ORCID Profile
0000-0001-6780-6859
Current Organisations
University of Leicester
,
King Abdullah International Medical Research Center
,
Avance Clinical
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In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Analytical Chemistry | Separation Science | Analytical Spectrometry | Quality Assurance, Chemometrics, Traceability and Metrological Chemistry | Sensor Technology (Chemical aspects) |
Expanding Knowledge in the Chemical Sciences | Scientific Instruments | Plant Production and Plant Primary Products not elsewhere classified | Human Pharmaceutical Treatments (e.g. Antibiotics) | Expanding Knowledge in Technology
Publisher: Wiley
Date: 11-01-2021
DOI: 10.1111/AJO.13292
Publisher: Informa UK Limited
Date: 22-01-2029
Publisher: Wiley
Date: 26-12-2013
Abstract: The calculation of the first few moments of elution peaks is necessary to determine: the amount of component in the s le (peak area or zeroth moment), the retention factor (first moment), and the column efficiency (second moment). It is a time consuming and tedious task for the analyst to perform these calculations, thus data analysis is generally completed by data stations associated to modern chromatographs. However, data acquisition software is a black box which provides no information to chromatographers on how their data are treated. These results are too important to be accepted on blind faith. The location of the peak integration boundaries is most important. In this manuscript, we explore the relationships between the size of the integration area, the relative position of the peak maximum within this area, and the accuracy of the calculated moments. We found that relationships between these parameters do exist and that computers can be programmed with relatively simple routines to automatize the extraction of key peak parameters and to select acceptable integration boundaries. It was also found that the most accurate results are obtained when the S/N exceeds 200.
Publisher: BMJ
Date: 2022
DOI: 10.1136/BMJOPEN-2021-055217
Abstract: When the COVID-19 pandemic was declared, Governments responded with lockdown and isolation measures to combat viral spread, including the closure of many schools. More than a year later, widespread screening for SARS-CoV-2 is critical to allow schools and other institutions to remain open. Here, we describe the acceptability of a minimally invasive COVID-19 screening protocol trialled by the Western Australian Government to mitigate the risks of and boost public confidence in schools remaining open. To minimise discomfort, and optimise recruitment and tolerability in unaccompanied children, a combined throat and nasal (OP/Na) swab was chosen over the nasopharyngeal swab commonly used, despite slightly reduced test performance. Trialling of OP/Na swabbing took place as part of a prospective observational cohort surveillance study in 79 schools across Western Australia. Swabs were collected from 5903 asymptomatic students and 1036 asymptomatic staff in 40 schools monthly between June and September 2020. PCR testing was performed with a two-step diagnostic and independent confirmatory PCR for any diagnostic PCR positives. Concurrent surveys, collected online through the REDCap platform, evaluated participant experiences of in-school swabbing. 13 988 swabs were collected from students and staff. There were zero positive test results for SARS-CoV-2, including no false positives. Participants reported high acceptability: 71% of students reported no or minimal discomfort and most were willing to be reswabbed (4% refusal rate). OP/Na swabbing is acceptable and repeatable in schoolchildren as young as 4 years old and may combat noncompliance rates by significantly increasing the acceptability of testing. This kind of minimally-invasive testing will be key to the success of ongoing, voluntary mass screening as society adjusts to a new ‘normal’ in the face of COVID-19. Australian New Zealand Clinical Trials Registry—ACTRN12620000922976.
Publisher: Elsevier BV
Date: 07-2012
DOI: 10.1016/J.CHROMA.2012.05.007
Abstract: The significant ergence between the retention of 16 terpene standards on porous graphitized carbon (PGC) and C₁₈ packing materials are illustrated. The PGC surface is shown to provide a selectivity toward shape, polarity, and structure that is not afforded by the C₁₈ surface. This observation is illustrated by plots of the retention factors similar to those typically used to represent 2D-HPLC separations. A geometric approach to factor analysis was used to measure the separation ergence together with the selectivity and the product selectivity factors of closely related species. When a methanol mobile phase was used with the PGC surface, a large fraction of the separation space could be utilized. That is further reflected by a spreading angle of 80.3°. The PGC material was also successful at resolving structural isomers where the C₁₈ phase was not. It was also found that the choice of the mobile phase is important when using this material. A much larger degree of space utilization was seen with methanol than with acetonitrile that displayed a spreading angle of only 40.8°.
Publisher: Elsevier BV
Date: 04-2011
DOI: 10.1016/J.CHROMA.2011.01.078
Abstract: Mixed mode stationary phases utilize secondary retention mechanisms to add a dimensionality to the surface of high performance liquid chromatography (HPLC) adsorbents. This approach was used by several authors to improve the separation performance of single dimension separations. We explored the magnitude of these secondary interactions by performing an off-line two-dimensional (2D)-HPLC separation with a Scherzo SM-C18 column of a β-lactoglobulin tryptic digest with a mobile phase pH of 7 in the first dimension and 2 in the second. Mechanism ergence was determined using the peak capacity and a geometric approach to factor analysis, to measure the correlation. This separation was repeated with a C18 stationary phase as a control. It was found that the C18 column had a correlation coefficient of 0.784, smaller than the mixed mode column, 0.884. This indicated that the retention mechanisms of the C18 column were more ergent under these two pH environments than the mixed mode column. However, the SM-C18 still provided alternative selectivity of the peptides to that of the C18 and could be considered as a good alternative for further 2D-HPLC separations.
Publisher: Elsevier BV
Date: 03-2015
DOI: 10.1016/J.TALANTA.2014.11.037
Abstract: The selection of two high performance liquid chromatography (HPLC) columns with vastly different retention mechanisms is vital for performing effective two-dimensional (2D-) HPLC. This paper reports on a systematic method to select a pair of HPLC columns that provide the most different separations for a given s le. This was completed with the aid of a HPLC simulator that predicted retention profiles on the basis of real experimental data, which is difficult when the contents of s le matrices are largely-or completely-unknown. Peaks from the same compounds must first be matched between chromatograms to compare the retention profiles and optimised 2D-HPLC column selection. In this work, two methods of matching peaks between chromatograms were explored and an optimal pair of chromatography columns was selected for 2D-HPLC. First, a series of 17 antioxidants were selected as an analogue for a coffee extract. The predicted orthogonality of the standards was 39%, according to the fractional surface coverage 'bins' method, which was close to the actual space utilisation of the standard mixture, 44%. Moreover, the orthogonality for the 2D-HPLC of coffee matched the predicted value of 38%. The second method employed a complex s le matrix of urine to optimise the column selections. Seven peaks were confidently matched between chromatograms by comparing relative peak areas of two detection strategies: UV absorbance and potassium permanganate chemiluminescence. It was found that the optimal combinations had an orthogonality of 35% while the actual value was closer to 30%.
Publisher: American Chemical Society (ACS)
Date: 05-01-2021
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.CHROMA.2013.09.069
Abstract: Five methods were used to implement fast gradient separations: constant flow rate, constant column-wall temperature, constant inlet pressure at moderate and high pressures (controlled by a pressure controller),and programmed flow constant pressure. For programmed flow constant pressure, the flow rates and gradient compositions are controlled using input into the method instead of the pressure controller. Minor fluctuations in the inlet pressure do not affect the mobile phase flow rate in programmed flow. There producibilities of the retention times, the response factors, and the eluted band width of six successive separations of the same s le (9 components) were measured with different equilibration times between 0 and 15 min. The influence of the length of the equilibration time on these reproducibilities is discussed. The results show that the average column temperature may increase from one separation to the next and that this contributes to fluctuation of the results.
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.ACA.2014.07.012
Abstract: Sodium polyphosphate is commonly used to enhance chemiluminescence reactions with acidic potassium permanganate through a dual enhancement mechanism, but commercially available polyphosphates vary greatly in composition. We have examined the influence of polyphosphate composition and concentration on both the dual enhancement mechanism of chemiluminescence intensity and the stability of the reagent under analytically useful conditions. The average chain length (n) provides a convenient characterisation, but materials with similar values can exhibit markedly different distributions of phosphate oligomers. There is a minimum polyphosphate chain length (∼6) required for a large enhancement of the emission intensity, but no further advantage was obtained using polyphosphate materials with much longer average chain lengths. Providing there is a sufficient average chain length, the optimum concentration of polyphosphate is dependent on the analyte and in some cases, may be lower than the quantities previously used in routine detection. However, the concentration of polyphosphate should not be lowered in permanganate reagents that have been partially reduced to form high concentrations of the key manganese(III) co-reactant, as this intermediate needs to be stabilised to prevent formation of insoluble manganese(IV).
Publisher: Informa UK Limited
Date: 12-2007
Publisher: Wiley
Date: 11-2009
Abstract: C1 and phenyl-type stationary phases were assessed in terms of their environmental impact on separations using as test solutes polycyclic aromatic hydrocarbons. Methanol (MeOH) and acetonitrile (ACN) mobile-phase gradients were employed. These stationary phases were examined to determine if different physical and chemical properties possessed by these surfaces decreased the organic solvent consumption, and yet maintained peak capacity. The cumulative energy demand (CED) was used to gauge the environmental impact of the separations. The separation of the polycyclic aromatic hydrocarbon test mixture using current methodologies (i.e. a C18/ACN combination) had a CED of 1.13 MJ-eq, and a peak capacity of 27 peaks (resolving 7 of 12 peak pairs with R(s)>1). In comparison, a butyl phenyl stationary phase with a methanol mobile phase had a peak capacity of 26, but with a CED of 0.670 MJ-eq. Monolithic columns containing C18 and C1 phases were also tested. A monolithic C18 column with MeOH had the lowest CED at 0.675 MJ-eq, a peak capacity of 28 peaks and good resolving power (resolving ten peak pairs with R(s)>1), suggesting that this is a viable option with respect to reducing environmental impact for these types of analyses.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4AY02812K
Abstract: A multi-location peak parking protocol was developed for a non-destructive assessment of the axial heterogeneity of in situ modified monoliths. This was tested on a column with a surface coverage density gradient along the length of the monolithic rod. Qualitative changes in band broadening were observed and were consistent with theoretical studies.
Publisher: Elsevier BV
Date: 08-2010
DOI: 10.1016/J.CHROMA.2010.06.002
Abstract: Phenyl type stationary phases of increasing spacer chain length (phenyl, methyl phenyl, ethyl phenyl, propyl phenyl and butyl phenyl, with 0-4 carbon atoms in the spacer chain, respectively) were synthesised and packed in house to determine the impact that the spacer chain length has on the retention process. Two trends in the aromatic selectivity, q(aromatic), were observed, depending on whether the number of carbon atoms in the spacer chain is even or odd. Linear log k' vs phi plots were obtained for each stationary phase and the S coefficient was determined from the gradient of these plots. For the phenyl type phases, the S vs n(c) plots of the retention factors of linear polycyclic aromatic hydrocarbons vs the number of rings exhibit a distinct discontinuity that between 3 and 4 rings, which increases with increasing spacer chain length for even phases but decreases for odd phases. Accordingly, we suggest that the retention factors depend differently on the number of carbon atoms in the spacer chain depending on whether this number is even or odd and that this effect is caused by different orientations of the aromatic ring relative to the silica surface.
Publisher: Brill | Wageningen Academic
Date: 2007
Publisher: Future Science Ltd
Date: 12-2013
DOI: 10.4155/BIO.13.272
Publisher: Elsevier BV
Date: 09-2010
DOI: 10.1016/J.CHROMA.2010.07.007
Abstract: Chromatographic detection responses are recorded digitally. A peak is represented ideally by a Guassian distribution. Raising a Guassian distribution to the power 'n' increases the height of the peak to that power, but decreases the standard deviation by radicaln. Hence there is an increasing disparity in detection responses as the signal moves from low level noise, with a corresponding decrease in peak width. This increases the S/N ratio and increases peak to peak resolution. The ramifications of these factors are that poor resolution in complex chromatographic data can be improved, and low signal responses embedded at near noise levels can be enhanced. The application of this data treatment process is potentially very useful in 2D-HPLC where s le dilution occurs between dimension, reducing signal response, and in the application of post-reaction detection methods, where band broadening is increased by virtue of reaction coils. In this work power functions applied to chromatographic data are discussed in the context of (a) complex separation problems, (b) 2D-HPLC separations, and (c) post-column reaction detectors.
Publisher: Wiley
Date: 31-07-2013
Abstract: A series of experiments was conducted to evaluate the degree of band broadening in very high pressure LC due to column connections. Different column manufacturers use slightly different designs for their column fittings. If the same column connections are repeatedly used to attach columns of different origins, different void volumes form between capillary tubes and column inlets. An Agilent Ultra Low Dispersion Kit (tubing id 75 μm) was installed on an Agilent Infinity 1290 ultra HPLC and used to connect successively an Agilent, a Phenomenex, and a Waters column. A series of uracil (unretained) s les were injected and eluted at a wide range of flow rates with a water/acetonitrile mixture as eluent. In order to determine the variance contribution from column connections as accurately as possible a nonretained probe compound was selected because the variance contribution from the column is the smallest for analytes, which have very low k values. Yet, this effect still has an impact on the resolution for moderately retained compounds (k > 2) for narrow-bore columns packed with fine particles, since variance contributions are additive for linear chromatographic systems. Each injection was replicated five times under the same experimental conditions. Then NanoViper column connections (tubing id 75 μm) were used and the same injections were made. This system was designed to minimize connection void volumes for any column. Band variances were calculated as the second central moment of elution peaks and used to assess the degree of band broadening due to the column connections. Band broadening may increase from 3.8 to 53.9% when conventional metal ferrules were used to join columns to connection sites. The results show that the variance contribution from improper connections can generate as much as 60.5% of the total variance observed. This demonstrates that column connections can play a larger role than the column packing with respect to band dispersion.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 11-05-2021
DOI: 10.1167/TVST.10.6.16
Publisher: Frontiers Media SA
Date: 22-02-2021
DOI: 10.3389/FPUBH.2021.636921
Abstract: Introduction: Amidst the evolving COVID-19 pandemic, understanding the transmission dynamics of the SARS-CoV-2 virus is key to providing peace of mind for the community and informing policy-making decisions. While available data suggest that school-aged children are not significant spreaders of SARS-CoV-2, the possibility of transmission in schools remains an ongoing concern, especially among an aging teaching workforce. Even in low-prevalence settings, communities must balance the potential risk of transmission with the need for students' ongoing education. Through the roll out of high-throughput school-based SARS-CoV-2 testing, enhanced follow-up for in iduals exposed to COVID-19 and wellbeing surveys, this study investigates the dynamics of SARS-CoV-2 transmission and the current psychosocial wellbeing impacts of the pandemic in school communities. Methods: The DETECT Schools Study is a prospective observational cohort surveillance study in 79 schools across Western Australia (WA), Australia. To investigate the incidence, transmission and impact of SARS-CoV-2 in schools, the study comprises three “modules”: Module 1) Spot-testing in schools to screen for asymptomatic SARS-CoV-2 Module 2) Enhanced surveillance of close contacts following the identification of any COVID-19 case to determine the secondary attack rate of SARS-CoV-2 in a school setting and Module 3) Survey monitoring of school staff, students and their parents to assess psycho-social wellbeing following the first wave of the COVID-19 pandemic in WA. Clinical Trial Registration: Trial registration number: ACTRN12620000922976
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.CHROMA.2013.07.067
Abstract: An algorithm was developed to recognize peaks in a multidimensional separation and calculate their cumulative peak area. To find the retention times of peaks in a one dimensional chromatogram, the Savitzky-Golay smoothing filter was used to smooth and find the first through third derivatives of the experimental profiles. Close examination of the shape of these curves informs on the number of peaks that are present and provides starting values for fitting theoretical profiles. Due to the nature of comprehensive multidimensional HPLC, adjacent cut fractions may contain compounds common to more than one cut fraction. The algorithm determines which components were common in adjacent cuts and subsequently calculates the area of a two-dimensional peak profile by interpolating the surface of the 2D peaks between adjacent peaks. This algorithm was tested by calculating the cumulative peak area of a series of 2D-HPLC separations of alkylbenzenes, phenol and caffeine with varied concentrations. A good relationship was found between the concentration and the cumulative peak area.
Publisher: Springer Science and Business Media LLC
Date: 07-12-2013
DOI: 10.1007/S00216-013-7514-9
Abstract: High-performance liquid chromatography with chemiluminescence detection based on the reaction with acidic potassium permanganate and formaldehyde was explored for the determination of neurotransmitters and their metabolites. The neurotransmitters norepinephrine and dopamine were quantified in the left and right hemispheres of rat hippoc us, nucleus accumbens and prefrontal cortex, and the metabolites vanillylmandelic acid, 3,4-dihydrophenylacetic acid, 5-hydroxyindole-3-acetic acid and homovanillic acid were identified in human urine. Under optimised chemiluminescence reagent conditions, the limits of detection for these analytes ranged from 2.5 × 10(-8) to 2.5 × 10(-7) M. For the determination of neurotransmitter metabolites in urine, a two-dimensional high-performance liquid chromatography (2D-HPLC) separation operated in heart-cutting mode was developed to overcome the peak capacity limitations of the one-dimensional separation. This approach provided the greater separation power of 2D-HPLC with analysis times comparable to conventional one-dimensional separations.
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.CHROMA.2013.11.036
Abstract: Using a column packed with fully porous particles, four methods for controlling the flow rates at which gradient elution runs are conducted in very high pressure liquid chromatography (VHPLC) were tested to determine whether reproducible thermal conditions could be achieved, such that subsequent analyses would proceed at nearly the same initial temperature. In VHPLC high flow rates are achieved, producing fast analyses but requiring high inlet pressures. The combination of high flow rates and high inlet pressures generates local heat, leading to temperature changes in the column. Usually in this case a post-run time is input into the analytical method to allow the return of the column temperature to its initial state. An alternative strategy involves operating the column without a post-run equilibration period and maintaining constant temperature variations for subsequent analysis after conducting one or a few separations to bring the column to a reproducible starting temperature. A liquid chromatography instrument equipped with a pressure controller was used to perform constant pressure and constant flow rate VHPLC separations. Six replicate gradient separations of a nine component mixture consisting of acetophenone, propiophenone, butyrophenone, valerophenone, hexanophenone, heptanophenone, octanophenone, benzophenone, and acetanilide dissolved in water/acetonitrile (65:35, v/v) were performed under various experimental conditions: constant flow rate, two sets of constant pressure, and constant pressure operation with a programmed flow rate. The relative standard deviations of the response factors for all the analytes are lower than 5% across the methods. Programming the flow rate to maintain a fairly constant pressure instead of using instrument controlled constant pressure improves the reproducibility of the retention times by a factor of 5, when plotting the chromatograms in time.
Publisher: Bentham Science Publishers Ltd.
Date: 11-05-2007
Publisher: Walter de Gruyter GmbH
Date: 15-09-2021
Abstract: Glucose monitoring is vital in children with persistent hypoglycaemia to reduce the risk of adverse neuro-behavioural outcomes especially in children with hyperinsulinism. The role of continuous glucose monitoring (CGM) systems in monitoring glucose levels in this cohort is limited. The objective of this study was to ascertain the effectiveness of CGM and to evaluate parents’ experience of using CGM for monitoring glucose levels in children with hypoglycaemia. Retrospective analysis of sensor glucose (SG) values from Dexcom G4 CGM with paired finger-prick blood glucose (BG) values was performed to determine the accuracy of CGM. The parent experience of CGM was assessed using a questionnaire administered to families of children with congenital hyperinsulinism currently attending the clinic. SG data from 40 children (median age 6 months) with persistent hypoglycaemia (60% Hyperinsulinism) were analysed. The mean difference between 5,650 paired BG and SG values was 0.28 mmol/L. The sensitivity and specificity of CGM to identify severe hypoglycaemia (BG 3.0 mmol/L) were 54.3% (95% CI: 39.0%, 69.1%) and 97.4% (95% CI: 96.9%, 97.8%) respectively. Parents (n=11) reported less anxiety (n=9), better sleep at night (n=7) and preferred to use CGM for monitoring (n=9). Although the high number of false-positive readings precludes the routine use of CGM in the evaluation of hypoglycaemia, it avoids unnecessary BG testing during normoglycaemia. It is an acceptable tool for parents for monitoring their children who are at risk of hypoglycaemia. Newer CGM systems with improved accuracy at lower glucose levels have the potential to further improve monitoring.
Publisher: BMJ
Date: 24-07-2021
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.JIPH.2019.01.067
Abstract: The triple assortment influenza A(H1N1) virus emerged in spring 2009 and disseminated worldwide, including Saudi Arabia. This study was carried out to characterize Saudi influenza isolates in relation to the global strains and to evaluate the potential role of mutated residues in transmission, adaptation, and the pathogenicity of the virus. Nasopharyngeal s les (n = 6492) collected between September 2009 to March 2011 from patients with influenza-like illness were screened by PCR for influenza A(H1N1). Phylogenetic and Molecular evolutionary analysis were carried out to place the Saudi strains in relation to the global strains followed by Mutation analysis of surface and internal proteins. Concatenated whole-genome phylogenetic analysis along with hemagglutinin (HA) signature changes, that is, Aspartic Acid (D) at position 187, P83S, S203T, and R223Q confirmed that the Saudi strains belong to the antigenic category of A/California/07/2009. However, phylogenetic analysis revealed unusual strains of A(H1N1) circulating in Saudi Arabia, not belonging to any of known clades, appearing in five distinct groups well supported by group-specific mutations and novel mutation complexes. These cases had characteristic inter- and intragroup substitution patterns while few of their closest matches showed up as sporadic cases the world over. Specific mutation patterns were detected within the functional domains of internal proteins PB2, PB1, PA, NP, NS1, and M2 having a putative role in viral fitness and virulence. Bayesian coalescent MCMC analysis revealed that Saudi strains belonged to cluster 2 of A(H1N1)pdm09 and spread a month later as compared to other strains of this cluster. Influenza outbreak in Saudi Arabia during 2009-2011 was caused by atypical strains of influenza A(H1N1)pdm09, probably introduced in this community on multiple occasions. To understand the antigenic significance of these novel point mutations and mutation complexes require functional studies, which will be crucial for risk assessment of emergent strains and defining infection control measures.
Publisher: Elsevier BV
Date: 04-2013
DOI: 10.1016/J.CHROMA.2013.02.012
Abstract: This manuscript evaluates the performance of the Eilers' smoothing algorithm by comparing the third central statistical peak moment of simulated peaks to their true value. Peaks were simulated by imposing an exponentially modified Gaussian peak profile onto a random segment of pre-recorded high performance liquid chromatography baseline. Prior to moment calculation the noise was removed from the simulated curves and the signal was subtracted by the approximated baseline. We found that with a signal to noise ratio of 1000 an 11% relative error was observed between the practical and true third statistical moment. The Eilers' smoothing algorithm was observed to both reduced noise and baseline correct without distorting the shape of the chromatographic peak.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5AY02528A
Abstract: Solvent incompatibility is a limiting factor when implementing 2D-HPLC. A programmed temperature gradient in the first dimension was developed to overcome this limitation by allowing an isocratic separation while maintaining selectivity.
Publisher: Elsevier BV
Date: 15-09-2010
DOI: 10.1016/J.TALANTA.2010.06.065
Abstract: Differences between alkyl, dipole-dipole, hydrogen bonding, and pi-pi selective surfaces represented by non-resonance and resonance pi-stationary phases have been assessed for the separation of 'Ristretto' café espresso by employing 2DHPLC techniques with C18 phase selectivity detection. Geometric approach to factor analysis (GAFA) was used to measure the detected peaks (N), spreading angle (beta), correlation, practical peak capacity (n(p)) and percentage usage of the separations space, as an assessment of selectivity differences between regional quadrants of the two-dimensional separation plane. Although all tested systems were correlated to some degree to the C18 dimension, regional measurement of separation ergence revealed that performance of specific systems was better for certain s le components. The results illustrate that because of the complexity of the 'real' s le obtaining a truly orthogonal two-dimensional system for complex s les of natural origin may be practically impossible.
Publisher: Elsevier BV
Date: 08-2010
DOI: 10.1016/J.CHROMA.2010.04.064
Abstract: The frontal analysis method was used to measure the adsorption isotherms of phenol, 4-chlorophenol, p-cresol, 4-methoxyphenol and caffeine on a series of columns packed with home-made alkyl-phenyl bonded silica particles. These ligands consist of a phenyl ring tethered to the silica support via a carbon chain of length ranging from 0 to 4 atoms. The adsorption isotherm models that fit best to the data account for solute-solute interactions that are likely caused by pi-pi interactions occurring between aromatic compounds and the phenyl group of the ligand. These interactions are the dominant factor responsible for the separation of low molecular weight aromatic compounds on these phenyl-type stationary phases. The saturation capacities depend on whether the spacer of the ligands have an even or an odd number of carbon atoms, with the even alkyl chain lengths having a greater saturation capacity than the odd alkyl chain lengths. The trends in the adsorption equilibrium constant are also significantly different for the even and the odd chain length ligands.
Publisher: Elsevier BV
Date: 03-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5AY00722D
Abstract: A robust technique for the encapsulation of silica-monolithic columns into microfluidic devices. This new approach overcomes the deleterious wall-effects of previous approaches and enables direct fluidic connection to the monolith using standard fittings.
Publisher: Elsevier BV
Date: 15-09-2010
DOI: 10.1016/J.TALANTA.2010.06.066
Abstract: In this study, an activity based screening technique combining two-dimensional liquid chromatography (2DHPLC) with UV-absorbance and chemiluminescence detection was applied to study "Ristretto", "Decaffeinatto" and "Volluto" espresso coffees. This technique, which coupled the separation power of 2DHPLC with the sensitivity and selectivity of the chemiluminescence detection, offers great potential for screening complex s les for antioxidant compounds. Detailed information regarding the complexity of the s le, and the variation between these three coffees could be obtained using this multidimensional-hyphenated method of analysis.
Publisher: Wiley
Date: 05-08-2022
DOI: 10.1111/JPC.15665
Abstract: To determine the frequency of protracted bacterial bronchitis (PBB) in children referred to tertiary care with chronic cough and describe management prior to referral. A retrospective cohort study of all new patients with a history of ≥4 weeks of cough seen at the only tertiary paediatric outpatient respiratory service in Western Australia between July 2018 and June 2019. Medical records were reviewed until a final diagnosis was documented or otherwise for a period of 18 months. PBB was the most common cause and comprised 37.9% of all children referred to tertiary respiratory care with chronic cough. In children with PBB, the median cough duration at the time of first specialist review was 5.1 months (IQR 2.1–12.0 months). The most common referral source of PBB was primary practice (40.9%) and the most common working diagnosis pre‐referral was asthma (15.9%). Seventy‐eight percent of children with PBB had an ongoing cough at their first respiratory review, and of these, only 13.5% had been prescribed 4 weeks of antibiotics prior to their respiratory review. Asthma treatment had been prescribed for 34.0% of children with PBB. PBB is the most common cause of chronic cough in children referred to tertiary respiratory care and is frequently misdiagnosed and undertreated pre‐referral. There is a need to facilitate diagnosis and optimal management of PBB in primary care, which could result in earlier symptom resolution and potentially limit disease progression to bronchiectasis.
Publisher: Springer Science and Business Media LLC
Date: 13-11-2015
Publisher: Informa UK Limited
Date: 22-01-2019
Publisher: Elsevier BV
Date: 08-0012
DOI: 10.1016/J.CHROMA.2010.05.029
Abstract: The retention characteristics of phenyl type stationary phases for reversed phase high performance liquid chromatography are still largely unknown. This paper explores the retention process of these types of stationary phases by examining the retention behaviour of linear PAHs and n-alkylbenzenes on a series of propyl phenyl stationary phases that have changes in their ligand density (1.23, 1.31, 1.97, 2.50 micromol m(-2)). The aromatic and methylene selectivities increased with increasing ligand density until a point where a plateau was observed, overall the propyl phenyl phases had a higher degree of aromatic selectivity than methylene selectivity indicating that these columns are suitable for separations involving aromatic compounds. Also, retention characteristics relating to the size of the solute molecule were observed to be influenced by the ligand density. It is likely that the changing retention characteristics are caused by the different topologies of the stationary phases at different ligand densities. At high ligand densities, the partition coefficient became constant.
Publisher: Springer Science and Business Media LLC
Date: 26-03-2014
Publisher: Wiley
Date: 26-09-2019
DOI: 10.1002/ACN3.50898
Publisher: Elsevier BV
Date: 2012
DOI: 10.1016/J.CHROMA.2011.11.020
Abstract: A 2D comprehensive chromatographic separation of blackberry sage fragrant oil was performed by using HPLC in the first dimension and SFC in the second. A C(18)-bonded silica column eluted with an ACN gradient was used in the HPLC dimension and an amino-bonded silica column eluted with ACN as a modifier in the SFC dimension. This 2D separation was completed in the off-line mode, the fractions from the HPLC column being collected and injected in the SFC column. The retention factors on the two columns have a -0.757 correlation coefficient. The method provides a practical peak capacity of 2400 in 280 min. The first eluted peaks in HPLC are the last ones eluted in SFC and vice versa. The results demonstrate that the coupling of an HPLC and an SFC separation have a great potential for 2D chromatographic separations.
Publisher: Wiley
Date: 19-05-2010
Abstract: In this manuscript, we investigate the importance that must be placed on the selection of standard compounds when undertaking studies to optimize the performance of 2-D-HPLC separations. A geometric approach to factor analysis and a measure of peak density across the separation space were applied to assess localized measures of component distributions within the 2-D separation plane. The results of this analysis of data showed that the measure of separation quality varied markedly, depending on the elution zone for which the test was undertaken. The study concluded that if standards cannot be obtained that adequately describe the entire s le matrix, the s le itself should be used, and also, the separation should be optimized for regions of interest, not necessarily the separation as a whole.
Publisher: Elsevier BV
Date: 04-2017
DOI: 10.1016/J.HUMIMM.2017.03.003
Abstract: To investigate the extent of CCR5 polymorphism in the healthy Saudi population. A total of 321 healthy Saudi in iduals were sequenced using the ion Ampliseq™ Exome kit (Life Technologies, USA) on genomic DNA following manufacturer's protocol. Whole Exome Sequencing (WES) reads were aligned to the human reference genome (hg19 build) with Torrent Suite Software (v5.0.2) and the variants were called using the Torrent Variant Caller plugin (v5.0) and imported into Ion Reporter Server (v5.0) for the annotation. CCR5 coding exons variants were filtered and checked against the NHLBI GO Exome Sequencing Project (NHLBI), NCBI Reference dbSNPs database, 1000 genomes and Exome Aggregation Consortium datasets (ExAC). A total of 475 variants were identified. Table 1 shows polymorphisms/mutations detected within exons that introduced an amino acid change, deletion or copy number variants (CNV). Three mutations are predicted to influence CCR5 function, including the 32bp deletion (Rs333). Four polymorphisms were detected, plus two CNV. This is the first report on sequencing the full CCR5 gene using NGS in the Saudi population. Here we demonstrate seven polymorphisms/mutations that were reported before. All were detected within very low frequency including the delta 32 mutation. However, we report for the first time copy number variants at two CCR5 gene locations 45072265 and 38591712.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B9AY00122K
Publisher: Wiley
Date: 07-05-2022
Abstract: Widely known for its recreational use, the cannabis plant also has the potential to act as an antibacterial agent in the medicinal field. The analysis of cannabis plants roducts in both pharmacological and forensic studies often requires the separation of compounds of interest and/or accurate identification of the whole cannabinoid profile. In order to provide a complete separation and detection of cannabinoids, a new two-dimensional liquid chromatography method has been developed using acidic potassium permanganate chemiluminescence detection, which has been shown to be selective for cannabinoids. This was carried out using a Luna 100 Å CN column and a Poroshell 120 EC-C18 column in the first and second dimensions, respectively. The method has utilized a large amount of the available separation space with a spreading angle of 48.4° and a correlation of 0.66 allowing the determination of more than 120 constituents and mass spectral identification of ten cannabinoids in a single analytical run. The method has the potential to improve research involved in the characterization of sensitive, complex matrices.
Publisher: Wiley
Date: 18-09-2013
Abstract: Two multidimensional HPLC separations of an Australian red wine are presented, >70% of the available separation space was used. A porous graphitic carbon (PGC) stationary phase was used as the first dimension in both separations with both RP core-shell and hydrophilic interaction chromatography fully porous columns used separately in the second dimension. To overcome peak analysis problems caused by signal noise and low detection limits, the data were pre-processed with penalised least-squares smoothing. The PGC × RP combination separated 85 peaks with a spreading angle of 71° and the PGC × hydrophilic interaction chromatography separated 207 peaks with a spreading angle of 80°. Both 2D-HPLC steps were completed in 76 min using a comprehensive stop-and-go approach. A smoothing step was added to peak-picking processes and was able to greatly reduce the number of false peaks present due to noise in the chromatograms. The required thresholds were not able to ignore the noise because of the small magnitude of the peaks 1874 peaks were located in the non-smoothed PGC × RP separation that reduced to 227 peaks after smoothing was included.
Publisher: Informa UK Limited
Date: 22-01-2016
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.FORSCIINT.2014.09.018
Abstract: In-silico optimised two-dimensional high performance liquid chromatographic (2D-HPLC) separations of a model meth hetamine seizure s le are described, where an excellent match between simulated and real separations was observed. Targeted separation of model compounds was completed with significantly reduced method development time. This separation was completed in the heart-cutting mode of 2D-HPLC where C18 columns were used in both dimensions taking advantage of the selectivity difference of methanol and acetonitrile as the mobile phases. This method development protocol is most significant when optimising the separation of chemically similar chemical compounds as it eliminates potentially hours of trial and error injections to identify the optimised experimental conditions. After only four screening injections the gradient profile for both 2D-HPLC dimensions could be optimised via simulations, ensuring the baseline resolution of diastereomers (ephedrine and pseudoephedrine) in 9.7 min. Depending on which diastereomer is present the potential synthetic pathway can be categorized.
Publisher: Elsevier BV
Date: 2012
DOI: 10.1016/J.CHROMA.2011.12.015
Abstract: Elution peaks were generated by summing up a mathematical function and a previously recorded experimental noise. The first three statistical moments of these peaks were calculated using several data processing methods. The results obtained were analyzed. From this analysis, a method is developed for the calculation with a satisfying accuracy of the third moments of these combined signals. The method is applicable to real chromatographic peaks and makes it possible to determine accurate estimates of their third moments. This approach could be helpful for the investigation of the mass transfer processes in chromatographic columns because the third moment provides direct access to the external mass transfer coefficient.
Publisher: Elsevier BV
Date: 03-2010
DOI: 10.1016/J.CHROMA.2009.12.079
Abstract: The performance of the new Kinetex-C(18) column was investigated. Packed with a new brand of porous shell particles, this column has an outstanding efficiency. Once corrected for the contribution of the instrument extra column volume, the minimum values of the reduced plate heights for a number of low molecular weight compounds (e.g., anthracene and naphtho[2,3-a]pyrene) were between 1.0 and 1.3, breaking the legendary record set 3 years ago by Halo-C(18) packed columns. The liquid-solid mass transfer of proteins (e.g., insulin and lyzozyme) is exceptionally fast on Kinetex-C(18) much faster than on the Halo-C(18) column. The different contributions of dispersion and mass transfer resistances to the column efficiency were determined and discussed. The possible reasons for this extremely high column efficiency are discussed.
Publisher: Elsevier BV
Date: 05-2014
DOI: 10.1016/J.CHROMA.2014.03.054
Abstract: A critical aspect in fast gradient separations carried out under constant pressure, in the very high pressure liquid chromatography (VHPLC) mode is that time-based chromatograms may not yield highly reproducible separations. A proposed solution to improve the reproducibility of these separations involves plotting the chromatograms as functions of the volume eluted vs. UV absorbance instead of time vs. UV. To study the consequences of using the volume-based rather than the time-based chromatograms, separations were first performed under low pressures that do not generate significant amounts of heat and for which the variations of the eluent density along the columns are negligible. Secondly, they were performed under very high pressures that do generate heat and measurable variations of the local retention factor and eluent density along the column. Comparison of the results provides estimates of the improvements obtained when volume based chromatograms are used in gradient analyses. Using a column packed with fully porous particles, four different types of methods and several sets for each method were used to perform the gradient elution runs: two sets of constant flow rate operations, four sets of constant pressure operations, two sets of constant pressure operations with programmed flow rate, and one set using the constant heat loss approach. The differences between time-based and volume-based chromatograms are demonstrated by using eight replicates of early, middle, and last eluting peaks. The results show that volume-based chromatograms improve the retention time reproducibility of the four constant pressure methods by a factor of 3.7 on average. If the column is not thermally conditioned prior to performing a long series of separations, flow controlled methods (constant flow rate, programmed constant pressure, and constant wall heat approaches) are more precise. If one gradient run is used to bring the column to a relatively stable temperature, constant pressure separations have a factor of 3 times better reproducibility of retention times with respect to constant flow rate gradient separations.
Publisher: Springer Science and Business Media LLC
Date: 17-08-2021
DOI: 10.1038/S41598-021-96068-2
Abstract: Adaptive optics flood illumination ophthalmoscopy (AO-FIO) is an established imaging tool in the investigation of retinal diseases. However, the clinical interpretation of AO-FIO images can be challenging due to varied image quality. Therefore, image quality assessment is essential before interpretation. An image assessment tool will also assist further work on improving the image quality, either during acquisition or post processing. In this paper, we describe, validate and compare two automated image quality assessment methods the energy of Laplacian focus operator (LAPE not commonly used but easily implemented) and convolutional neural network (CNN effective but more complex approach). We also evaluate the effects of subject age, axial length, refractive error, fixation stability, disease status and retinal location on AO-FIO image quality. Based on analysis of 10,250 images of 50 × 50 μm size, at 41 retinal locations, from 50 subjects we demonstrate that CNN slightly outperforms LAPE in image quality assessment. CNN achieves accuracy of 89%, whereas LAPE metric achieves 73% and 80% (for a linear regression and random forest multiclass classifier methods, respectively) compared to ground truth. Furthermore, the retinal location, age and disease are factors that can influence the likelihood of poor image quality.
Publisher: Wiley
Date: 22-05-2021
DOI: 10.1002/AUR.2545
Abstract: Delays within the motor domain are often overlooked as an early surveillance marker for autism. The present study evaluated motor difficulties and its potential as an early predictive marker for later autism likelihood in a cohort of infants ( N = 96) showing early behavioral signs of autism aged 9–14 months. The motor domain was evaluated using the motor subscales of the Mullen Scales of Early Learning at baseline, and at a 6‐month follow‐up. The Autism Diagnostic Observation Schedule – Toddler Module (ADOS‐T) was completed at follow‐up as a measure of autism likelihood. Motor difficulties were common at baseline, with 63/96 (65.6%) infants scoring very low or below average in the gross motor domain and 29/96 (30.2%) in the fine motor domain. At follow‐up, gross motor difficulties had resolved for many, with 23/63 (36.5%) infants maintaining these difficulties. Fine motor difficulties resolved in fewer infants, with 20/29 (69.0%) continuing to present with fine motor delays at follow‐up. Adjusted linear regression models suggested that fine motor scores at baseline ( β = −0.12, SE = 0.04) and follow‐up ( β = −0.17, SE = 0.05) were associated with higher ADOS‐T scores with difficulties across both timepoints ( β = 5.60, SE = 1.35) the strongest (largest in magnitude) association with ADOS‐T scores of the predictors examined. Motor difficulties are prominent in children displaying emerging signs of autism, with persistent fine motor difficulties predictive of the developing autism phenotype. The findings indicate the potential clinical value of including evaluation of motor skills within early autism surveillance measures. This prospective study evaluated motor development over a 6‐month period in infants showing early behavioral signs of autism. Atypical motor development was a common feature of infants showing early signs of autism and persistent fine motor difficulties were predictive of the emerging autism phenotype.
Publisher: Wiley
Date: 17-06-2014
Abstract: The synthesis and chromatographic behavior of an analytical size mixed-mode bonded silica monolith was investigated. The monolith was functionalized by an in situ modification process of a bare silica rod with chloro(3-cyanopropyl)dimethyl silane and chlorodimethyl propyl phenyl silane solutions. These ligands were selected in order to combine both resonance and nonresonance π-type bonding within a single separation environment. Selectivity studies were undertaken using n-alkyl benzenes and polycyclic aromatic hydrocarbons in aqueous methanol and acetonitrile mobile phases to assess the methylene and aromatic selectivities of the column. The results fit with the linear solvent strength theory suggesting excellent selectivity of the column was achieved. Comparison studies were performed on monolithic columns that were functionalized separately with cyano and phenyl ligands, suggesting highly conjugated molecules were able to successfully exploit both of the π-type selectivities afforded by the two different ligands on the mixed-mode column.
Publisher: Elsevier BV
Date: 04-2014
DOI: 10.1016/J.CHROMA.2014.02.051
Abstract: To achieve the greatest peak capacity in two-dimensional high performance liquid chromatography (2D-HPLC) a gradient should be operated in both separation dimensions. However, it is known that when an injection solvent that is stronger than the initial mobile phase composition is deleterious to peak performance, thus causing problems when cutting a portion from one gradient into another. This was overcome when coupling hydrophilic interaction with reversed phase chromatography by introducing a counter gradient that changed the solvent strength of the second dimension injection. It was found that an injection solvent composition of 20% acetonitrile in water gave acceptable results in one-dimensional simulations with an initial composition of 5% acetonitrile. When this was transferred to a 2D-HPLC separation of standards it was found that a marked improvement in peak shape was gained for the moderately retained analytes (phenol and dimethyl phthalate), some improvement for the weakly retained caffeine and very little change for the strongly retained n-propylbenzene and anthracene which already displayed good chromatographic profiles. This effect was transferred when applied to a 2D-HPLC separation of a coffee extract where the indecipherable retention profile was transformed to a successful application multidimensional chromatography with peaks occupying 71% of the separation space according to the geometric approach to factor analysis.
Publisher: OMICS Publishing Group
Date: 2015
Publisher: Wiley
Date: 17-04-2015
Abstract: This paper explores the analytical figures of merit of two-dimensional high-performance liquid chromatography for the separation of antioxidant standards. The cumulative two-dimensional high-performance liquid chromatography peak area was calculated for 11 antioxidants by two different methods--the areas reported by the control software and by fitting the data with a Gaussian model these methods were evaluated for precision and sensitivity. Both methods demonstrated excellent precision in regards to retention time in the second dimension (%RSD below 1.16%) and cumulative second dimension peak area (%RSD below 3.73% from the instrument software and 5.87% for the Gaussian method). Combining areas reported by the high-performance liquid chromatographic control software displayed superior limits of detection, in the order of 1 × 10(-6) M, almost an order of magnitude lower than the Gaussian method for some analytes. The introduction of the countergradient eliminated the strong solvent mismatch between dimensions, leading to a much improved peak shape and better detection limits for quantification.
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.CHROMA.2013.11.058
Abstract: Five methods for controlling the mobile phase flow rate for gradient elution analyses using very high pressure liquid chromatography (VHPLC) were tested to determine thermal stability of the column during rapid gradient separations. To obtain rapid separations, instruments are operated at high flow rates and high inlet pressure leading to uneven thermal effects across columns and additional time needed to restore thermal equilibrium between successive analyses. The purpose of this study is to investigate means to minimize thermal instability and obtain reliable results by measuring the reproducibility of the results of six replicate gradient separations of a nine component RPLC standard mixture under various experimental conditions with no post-run times. Gradient separations under different conditions were performed: constant flow rates, two sets of constant pressure operation, programmed flow constant pressure operation, and conditions which theoretically should yield a constant net heat loss at the column's wall. The results show that using constant flow rates, programmed flow constant pressures, and constant heat loss at the column's wall all provide reproducible separations. However, performing separations using a high constant pressure with programmed flow reduces the analysis time by 16% compared to constant flow rate methods. For the constant flow rate, programmed flow constant pressure, and constant wall heat experiments no equilibration time (post-run time) was required to obtain highly reproducible data.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.CHROMA.2011.08.088
Abstract: Several simple techniques are presented for the identification of the boundaries of chromatographic peaks. These methods provide a significant reduction in the time needed to perform the rapid, automatic calculation of the central peak moments and to evaluate the quality of a separation while improving the accuracy of the measurements of column efficiencies. It was found that the identification of the peak boundaries as functions of the peak widths and the examination of the slope of the signal to noise versus time plot are viable alternatives to a manual determination.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B922759H
Abstract: An algorithm was developed for 2DHPLC that automated the process of peak recognition, measuring their retention times, and then subsequently plotting the information in a two-dimensional retention plane. Following the recognition of peaks, the software then performed a series of statistical assessments of the separation performance, measuring for ex le, correlation between dimensions, peak capacity and the percentage of usage of the separation space. Peak recognition was achieved by interpreting the first and second derivatives of each respective one-dimensional chromatogram to determine the 1D retention times of each solute and then compiling these retention times for each respective fraction 'cut'. Due to the nature of comprehensive 2DHPLC adjacent cut fractions may contain peaks common to more than one cut fraction. The algorithm determined which components were common in adjacent cuts and subsequently calculated the peak maximum profile by interpolating the space between adjacent peaks. This algorithm was applied to the analysis of a two-dimensional separation of an apple flesh extract separated in a first dimension comprising a cyano stationary phase and an aqueous/THF mobile phase as the first dimension and a second dimension comprising C18-Hydro with an aqueous/MeOH mobile phase. A total of 187 peaks were detected.
Publisher: Wiley
Date: 18-11-2011
Abstract: The multidimensional high-performance liquid chromatography separations of the complex s le matrix found in café espresso coffee were completed on the propyl phenyl and butyl phenyl columns that contain 3 and 4 carbon atoms in the spacer chain, respectively. Phenyl type stationary phases are able to undergo unique π-π interactions with aromatic compounds. Previous works have found that there are differences in retention characteristics between these chain lengths and this was explored further here. It was found that when analysing the separations by quadrants, using a geometric approach to factor analysis and by measuring the normalised mean radius, subtle differences in the separations were observed and the butyl phenyl phase was more selective for the high to medium polarity species. However, there was very little difference in separation behaviour for the hydrophobic components within the coffee s le. Overall, the analysis of the entire separation showed very little difference.
Publisher: Wiley
Date: 08-11-2020
DOI: 10.1111/JCPP.13349
Abstract: Birth order effects have been linked to variability in intelligence, educational attainment and sexual orientation. First‐ and later‐born children have been linked to an increased likelihood of an Autism Spectrum Disorder (ASD) diagnosis, with a smaller body of evidence implicating decreases in cognitive functioning with increased birth order. The present study investigated the potential association between birth order and ASD diagnostic phenotypes in a large and representative population s le. Data were obtained from an ongoing prospective diagnostic registry, collected between 1999 and 2017, including children (1–18 years of age, n = 5,404) diagnosed with ASD in the state of Western Australia. Children with ASD were ranked relative to sibling’s birth to establish birth order within families at time of ASD diagnosis. Information reported to the registry by health professionals at the time of diagnostic evaluation included demographic and family characteristics, functional abilities and intellectual capacity. Adaptive functioning and intelligence scores decreased with increasing birth order, with later‐born children more likely to have an intellectual disability. Compared to first‐born children with siblings, first‐born children without siblings at the time of diagnosis also exhibited decreased cognitive functioning. These findings demonstrate for the first time an association between increasing birth order and variability in ASD clinical phenotypes at diagnosis, with potential evidence of reproductive curtailment in children without siblings. Taken together, these findings have significant implications for advancing understanding about the potential mechanisms that contribute to heterogeneity in ASD clinical presentations as a function of birth order and family size.
Location: No location found
Location: United Kingdom of Great Britain and Northern Ireland
Location: Saudi Arabia
Location: Australia
Start Date: 06-2014
End Date: 12-2016
Amount: $182,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2014
End Date: 06-2017
Amount: $320,000.00
Funder: Australian Research Council
View Funded Activity