tubular liquid chromatography using a stationary pseudophase semipermanent coating. The stable coating was prepared by a successive multiple ionic layer approach using poly(diallyldimethylammonium chloride), polystyrene sulfonate, and didodecyldimethyl ammonium bromide. Increasing concentrations (0–0.2 mM) of various native and derivatized cyclodextrins in 25 mM sodium tetraborate (pH 9.2) were investigated. Chiral separation was achieved for the four test analytes using 0.05–0.1 mM β‐cyclodextrin (resolution between 1.11 and 1.34), γ‐cyclodextrin (resolution between 0.78 and 1.27), carboxymethyl‐β‐cyclodextrin (resolution between 1.64 and 2.59), and 2‐hydroxypropyl‐β‐cyclodextrin (resolution between 0.71 and 1.76) with the highest resolutions obtained with 0.1 mM carboxymethyl‐β‐cyclodextrin. %RSD values were %. This is the first demonstration of chiral open‐tubular liquid chromatography using achiral chromatographic coatings and cyclodextrins as mobile phase additives.
Publisher: American Chemical Society (ACS)
Date: 17-03-2000
DOI: 10.1021/AC990566+
Abstract: The concept of sweeping neutral analytes using a high-conductivity matrix or under a reduced electric field in micellar electrokinetic chromatography (MEKC) using anionic micelles and in the presence of electroosmotic flow is presented. Three important processes are identified. First, stacking of the micelles at the cathodic interface between the s le solution (S) and background solution (BGS) zones is identified. This is then followed by the sweeping of analyte molecules by the stacked micelles that enter the S zone. Finally, the destacking of the stacked micelles at the anodic interface between the S and BGS zones occurs. The stacking of the micelles improves the focusing effect of sweeping by a factor approximately equal to the ratio of conductivities between the S and BGS zones (ratio = enhancement factor = gamma'). However, the destacking of the stacked micelles broadens the swept zones by a factor approximately equal to 1/gamma'. In effect, the focusing effect of sweeping using a matrix with equal or higher conductivity compared to the BGS will be roughly the same. The micelle stacking and destacking mechanisms are verified experimentally. This paper also provides comments on the mechanism of neutral analyte focusing under similar conditions proposed by another group.
Publisher: Elsevier BV
Date: 09-1997
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.CHROMA.2015.10.089
Abstract: The sensitivity enhancement factor (SEF) in field enhanced s le injection (FESI) in capillary electrophoresis is dictated by the conductivity ratio. The higher the conductivity ratio (using very low conductivity s le diluents such as water), the higher the SEF. Here, we improved the performance of FESI by combination with sweeping and micelle to solvent stacking (MSS) in a well-defined three-step stacking procedure using model cationic drugs. The separation was by capillary zone electrophoresis (CZE) using 100mM phosphoric acid as background solution (BGS). Under the experimental conditions studied, the SEF (vs. typical injection in CZE) range of FESI using a conductivity ratio of 10, 100, and 1000 (s le diluent with conductivity 10, 100, and 1000× lower than the BGS, respectively) was 5-6, 33-50, and 272-393, respectively. The SEF range of three-step stacking was 308-891, 2188-6463, and 3088-6499, correspondingly. The SEF enhancement factor due to three-step stacking (SEF of three-step stacking ided by SEF of FESI) was from 11 to 161. We evaluated the performance of proposed procedure using a conductivity ratio of 10 (10mM phosphoric acid as diluent) which is the minimum requirement for field-enhancement. The strategy was as follows: long FESI (e.g., 420s at 10kV) to form an overloaded stacked zone sweeping (e.g., 315s at -10kV) with 10mM sodium dodecyl sulfate micelles and MSS by injection (6s at 50mbar) of 30% acetonitrile. The strategy was studied in terms of sweeping and MSS conditions, FESI/sweeping time ratio, and FESI time at constant FESI/sweeping ratio. Analytical figures of merit including linearity, LOD (S/N=3), and repeatability (intraday and interday) were determined. Moreover, s le matrix effect was studied using acetone treated plasma s le.
Publisher: American Chemical Society (ACS)
Date: 27-02-2014
DOI: 10.1021/AC500090N
Abstract: Interface-free two-dimensional heart-cutting capillary electrophoresis is typically used to purify/concentrate and separate a single target fraction. Here, we demonstrate the simultaneous stacking and orthogonal separation of target fractions that belong to two different classes of compounds. The cationic species were first analyzed by capillary zone electrophoresis using an electrolyte of low pH in a fused-silica capillary. The neutrals that remained inside the capillary after the first dimension analysis were then separated by micellar electrokinetic chromatography using sodium dodecyl sulfate micelles that were electrophoretically introduced into the capillary. The suppression of electro-osmotic flow using low pH was essential in shifting the separation selectivity from electrophoresis to electrokinetic chromatography. Two approaches to stacking based on the solubility of the species present were developed. Stacking was achieved during the first dimension analysis via sweeping and/or analyte focusing by micelle collapse. Two artificial mixtures (eight cationic drugs/five neutral steroids, and three quaternary ammonium/three neutral organophosphate pesticides) were successfully analyzed with sensitivity enhancement factors from 15 to 100. Some analytical parameters and application to a spiked real water s le were also studied.
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.CHROMA.2014.10.006
Abstract: An off-line electrophoretic s le concentration technique for charged analytes in aqueous s les is presented. As a demonstration, nine anions including inorganic ions, a dye and benzenesulfonate derivatives were enriched from a 10 mL s le solution into 20 μL electrolyte inside a glass micropipette. A hydrogel was placed at one end of the micropipette while the other end was immersed in the s le. The electric field caused the movement and concentration of anions into the high conductivity electrolyte. The technique was applied to purified, drinking and river water and was optimised by changing applied voltage and voltage application time. The LODs after analysis by capillary electrophoresis was 1-19 ng/mL, 4-133 ng/mL and 18-80 ng/mL for purified, drinking and river water, respectively. The linear range was 0.002-0.048 to 0.1-2.4 μg/mL (R(2) of 0.993-0.999), 0.02-0.24 to 1.0-24 μg/mL (R(2) of 0.995-0.999) and 0.02-0.24 to 1.0-24 μg/mL (R(2) of 0.998-1.000), correspondingly. The intraday and interday repeatability (%RSD, n=6) was ≤7.4% and 14.0%, respectively. The concentration factor was from one to two orders of magnitude. The technique was directly compatible with a liquid phase analytical technique, thus eliminated the additional steps (e.g., evaporation, elution and/or reconstitution) which are typically performed in s le preparation (e.g., liquid and solid phase extraction).
Publisher: Wiley
Date: 07-2015
Abstract: Interface-free two-dimensional heart-cutting capillary electrophoresis for two different classes of analytes (anionic and neutral) in a single capillary is presented. Simultaneous s le stacking and orthogonal separation were demonstrated. The anionic species were first analyzed by capillary zone electrophoresis in the first dimension. Then, the neutral compounds were separated in the second dimension by micellar electrokinetic chromatography using the common anionic surfactant sodium dodecyl sulfate. The first and second dimensions occurred automatically without changing the electrolyte and without polarity switching. Artificial mixtures (five anions and four neutral compounds) were successfully analyzed with sensitivity enhancement factors from 7 to 28. The orthogonal separation was complete within 8 min. Some analytical features and application to a spiked real river water s le were also studied.
Publisher: American Chemical Society (ACS)
Date: 10-07-2001
DOI: 10.1021/AC0100749
Abstract: A solution of methacryloxypropyltrimethoxysilane in the presence of an acid catalyst, water, toluene, and a photoinitiator was irradiated at 365 nm for 5 min in a 75-microm i.d. capillary to prepare a porous monolithic sol-gel column by a one-step, in situ, process. The photopolymerized sol-gel (PSG) column shows reversed-phase behavior. Using this column, a variety of low-molecular-weight neutral compounds, including polycyclic aromatic hydrocarbons, alkyl benzenes, alkyl phenyl ketones, and steroids are separated from mixtures. Various different operational parameters, such as buffer composition, field strength, and column temperature, were varied to assess their influence on column performance. Use of PSG as a stationary phase for a pressure-driven separation is also demonstrated.
Publisher: Elsevier BV
Date: 2014
Publisher: Wiley
Date: 30-03-2016
Abstract: In this communication, we present a very simple strategy to focus covalently derivatized proteins for high sensitivity CE analysis by LIF detection. We demonstrated that the covalently tagged protein can be focused just by adding SDS at a concentration above the CMC in the derivatized s le. Under specific injection conditions, SDS concentration below the CMC is also sufficient to induce the focusing of the tagged protein. This method allows the quantification and detection of the covalently tagged protein in a narrow zone with an efficiency approaching 220 000 plates/m. Very good linearity was obtained for the ubiquitin in a concentration range of 2-25 μM.
Publisher: Elsevier BV
Date: 07-1999
DOI: 10.1016/S0021-9673(99)00204-6
Abstract: On-line s le concentration of fast moving inorganic anions by large volume s le stacking (LVSS) and field enhanced s le injection (FESI) with a water plug under acidic conditions is presented. Detection sensitivity enhancements were around 100 and 1000-fold for LVSS and FESI, respectively. However, reproducibility and linearity of response in the LVSS approach is superior compared to the FESI approach.
Publisher: Elsevier BV
Date: 07-2012
DOI: 10.1016/J.ACA.2012.04.032
Abstract: Simultaneous electrokinetic and hydrodynamic injection (SEHI) of organic cations (tricyclic antidepressant and beta blocker drugs) with on-line s le concentration using micelle to solvent stacking (MSS) was studied in micellar electrokinetic chromatography. Compared to conventional injection, >300-fold improvements in signals were obtained by hydrodynamic injection. However, with SEHI the amount of s le ions introduced into the capillary was increased which afforded a higher gain of up to 4000-fold without compromise to separation efficiency. The electrokinetic injection at negative polarity (anode at the detector end) introduced the micelle bound analytes. The hydrodynamic injection also maintained the MSS boundary inside the capillary. The stability of the MSS boundary affected SEHI where mild conditions that were low voltage as well as pressure injection were desired. The limits of detection were in the range from 0.6-4.2 ng mL(-1). A strategy for optimization was described and the method was applied to the ng mL(-1) analysis of spiked wastewater after simple dilution and centrifugation.
Publisher: Wiley
Date: 07-11-2014
Abstract: Multidimensional separation where two or more orthogonal displacement mechanisms are combined is a promising approach to increase peak capacity in CE. The combinations allow dramatic improvement of analytical performance since the total peak capacity is given by a product of the peak capacities of all methods. The initial reports were concentrated on the construction of effective connections between capillaries for 2D analysis. Today, 2D and 3D CE systems are now able to separate real complex biological or environmental mixtures with good repeatability, improved resolution with minimal loss of s le. This review will present the developments in the field of multidimensional CE during the last 15 years. The endeavors in this specific field were on the development of interfaces, interface-free techniques including integrated separations, microdevices, and on-line s le concentration techniques to improve detection sensitivity.
Publisher: Elsevier BV
Date: 09-2020
Publisher: Elsevier BV
Date: 11-2021
Publisher: Elsevier BV
Date: 12-2008
DOI: 10.1016/J.CHROMA.2008.10.074
Abstract: The operating parameters that affect the performance of analyte focusing by micelle collapse (AFMC) to neutral analytes (i.e., dialkyl phthalates) in normal migration micellar electrokinetic chromatography (NM-MEKC) are examined. NM-MEKC is characterized by an electroosmotic flow greater than the electrophoretic velocity of the micellar pseudostationary phase, and was performed using sodium dodecyl sulfate (SDS) with neutral to high pH electrolytes in fused silica capillaries. AFMC is a recently introduced on-line s le preconcentration technique in capillary electrophoresis that can provide hundreds fold improvement in detection sensitivity. The mechanism of AFMC is based on the analyte transport, release, and accumulation by the moving surfactant micelles [e.g., SDS at concentrations closer to the critical micelle concentration (CMC)] in the s le that dilutes below its CMC into a liquid phase zone. The s le is prepared in a matrix that contains SDS micelles and high mobility anions, where the conductivity of the s le matrix is higher compared to that of the separation solution. The s le injection length, s le and separation solution conductivity ratio, and surfactant micelle concentration in the s le were found to affect the AFMC performance, as well as the effective separation length in NM-MEKC. The use of a different electrolyte salt in the s le and separation solution also affected AFMC NM-MEKC results. In particular, sodium chloride in the s le matrix can induce a micelle-mediated neutral analyte isotachophoretic concentration that is detrimental to the technique.
Publisher: MDPI AG
Date: 08-05-2018
Publisher: Wiley
Date: 2014
Abstract: Bioactive natural products are major sources of lead compounds for drug discovery and pharmaceutical development, therefore, innovative and current separation and characterization techniques are important for these compounds. Here, CE methods applied for the analysis of natural products published during 2011-2012 are reviewed. This is an updated version of an earlier review paper in this journal, which highlighted developments during 2006-2010. The major method developments over the review period centered on derivatization, chiral analysis, modes of detection, stacking or on-line s le concentration, and s le preparation (predominantly using extraction methods). The s les analyzed were herbal products, foods, soil, and biological s les. Developments also occurred in the areas of quality control, toxicology assessment, and enzyme-inhibitor screening. A table that summarizes the areas, source of natural product, nature of the bioactive analyte, CE conditions, LODs, and corresponding reference is provided. A short description on the theory of CE and insights on future activities of CE on natural products are also presented.
Publisher: Elsevier BV
Date: 02-2011
DOI: 10.1016/J.CHROMA.2010.12.095
Abstract: Two-step stacking of organic anions by sweeping and micelle to solvent stacking (MSS) using cationic cetyltrimethylammonium micelles in co-electroosmotic flow (co-EOF) capillary zone electrophoresis (CZE) is described. The co-EOF condition where the direction of the EOF is the same as the test anions was satisfied by positive dynamic coating of a fused silica capillary with hexadimethrine bromide. The strategy was as follows. After conditioning the capillary with the background solution (BGS), a micellar solution (MS) was injected before the s le solution (S). The BGS, MS and S have similar conductivities. Voltage was applied at negative polarity. The analytes in the micelle-free S zone were swept by micelles from the MS. The swept analytes were brought by the micelles to the MSS boundary where the second stacking step was induced by the presence of organic solvent in the BGS. Finally was the separation of concentrated analytes by CZE. The effect of electrolyte concentration in the S, injection time of the MS and the S and surfactant concentration in the MS were studied. A 20-29, 17-33 and 18-21 times increase in peak height sensitivity was obtained for the test hypolipidaemic drugs (gemfibrozil, fluvastatin and atorvastatin), non-steroidal anti-inflammatory drugs (diflunisal, naproxen, ketoprofen, indoprofen and indomethacin), and herbicides (mecoprop and fenoprop), respectively. The LODs (S/N=3) were from 0.05 to 0.55 μg/mL. The intraday and interday repeatabilities (%RSD, n=12) in terms of retention time, corrected peak area, and peak heights was less than 3.6, 8.9, and 10.8%, respectively. The application of sweeping and MSS in co-EOF CZE together with a simple extraction procedure to a waste water s le spiked with the test herbicides was also demonstrated.
Publisher: Elsevier BV
Date: 10-2011
DOI: 10.1016/J.CHROMA.2011.08.028
Abstract: The on-line s le concentration technique, micelle to solvent stacking (MSS), was studied for small organic cations (quaternary ammonium herbicides, β-blocker drugs, and tricyclic antidepressant drugs) in reversed migration micellar electrokinetic chromatography. Electrokinetic chromatography was carried out in fused silica capillaries with a background solution of sodium dodecyl sulfate (SDS) in a low pH phosphate buffer. MSS was performed using anionic SDS micelles in the s le solution for analyte transport and methanol or acetonitrile as organic solvent in the background solution for analyte effective electrophoretic mobility reversal. The solvent also allowed for the separation of the analyte test mixtures. A model for focusing and separation was developed and the mobility reversal that involved micelle collapse was experimentally verified. The effect of analyte retention factor was observed by changing the % organic solvent in the background solution or the concentration of SDS in the s le matrix. With an injection length of 31.9 cm (77% of effective capillary length) for the 7 test drugs, the LODs (S/N=3) of 5-14 ng/mL were 101-346-fold better when compared to typical injection. The linearity (R(2), range=0.025-0.8 μg/mL), intraday and interday repeatability (%RSD, n=10) were ≥0.988, <6.0% and <8.5%, respectively. In addition, analysis of spiked urine s les after 10-fold dilution with the s le matrix yielded LODs=0.02-0.10 μg/mL. These LODs are comparable to published electrophoretic methods that required off-line s le concentration. However, the practicality of the technique for more complex s les will rely on dedicated s le preparation schemes.
Publisher: Elsevier BV
Date: 07-2001
DOI: 10.1016/S0021-9673(01)00772-5
Abstract: Porous sol-gel frits are fabricated in a capillary column by filling it with a solution of 3-(trimethoxysilyl)propyl methacrylate, hydrochloric acid, water, toluene (porogen), and a photoinitiator (Irgacure 1800) and exposing it to UV light at 365 nm for 5 min. The separation column (30 cm x 75 microm I.D.) contains between the inlet and outlet frits a 15-cm packed segment filled with 5-microm silica particles modified with the chiral compound (S)-N-3,5-dinitrobenzoyl-1-naphthylglycine. A detection window (1 mm long) is placed immediately after the outlet frit. To demonstrate the performance of this chiral separation column, mixtures of 16 different amino acids (three of which are not naturally occurring) derivatized with the fluorogenic reagent 4-fluoro-7-nitro-2,1,3-benzoxadiazole were separated by capillary chromatography. The enantiomeric separation of the column results in a resolution ranging from 1.21 to 8.29, and a plate height ranging from 8.7 to 39 microm.
Publisher: American Chemical Society (ACS)
Date: 06-10-2001
DOI: 10.1021/AC0155299
Abstract: Preconcentration effects of solvent gradient and s le stacking are investigated on a photopolymerized sol-gel (PSG) in capillary electrochromatography. The porous PSG monolith has a high mass-transfer rate. This characteristic promotes preconcentration of dilute s les. Plugs of s les more than 2 cm in length prepared in the separation solution (nongradient condition) are injected onto the PSG column. The extent of preconcentration is quite significant, showing up to a 100-fold increase in peak heights of the separated analytes. Even larger preconcentrations are achieved under gradient conditions by dissolving the s le in a matrix with a higher concentration of noneluting solvent (water). For eight alkyl phenyl ketones and four polycyclic aromatic hydrocarbons that serve as neutral test analytes, improvements in peak heights obtained under gradient conditions can be more than a 1000-fold. Indeed, injection of a 91.2-cm plug, which is more than 3 times the total length of the capillary, was possible with only a minor loss in resolution. Five peptides serve as charged test analytes. Nongradient conditions in which the s le is hydrodynamically injected onto the PSG column show sizable preconcentration because of s le stacking. The use of a solvent gradient with the same ionic strength, however, does not appear to have practical value because of destacking caused by the changing organic composition that affects the conductivity. As an alternative preconcentration method, we demonstrate that electric field-enhanced s le injection on the PSG yielded up to a 1000-fold improvement in detection sensitivity for the test peptides.
Publisher: Wiley
Date: 11-01-2011
Abstract: Sweeping improved the peak intensity of neutral analytes (i.e. dialkylphthalates) more than 100‐fold without compromise to separation efficiency in partial‐filling micellar electrokinetic chromatography with electrospray ionization mass spectrometry detection.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 16-10-1998
DOI: 10.1126/SCIENCE.282.5388.465
Abstract: When a neutral analyte zone is injected into a charged pseudostationary phase, the length of the zone is predicted to be narrowed by 1/(1 + k ), where k is the retention factor. The conditions for zone narrowing to occur assume negligible electroosmotic flow, a relatively constant electric field along the capillary column, and no pseudostationary phase in the injected analyte mixture. The theoretically expected concentration enhancement was demonstrated experimentally. Consequently, the detection sensitivity of analytes in micellar electrokinetic chromatography (MEKC) can be improved significantly. For ex le, 9 to 18 parts per billion of an environmentally important racemic herbicide spiked in lake water was separated by MEKC and detected by ultraviolet absorption.
Publisher: Elsevier BV
Date: 05-2001
DOI: 10.1016/S0021-9673(01)00566-0
Abstract: Two on-line s le concentration techniques, s le stacking and sweeping, were evaluated using cationic surfactants as pseudostationary phases in micellar electrokinetic chromatography. As cationic surfactant micelles, tetradecyltrimethylammonium bromide and cetyltrimethylammonium chloride were employed. About 10-fold and 1000-fold increases in detection sensitivity in terms of peak heights were observed by s le stacking and sweeping, respectively, without suppression of the electroosmotic flow. In particular, the concentration limits of detection (S/N=3) for test naphthalenesulfonic acids obtained with sweeping were from 0.96 to 0.47 ppb with UV detection without any preconcentration procedure.
Publisher: Wiley
Date: 20-03-2014
Abstract: The common SDS microemulsion (i.e. 3.3% SDS, 0.8% octane, and 6.6% butanol) and organic solvents were investigated for the stacking of cationic drugs in capillary zone electrophoresis using a low pH separation electrolyte. The s le was prepared in the acidic microemulsion and a high percentage of organic solvent was included in the electrolyte at anodic end of capillary. The stacking mechanism was similar to micelle to solvent stacking where the micelles were replaced by the microemulsion for the transport of analytes to the organic solvent rich boundary. This boundary is found between the microemulsion and anodic electrolyte. The effective electrophoretic mobility of the cations reversed from the direction of the anode in the microemulsion to the cathode in the boundary. Microemulsion to solvent stacking was successfully achieved with 40% ACN in the anodic electrolyte and hydrodynamic s le injection of 21 s at 1000 mbar (equivalent to 30% of the effective length). The sensitivity enhancement factors in terms of peak height and corrected peak area were 15 to 35 and 21 to 47, respectively. The linearity R(2) in terms of corrected peak area were >0.999. Interday precisions (%RSD, n = 6) were 3.3-4.0% for corrected peak area and 2.0-3.0% for migration time. Application to spiked real s le is also presented.
Publisher: Wiley
Date: 30-05-2006
Publisher: Elsevier BV
Date: 12-2001
DOI: 10.1016/S0021-9673(01)01346-2
Abstract: The separation and on-line preconcentration by sweeping of charged analytes in electrokinetic chromatography using a neutral pseudostationary phase is described. Under neutral or basic conditions, the electrophoretic migration of anionic analytes towards the anode is overcome by a high, cathode-directed electroosmotic flow hence, they experience net migration towards the cathode, and the system is run at positive polarity mode. The separation and the retention factor, k, are dependent on both the analyte's electrophoretic mobility and its interaction with the pseudostationary phase. The versatility of the sweeping mechanism is then shown in this system. The charged analyte, prepared in a matrix free of the pseudostationary phase, penetrates the pseudostationary phase zone upon application of voltage. Analyte molecules are consequently accumulated and concentrated. As a demonstration, the separation and preconcentration of phenol derivatives using nonionic surfactants of the alkyl polyoxyethylene ether type (Brij 35 and Brij 58) yielded peak height enhancements up to 100-fold. The efficiency of s le stacking was also found to be improved with the use of a high viscosity background solution.
Publisher: Wiley
Date: 25-08-2017
Abstract: Derivatisation is an integrated part of many analytical workflows to enable separation and detection of the analytes. In CE, derivatisation is adapted in the four modes of pre-capillary, in-line, in-capillary, and post-capillary derivatisation. In this review, we discuss the progress in derivatisation from February 2015 to May 2017 from multiple points of view including sections about the derivatisation modes, derivatisation to improve the analyte separation and analyte detection. The advancements in derivatisation procedures, novel reagents, and applications are covered. A table summarising the 46 reviewed articles with information about analyte, s le, derivatisation route, CE method and method sensitivity is provided.
Publisher: American Chemical Society (ACS)
Date: 16-07-2008
DOI: 10.1021/AC8007835
Abstract: An electroosmotic flow (EOF) controlled counterflow isotachophoretic stacking boundary (cf-ITPSB) system under field lified conditions has been examined as a way to improve the sensitivity of anions separated by capillary zone electrophoresis. The system comprised a high concentration of a high-mobility leading ion (100 mM chloride) and a low concentration of low-mobility terminating ion (1-3 mM MES or CHES) added to the s le in an unmodified fused-silica capillary at pH 8.05, buffered with Tris. Computer simulation studies using the software GENTRANS showed an increase in sensitivity of at least 10-fold over the previous cf-ITPSB system for simple inorganic ions, nitrite and nitrate. The simulations also suggested that the cf-ITPSB became stationary within the capillary and that its stationary position was not adversely affected by the concentration of MES. This was in contrast to experimental results that showed a slow and continual movement of the cf-ITPSB. This was more pronounced at lower concentrations of terminator (i.e., <3 mM) and resulted in a loss of resolution due to the cf-ITPSB being closer to the detector upon separation. This discrepancy was attributed to the change in pH across the capillary due to electrolysis and low buffering capacity in the s le, a phenomenon that cannot be simulated by the GENTRANS software. Replacement of MES with CHES as a lower mobility ion with increased buffer capacity failed to reduce the movement of the cf-ITPSB but did provide a further 3-fold improvement in sensitivity. The potential of this approach for sensitivity enhancement was demonstrated for the co-EOF separation of a mixture of six inorganic and small organic ions, with detection limits at the single-figure nanogram per liter level. These detection limits are 100,000 times better than can be achieved by normal hydrodynamic injection (ions prepared in water) and 250 times better than has been achieved by other online preconcentration approaches. The application of the EOF-controlled cf-ITPSB with counter-EOF separation of two pharmaceutical pollutants, naproxen and diflunisal, was also demonstrated with an improvement in sensitivity of 1000 giving detection limits of 350 ng/L in sewage treatment wastewater without any offline pretreatment.
Publisher: Elsevier BV
Date: 12-1997
Publisher: Elsevier BV
Date: 03-2010
DOI: 10.1016/J.ACA.2010.01.011
Abstract: This study describes the development of a novel fluorescent tag, O-2-[aminoethyl]fluorescein, for the separation of sugars by capillary electrophoresis with fluorescence detection using an argon ion laser. The tag was synthesised using three consecutive steps namely: esterification, alkylation and hydrolysis, specifically designed to offer a flexible way in which to make an assortment of fluorescent tags from cheap and readily available starting reagents (typically less than $1 per g of fluorescent tag). Via this flexible synthetic pathway, O-2-[aminoethyl]fluorescein was designed and synthesised with a spacer group to lower steric effects between the fluorescein backbone and the reducing end of the carbohydrate which were anticipated to improve the reactivity of the tag. The newly synthesised tag, O-2-[aminoethyl]fluorescein was evaluated against structurally similar commercial fluorescent motifs namely fluorescent 5-aminomethylfluorescein and non-fluorescent 5-aminofluorescein. Kinetic studies indicated that O-2-[aminoethyl]fluorescein showed similar labeling efficiencies as 5-aminomethylfluorescein, but were achieved in only 30 min, supporting the notion of improved reactivity of the spacer group. The sensitivity of O-2-[aminoethyl]fluorescein was evaluated using maltoheptaose with a detection limit of 1 nM obtained, which was slightly higher than that of 0.3 nM obtained with 5-aminomethylfluorescein, and was due to its lower quantum yield (0.24) when conjugated to the sugar. The separation performance of the tag was also benchmarked with the two commercial reagents using a range of corn syrup oligosaccharides, from 4 to 10 glucose units, typically found in rice starch. Separations were performed using an electrolyte containing 100 mM boric acid, tris at pH 8.65 as background electrolyte, 30 kV applied voltage, 50 microm I.D. x 40 cm (30 cm effective length) capillary. The novel tag showed better resolution of small oligosaccharides, G3 and G4, than the other two reagents, but slightly worse resolution for the longer oligosaccharides, most likely due to the monovalent charge state of the O-2-[aminoethyl]fluorescein compared to the alent charge of the other two tags.
Publisher: Wiley
Date: 03-2009
Abstract: Fundamental studies on the nanopreparation of neutral analytes in CZE by analyte focusing by micelle collapse (AFMC) are presented. The background solution (BGS) is prepared using an electrolyte salt (i.e. sodium or ammonium acetate). The s le solution of the neutral analytes (S) is prepared using SDS at a concentration above the cmc. To induce AFMC, the conductivity of the S must be greater than the BGS. This was achieved by the addition of the electrolyte salt to the S. Dilution of the micellar carrier from the injected S occurs at the BGS zone closest to the boundary between the S and BGS (micellar dilution zone). The dilution of SDS below the cmc causes the collapse of the micelles with subsequent release of previously bound analyte molecules. The continued transport and release causes the analytes to be accumulated at the micellar dilution zone. This nanopreparative technique is compatible with detection using mass spectrometry and can be utilized as a s le injection step for microfluidic devices. The disadvantage of this technique is that the neutral analytes are not separated after concentration. Here, the effect of retention factor of the analyte, conductivity ratio of the S and BGS, SDS concentration in the S, electrolyte salt (i.e. sodium acetate) concentration in the BGS, and organic modifier content in the BGS were examined. A study on the effect of the s le matrix injection prior to the s le injection to the performance of AFMC-CZE to neutral analytes is also presented.
Publisher: MDPI AG
Date: 26-06-2019
DOI: 10.3390/MOLECULES24132349
Abstract: The search for useful compounds from plants is an important research area. Traditional screening that involves isolation and identification/quantitation is tedious, time consuming, and generates a significant amount of chemical waste. Here, we present a simple, fast, and green strategy to assess ≥0.1% wt/wt quantities of useful compounds in plants/spices using pressurized hot water extraction using a household espresso machine followed by chemical analysis using capillary electrophoresis. Three demonstrations with polygodial, cinnamaldehyde, coumarin, and shikimic acid as target metabolites are shown. Direct analysis of extracts was by the developed micellar electrokinetic chromatography and capillary zone electrophoresis methods. The approach, which can be implemented in less developed countries, can process many s les within a day, much faster than traditional techniques that would normally take at least a day. Finally, 0.8–1.1% wt/wt levels of shikimic acid were found in Tasmanian-pepperberry and Tasmanian-fuschia leaves via the approach.
Publisher: American Chemical Society (ACS)
Date: 08-2008
DOI: 10.1021/AC801258R
Abstract: A dimension for online s le preconcentration in capillary electrophoresis (CE) without modification of current CE commercial instrumentation is introduced. The focusing mechanism is based on the transport, release, and accumulation of molecules bound to micelle carriers that are made to collapse into a liquid phase zone. More than 2 orders of magnitude improvement in detection sensitivity for model steroidal compounds using sodium dodecyl sulfate micelles as carrier is demonstrated.
Publisher: Elsevier BV
Date: 09-2000
DOI: 10.1016/S0021-9673(99)01349-7
Abstract: Three environmentally important phenylurea herbicides (monuron, isoproturon, diuron) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 50 mM sodium dodecyl sulfate, 50 mM phosphoric acid, and 15 mM gamma-cyclodextrin. Three on-line concentration techniques are then evaluated to increase the detection sensitivity of the RM-MEKC system. Stacking with reverse migrating micelles (SRMM, water as the s le solvent) provided the best results among the focusing techniques studied. Using a z-shaped detection cell, more than 500-fold increase in peak height is obtained. As a s le preparation and off-line concentration method, solid-phase extraction (SPE) that further improved detection sensitivity was used in the analysis of spiked tap and pond water. For ex le, 1 parts per billion of each herbicide spiked in tap or pond water was detected by MEKC after SPE and SRMM.
Publisher: American Chemical Society (ACS)
Date: 05-12-2017
DOI: 10.1021/ACS.ANALCHEM.7B03009
Abstract: In proteomics, dodecyl sulfate (DS
Publisher: Wiley
Date: 29-03-2016
Abstract: Simultaneous electrophoretic concentration and separation (SECS) was used as a simple and environmental friendly s le preparation strategy for herbicides in beer s les. An electric field was used to facilitate the separation and concentration of the analytes based on their charge from a 20 mL s le of diluted beer into two separate 20 μL aliquots of an acceptor electrolyte housed inside a micropipette. The anionic organophosphonate and cationic quaternary ammonium herbicides were concentrated in the anodic and cathodic pipette, respectively. Under optimized conditions, SECS was completed in 30 min at an applied voltage of 150 V, which provided analyte concentration factors of up to 90. After s le preparation, the SECS concentrate of cationic and anionic herbicides was analyzed by stacking CE with UV detection and also by LC-MS, respectively. The method detection limit for the diluted and undiluted s le was as low as 3 and 15 ng/mL, respectively. The method was linear over two orders of concentration with repeatability and intermediate precision of better than 5.8 and 7.0%RSD, respectively. Accuracy values were between 91.0-115.1%.
Publisher: Springer Science and Business Media LLC
Date: 03-03-2009
DOI: 10.1007/S00216-009-2646-7
Abstract: Sweeping is a powerful on-line s le preconcentration technique that improves the concentration sensitivity of capillary electrophoresis (CE). This approach is designed to focus the analyte into narrow bands within the capillary, thereby increasing the s le volume that can be injected, without any loss of CE efficiency. It utilizes the interactions between an additive [i.e., a pseudostationary phase (PS) or complexing agent] in the separation buffer and the s le in a matrix that is devoid of the additive used. The accumulation occurs due to chromatographic partitioning, complexation or any interaction between analytes and the additive through electrophoresis. The extent of the preconcentration is dependent on the strength of interaction involved. Both charged and neutral analytes can be preconcentrated. Remarkable improvements--up to several thousandfold--in detection sensitivity have been achieved. This suggests that sweeping is a superior and general approach to on-line s le preconcentration in CE. The focusing mechanism of sweeping under different experimental conditions and its combination with other on-line preconcentration techniques are discussed in this review. The recently introduced techniques of transient trapping (tr-trapping) and analyte focusing by micelle collapse (AFMC) as well as other novel approaches to on-line s le preconcentration are also described.
Publisher: Trans Tech Publications Ltd
Date: 27-10-2010
Publisher: Elsevier BV
Date: 06-2002
DOI: 10.1016/S0021-9673(02)00175-9
Abstract: We prepared different photopolymerized sol-gel (PSG) columns by varying the amount of monomer (methacryloxypropyltrimethoxysilane), porogen (toluene) and catalyst (hydrochloric acid) in the reaction solution containing a photoinitiator (Irgacure 1800). The effects of these variations on the chromatographic behavior of the PSG columns were studied. All of the columns studied exhibited reversed-phase character. The concentration of hydrochloric acid was important for the rigidity of the columns, although it did not affect the separation property. The ratio of monomer solution to porogen was a critical factor in controlling the through-pore size and the surface area of PSG, which were found to significantly affect the separation properties, such as permeability, theoretical plate number, retention time, and separation efficiency, of a mixture of test analytes-thiourea, benzene, and naphthalene. There was no change in the retention order for the test analytes. Short separation times were achieved on PSG columns made from a 10% monomer stock solution and 90% porogen with 1 M hydrochloric acid. Mixtures of polycyclic aromatic hydrocarbons and alkylbenzenes were separated with theoretical plate numbers greater than 100 000 plates/m.
Publisher: Wiley
Date: 05-2009
Abstract: Analyte focusing by micelle collapse is investigated as an on-line s le preconcentration technique in partial-filling MEKC with detection using UV and ESI-MS. Enhancement in peak height sensitivity of more than a 100 was obtained for model alkylphenylketones and dialkylphthalates using analyte focusing by micelle collapse-partial-filling MEKC with UV or ESI-MS detection.
Publisher: Wiley
Date: 30-06-2010
Abstract: Seven food grade antioxidants were resolved by microemulsion electrokinetic chromatography. The antioxidants included propyl gallate, octyl gallate, dodecyl gallate, butylated hydroxyanisole, butylated hydroxytoluene, tert-butylhydroquinone and alpha-tocopherol. They were resolved in 11 min using a low pH microemulsion containing 20% propan-2-ol. Theoretical plates in the range 39,000-95,000 per length of column (38.5 cm) were recorded for the antioxidants. The LODs were calculated to be in the range 9-44 microg/mL (30 s hydrostatic injection and a 50 microm id capillary column). The method can also be used to simultaneously analyse for the synthetic preservatives sorbic acid, benzoic acid, salicylic acid and the parabens. The method was successfully applied to noodles for the determination of butylated hydroxytoluene and propyl gallate and to pharmaceutical supplement tablets for alpha-tocopherol. The in-capillary concentration of butylated hydroxytoluene by sweeping was also demonstrated.
Publisher: MDPI AG
Date: 12-02-2020
DOI: 10.3390/PH13020029
Abstract: Short-chain quinones (SCQs) have been identified as potential drug candidates against mitochondrial dysfunction, which is largely dependent on their reversible redox characteristics of the active quinone core. We recently synthesized a SCQ library of 148 naphthoquinone derivatives and identified 16 compounds with enhanced cytoprotection compared to the clinically used benzoquinone idebenone. One of the major drawbacks of idebenone is its high metabolic conversion in the liver, which significantly restricts its therapeutic activity. Therefore, this study assessed the metabolic stability of the 16 identified naphthoquinone derivatives 1–16 using hepatocarcinoma cells in combination with an optimized reverse-phase liquid chromatography (RP-LC) method. Most of the derivatives showed significantly better stability than idebenone over 6 hours (p 0.001). By extending the side-chain of SCQs, increased stability for some compounds was observed. Metabolic conversion from the derivative 3 to 5 and reduced idebenone metabolism in the presence of 5 were also observed. These results highlight the therapeutic potential of naphthoquinone-based SCQs and provide essential insights for future drug design, prodrug therapy and polytherapy, respectively.
Publisher: Wiley
Date: 26-03-2010
Abstract: CE‐ESI‐MS and CE‐ICP‐MS were implemented for studying three phytosiderophores (mugineic acid, epi‐mugineic acid and deoxymugineic acid) and their metal complexes. Free ligands and ferric complexes were analyzed using the first methodology, while six free metals (Co(II), Cu(II), Fe(III), Mn(II), Ni(II) and Zn(II)) together with the corresponding complexes were investigated by the latter technique. CE separation was realized at a voltage of +25 kV employing a BGE containing 20 mM ammonium bicarbonate at pH 7.2. Both techniques revealed limits of detection in the high nM to low μM range. Standard additions to hydroponic s les of H. distichon, cv. Bodega (spring barley) showed regression coefficients for the metal–ligand complexes ranging from 0.984 to 0.999. Additionally, results of a competitivity study allowed the determination of relative metal–phytosiderophore complex stability constants of deoxymugineic/mugineic acid.
Publisher: American Chemical Society (ACS)
Date: 16-03-1999
DOI: 10.1021/AC9810866
No related grants have been discovered for joselito quirino.