@article {https://doi.org/10.1002/elps.202400211, title = {Advances and Applications of Capillary Electrophoresis Mass Spectrometry in Food Analysis: Strategies for Online and Offline Preconcentration}, journal = {ELECTROPHORESIS}, number = {n/a}, year = {2025}, abstract = {

ABSTRACT Advancements in food technology have increased the need for thorough analysis to ensure food safety, quality, and compliance with regulatory requirements. Capillary electrophoresis\–mass spectrometry (CE\–MS) has emerged as a powerful tool in food analysis due to its high separation efficiency, low sample consumption, and ability to handle complex matrices. However, challenges such as the use of volatile running buffers and maintaining the stability of the electrical circuit connecting the CE and MS systems have been addressed through advancements in interface designs, such as sheathless systems and optimized sheath-liquid compositions. Online and offline preconcentration techniques have significantly enhanced CE\–MS sensitivity (up to 1000-fold) through stacking methods such as large volume sample stacking (LVSS) and dynamic pH junction stacking. Meanwhile, offline sample preparation techniques, such as solid-phase extraction (SPE) and liquid-based methods, are essential for removing matrix interferences and preconcentrating targeted analytes. This review explores both online and offline preconcentration methods and emphasizes the importance of CE\–MS in helping researchers develop effective strategies for selecting the best preconcentration methods for food analysis.

}, keywords = {capillary electrophoresis, food, interfacing techniques, MASS SPECTROMETRY, STACKING}, doi = {https://doi.org/10.1002/elps.202400211}, url = {https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/elps.202400211}, author = {Semail, Nadhiratul-Farihin and Yahaya, Noorfatimah and Mohamed, Ahmad Husaini and Chen, David D. Y. and Zain, Nur Nadhirah Mohamad} } @article {https://doi.org/10.1002/elps.8139, title = {Characterization of Taurocholic Acid Binding With Insulin for Potential Oral Formulation Using Different Methods}, journal = {ELECTROPHORESIS}, volume = {in press}, number = {n/a}, year = {2025}, abstract = {

ABSTRACT In diabetes management, oral formulation of insulin (INS) has the potential to improve safety, convenience, and patient-centered care compared to subcutaneous injections. However, its bioavailability remains limited, necessitating improved delivery strategies. Recent clinical trials indicate that taurocholic acid (TCA) can enhance the bioavailability of oral INS as an absorption enhancer. In this work, electrospray ionization mass spectrometry (ESI-MS) analysis revealed the formation of 1:1\–1:4 INS\–TCA complexes. MS/MS was used to explore the fragmentation pathway of complex ions and confirm binding stability in the gas phase. Circular dichroism spectra showed no clear conformational change in INS upon TCA binding, even though TCA enhanced INS\&$\#$39;s structural stability. Using Taylor dispersion analysis (TDA), we determined the diffusion coefficient and hydrodynamic radius of INS and its complexes. TCA binding was observed to increase INS size in both the 1:1 and 1:2 INS\–TCA complexes. The binding constant of INS and TCA (1.3 \× 103 L/mol) with approximately five binding sites was obtained via pressure-assisted capillary electrophoresis frontal analysis. Molecular docking simulations indicated that TCA binds to external binding sites on the INS B chain (near Ser-B9, Glu-B13, and Phe-B24 residues), consistent with ESI-MS and TDA results. These findings suggest that TCA binding may enhance INS absorption and increase the bioavailability of oral INS therapy.

}, keywords = {capillary electrophoresis, INSULIN, interaction, MASS SPECTROMETRY, taurocholic acid}, doi = {https://doi.org/10.1002/elps.8139}, url = {https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/elps.8139}, author = {Sun, Chang and Wang, Shuanghao and Li, Huihui and Chen, David D. Y.} } @article {https://doi.org/10.1002/elps.202300245, title = {Numerical modeling and experimental optimization of Taylor dispersion analysis with and without an electric field}, journal = {ELECTROPHORESIS}, volume = {45}, number = {n/a}, year = {2024}, month = {06/2024}, pages = {1054 - 1064}, type = {Research}, chapter = {1054}, abstract = {

Abstract Numerical modeling of Taylor dispersion analysis (TDA) was performed using COMSOL Multiphysics to facilitate better and faster optimization of the experimental conditions. Parameters, such as pressure, electric field, diameter, and length of capillary on the TDA conditions, were examined for particles with hydrodynamic radius (Rh) of 2.5\–250\ {\r A}. The simulations were conducted using 25, 50, and 100\ cm length tubes with diameters of 25, 50, and 100\ \µm. It was shown that particles with larger diffusion coefficients gave more accurate results at higher velocities, and in longer and wider columns; particles with smaller diffusion coefficients gave more accurate results at smaller velocities, and in shorter and thinner columns. Moreover, the effect of electric field on the validity and the applicability of TDA was studied using TDA in conjunction with capillary electrophoresis. Diffusion coefficients were obtained using a pressure and the TDA equation and compared with those obtained with a pressure in combination of an electric field for fluorescein, FD4, FD20, FD70, and FD500. We found that TDA can be used with the presence of moderate electrophoretic migration and electroosmotic flow, when appropriate conditions were met.

}, keywords = {capillary electrophoresis, DIFFUSION, hydrodynamic radius, numerical modeling, Taylor dispersion analysis}, doi = {https://doi.org/10.1002/elps.202300245}, url = {https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/elps.202300245}, author = {Chenyakin, Yuri and Chen, David D. Y.} } @article {SEMAIL2022122833, title = {Simultaneous preconcentration and determination of sulfonamide antibiotics in milk and yoghurt by dynamic pH junction focusing coupled with capillary electrophoresis}, journal = {Talanta}, volume = {236}, year = {2022}, pages = {122833}, abstract = {A dynamic pH junction was used in capillary electrophoresis (CE-DAD) to on-line preconcentrate, separate, and determine trace amounts of sulfonamide antibiotics (SAs) in milk and yoghurt samples in this study. A sample matrix with 0.15\% acetic acid and 10\% methanol (MeOH) at a pH of 4.0, and a background electrolyte (BGE) that contained 35~mM sodium citrate with 10\% MeOH at a pH of 8.5, and an acidic barrage of 0.4\% acetic acid with 10\% MeOH at a pH of 2.5 were utilised to achieve a stacking effect for SAs through a dynamic pH junction. Under optimised conditions, the proposed preconcentration method showed good linearity (30{\textendash}500~ng/mL, r2~>=~0.9940), low limits of detection (LODs) of 4.1{\textendash}6.3~ng/mL, and acceptable analytes recovery (81.2{\textendash}106.9\%) with relative standard deviations (RSDs) within 5.3{\textendash}13.7 (n~=~9). The limits of quantification (LOQs) were below the maximum residue limit approved by the European Union (EU) in this type of matrices. Sensitivity enhancement factors of up to 129 were reached with the optimised dynamic pH junction using CE with a diode array detector (DAD). The method was used to determine SAs in fresh milk, low-fat milk, full-cream milk, and yoghurt samples.}, keywords = {capillary electrophoresis, dynamic pH junction, Milk, Online preconcentration, Sulfonamide antibiotics, Yoghurt}, issn = {0039-9140}, doi = {https://doi.org/10.1016/j.talanta.2021.122833}, url = {https://www.sciencedirect.com/science/article/pii/S0039914021007542}, author = {Nadhiratul-Farihin Semail and Aemi Syazwani Abdul Keyon and Bahruddin Saad and Sazlinda Kamaruzaman and Nur Nadhirah Mohamad Zain and Vuanghao Lim and Mazidatulakmam Miskam and Wan Nazwanie Wan Abdullah and Noorfatimah Yahaya and David D.Y. Chen} } @article {https://doi.org/10.1002/elps.202100167, title = {Characterization of capillary inner surface conditions with streaming potential}, journal = {ELECTROPHORESIS}, volume = {42}, number = {n/a}, year = {2021}, month = {10/2021}, pages = {2094 - 2102}, chapter = {2094}, abstract = {

Abstract Streaming potential is created when an electrolyte solution is forced to flow pass a charged surface. For an uncoated fused silica capillary, the streaming potential is measured between the inlet and outlet vials while applying a pressure across the capillary. The changes in streaming potential can be used to characterize the properties of the capillary inner surface. In this work, HCl, NaCl, and NaOH solutions ranging from 0.4 to 6\ mM were used as the background electrolyte (BGE) at temperatures of 15 to 35 \°C for the mesurements. The streaming potential decreases with the increase in BGE concentration, and the trend is amplified at higher temperatures. When buffer solutions in the pH range of 1.5 to 12.7 were used as the BGE, streaming potential was shown to be sensitive to changes in pH but reaches a maximum at around 9.5. At pH \<\ 3.3, no streaming potentials were observed. The pH of zero surface charge (streaming potential equals 0) changes with temperature, and is measured to be 3.3 to 3.1 when the temperature is changed from 15 to 35\°C. Zeta potentials can be calculated from the measured streaming potential, conductivity, and the solution viscosity. Surface charge densities were calculated in this work using the zeta potentials obtained. We demonstrated that capillary surface conditions can significantly change the streaming potential, and with three different solutions, we showed that analyte-dependent adsorption can be monitored and mitigated to improve the peak symmetry and migration times reproducibility.

}, keywords = {capillary electrophoresis, Reproducibility Improvement, Streaming Potential, Surface Characterization}, doi = {https://doi.org/10.1002/elps.202100167}, url = {https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/elps.202100167}, author = {Chenyakin, Yuri and Chen, David D. Y.} } @article {YANG2021122533, title = {Detecting the formation of human c-KIT oncogene promoter G-Quadruplex by Taylor dispersion analysis}, journal = {Talanta}, volume = {233}, year = {2021}, pages = {122533}, abstract = {The formation of G-quadruplex (G4) structures in oncogenic G-rich promoter regions are implicated in their biological functions, especially the inhibition of transcription. The binding of cations is thought to contribute to the stabilization of the G4 formation and competition against the duplex formation in the genomic sequence. Furthermore, it might affect the recognition of DNA-binding proteins. Therefore, measuring the interaction between G4 DNA and cations in a free solution environment is critical for evaluating G4 DNA biological functions. However, how binding to cations (K+ and NH4+) affects the folding equilibrium of the G4 structure remains unclear. In this work, a Taylor dispersion analysis (TDA) method using a capillary electrophoresis (CE) instrument was established for the quantitative characterization of the cation-dependent G4 formation in the human c-KIT oncogene promoter region, as well as diffusivities and hydrodynamic radii of DNA variations before and after folding. Our results showed that both K+ and NH4+ can induce the random-coiled c-KIT DNA to unfold and form a more unstretched intermediate state and then fold into tightly structured G4s with smaller size. The G4 size induced by NH4+ was smaller than that induced by K+ ions, though these two cations induced the c-KIT G4 DNA formation with similar binding constants (order of magnitude around 106~M-1). The TDA method can be widely used for rapid structural analyses of trace amounts of DNA mixtures, which effectively differentiate DNA variations or DNA-ligand complex conformations.}, keywords = {binding constant, c-KIT oncogene, capillary electrophoresis, G-quadruplex, Taylor dispersion analysis}, issn = {0039-9140}, doi = {https://doi.org/10.1016/j.talanta.2021.122533}, url = {https://www.sciencedirect.com/science/article/pii/S0039914021004549}, author = {Yunhe Yang and Yang Yang and Shuangshuang Wang and Huihui Li and David D.Y. Chen} } @article {doi:10.1002/elps.201900456, title = {Application of multisegment injection on quantification of creatinine and standard addition analysis of urinary 5-hydroxyindoleacetic acid simultaneously with creatinine normalization}, journal = {ELECTROPHORESIS}, volume = {41}, number = {n/a}, year = {2020}, pages = {183-193}, abstract = {

Abstract In this paper, the development of a simple dilute-and-shoot method for quantifying urinary creatinine by CE\–ESI\–MS was described. The creatinine analysis time was about 7\ min/sample by conventional single injection (SI) method and can be significantly reduced to less than 2\ min/sample with multi-segment injection (MSI). In addition, the standard addition analysis of 5-hydroxyindole-3-acetic acid (5-HIAA) and creatinine normalization was performed within one run by the MSI technique, and the total analysis time was 14-min faster compared to the SI method for analyzing the same set of samples. The uses of isotopic and non-isotopic internal standards (ISs) were compared. Creatinine-(methyl-13C) and 5-hydroxyindole-4,6,7-D3-3-acetic-D2 acid (5-HIAA-D5) used as isotopic ISs can provide both accurate and precise results. In contrast, 1,5,5-trimethylhydantoin (1,5,5-TH) used as the non-isotopic IS for creatinine may cause a bias of over 13\% in SI method and even worse when the MSI technique was used. Another compound, 2-methyl-3-indoleacetic acid (2-MIAA), was determined not suitable for MSI analysis of 5-HIAA due to endogenous interferences despite its acceptable performance in conventional methods of analysis.

}, keywords = {capillary electrophoresis, creatinine normalization, MASS SPECTROMETRY, multisegment injection, urinary 5-hydroxyindoleacetic acid}, doi = {10.1002/elps.201900456}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/elps.201900456}, author = {Huang, Zi-Ao and Scotland, Kymora B. and Li, Yueyang and Guo, Jian-Ping and McGeer, Patrick L. and Lange, Dirk and Chen, David D. Y.} } @article {HUANG2020122107, title = {Determination of urinary prostaglandin E2 as a potential biomarker of ureteral stent associated inflammation}, journal = {Journal of Chromatography B}, volume = {1145}, year = {2020}, pages = {122107}, abstract = {Ureteral stents are the most widely used surgical implant in urology. However, they may cause adverse effects to patients, including pain, discomfort, and inflammation. In this work, the inflammatory effect of stent placement and the associated elevation of cyclooxygenase-2 (COX-2) expression were observed. Furthermore, a capillary electrophoresis mass spectrometry (CE-MS) based approach was subsequently developed to quantify urinary prostaglandin E2 (PGE2), a COX-2 metabolite known to contribute to inflammatory renal diseases, to further interrogate the role of this pathway. Urine samples were cleaned and preconcentrated by solid-phase extraction (SPE), and an on-line sample stacking method was used for the enrichment of analytes. The accuracy, precision, and specificity of this method were validated. Standard addition methods were performed to assess the reliability of using deuterated internal standards (IS) in compensating the remaining matrix effect after SPE as well as the detector fluctuation. Through the analysis of 32 pig urine samples, a statistically significant increase of PGE2 was observed in the stented group compared to the unstented (P~=~0.01) and the recovered (P~=~0.004) groups. This work determined that stent placement may contribute to COX-2-dependent inflammation and developed a reliable CE-MS based methodology to quantify PGE2 in stented individuals that may further understand the biology of stent-associated inflammation and inform urologic patient management.}, keywords = {capillary electrophoresis, Cyclooxygenase-2, MASS SPECTROMETRY, Prostaglandin E, Ureteral stent associated inflammation}, issn = {1570-0232}, doi = {https://doi.org/10.1016/j.jchromb.2020.122107}, url = {http://www.sciencedirect.com/science/article/pii/S1570023220302981}, author = {Zi-Ao Huang and Kymora B. Scotland and Yueyang Li and Jiahua Tan and Sonia H.Y. Kung and Ben H. Chew and David D.Y. Chen and Dirk Lange} } @article {WANG201894, title = {Optimization of dynamic pH barrage junction focusing for weakly alkaline or zwitterionic analytes in capillary electrophoresis}, journal = {Journal of Chromatography B}, volume = {1095}, year = {2018}, pages = {94 - 102}, abstract = {

Dynamic pH junction focusing prior to electrophoretic separation has been widely used for online pre-concentration of biologically important analytes, which are mostly weakly alkaline/acidic or zwitterionic species such as neurotransmitters, peptides, and proteins. A pH junction is formed when background electrolytes with different pH values are injected sequentially into the separation column of a capillary electrophoresis (CE) system. Unlike the traditional dynamic pH junction configuration with analyte molecules located in a different chemical environment to the separation background electrolyte (BGE), the pH barrage junction has a separate high pH (or low pH) region containing no analyte. Based on Simul 5 Complex simulations and experimental verification with three series of electrolyte combinations, four basic principles for pH barrage junction focusing were identified for its optimization. First, the peak shape after focusing is slightly asymmetric, but this has negligible influence on the analysis result. Second, longer length of the barrage segment is needed for complete focusing with lower concentration of the buffering species. Third, this technique is more advantageous for analytes with relatively high electrophoretic mobility in a capillary without electroosmotic flow. Fourth, provided the analyte region and pH junction buffering species are separated, this quantitative technique is compatible with both optical and mass spectrometric detection.

}, keywords = {capillary electrophoresis, MASS SPECTROMETRY, pH barrage junction, Sample stacking}, issn = {1570-0232}, doi = {https://doi.org/10.1016/j.jchromb.2018.07.023}, url = {http://www.sciencedirect.com/science/article/pii/S1570023218307906}, author = {Lingyu Wang and Wenjun Tong and Chen, David D. Y.} } @article {ELPS:ELPS6157, title = {Improved sensitivity by post-column chemical environment modification of CE-ESI-MS using a flow-through microvial interface}, journal = {ELECTROPHORESIS}, volume = {38}, year = {2017}, month = {06/2017}, pages = {1644{\textendash}1648}, type = {Research}, keywords = {capillary electrophoresis, electrospray ionization, MASS SPECTROMETRY, Peak symmetry, Post-column modification, SENSITIVITY}, issn = {1522-2683}, doi = {10.1002/elps.201600545}, url = {http://dx.doi.org/10.1002/elps.201600545}, author = {Risley, Jessica May and Chen, David Da Yong} } @article {2450, title = {Quantitative analysis of propofol in whole blood using capillary electrophoresis}, journal = {Journal of Chromatography B-Analytical Technologies in the Biomedical and Life Sciences}, volume = {877}, number = {8-9}, year = {2009}, note = {ISI Document Delivery No.: 424NVTimes Cited: 2Cited Reference Count: 19Hui, Yu Raedschelders, Koen Zhang, Hong Ansley, David M. Chen, David D. Y.}, month = {Mar}, pages = {703-709}, type = {Article}, abstract = {We have developed a straightforward capillary electrophoresis method capable of quantifying clinically relevant propofol concentrations in whole blood from patients undergoing aortocoronary bypass grafting with cardiopulmonary bypass. The method utilizes 400 mu L of whole blood and is capable of detecting propofol in the ng/mL range. Factors affecting reproducibility and reliability of analytical results for clinically relevant samples are discussed. The method was used to evaluate propofol concentrations in blood samples from 30 patients. The distribution in the whole blood concentration achieved in patients advocates the need for target-achieved monitoring techniques. (C) 2009 Elsevier B.V. All rights reserved.}, keywords = {Aortocoronary bypass, BIOPHARMACEUTICAL INDUSTRY, BREATH, capillary electrophoresis, Cardiopulmonary bypass, CHROMATOGRAPHY-MASS-SPECTROMETRY, grafting, HUMAN, Method development, PLASMA, POPULATION, Propofol, Whole blood}, isbn = {1570-0232}, url = {://000264574300006}, author = {Hui, Y. and Raedschelders, K. and Zhang, H. and Ansley, D. M. and Chen, D. D. Y.} } @article {2180, title = {Twenty years of interface development for capillary electrophoresis-electrospray ionization-mass spectrometry}, journal = {Analytica Chimica Acta}, volume = {627}, number = {1}, year = {2008}, note = {ISI Document Delivery No.: 358IYTimes Cited: 22Cited Reference Count: 76Maxwell, E. Jane Chen, David D. Y.Sp. Iss. SI}, month = {Oct}, pages = {25-33}, type = {Review}, abstract = {Capillary electrophoresis-electrospray ionization-mass spectrometry has the potential to become a preferred tool for the analysis of biological mixtures and other complex samples. The development of improved interfaces in the past twenty years has been critical in demonstrating the feasibility of this technique. However, a compromise still exists between interfaces that give optimal performance and those that are practical for commercial applications. The first section of this review focuses on the technological advances in CE-ESI-MS as they relate to the key interface features for both sheath-flow and sheathless systems: delivery of the sheath liquid, shaping of the emitter tip, formation of electrical contact, and practicality in terms of ease of use and lifetime. In the second section, we review the fundamental processes that affect interface performance. Because of the complex natures of both capillary electrophoresis and electrospray ionization, flow rate, arrangement of the electrical circuit, electrochemistry, tip geometry and location of electrical contact must all be carefully managed in the design of a successful interface. (C) 2008 Elsevier B.V. All rights reserved.}, keywords = {BEVELED EDGE, capillary electrophoresis, DESIGN, electrospray ionization, EMITTERS, FLOW NANOSPRAY, FUSED-SILICA CAPILLARY, interface development, JUNCTION INTERFACE, LIQUID CHROMATOGRAPHY/MASS SPECTROMETRY, MASS SPECTROMETRY, MICRO-ELECTROSPRAY, SHEATHLESS CAPILLARY, ZONE-ELECTROPHORESIS}, isbn = {0003-2670}, url = {://000259911600003}, author = {Maxwell, E. J. and Chen, D. D. Y.} } @article {573, title = {Velocity-difference induced focusing of xanthine and purine metabolites by capillary electrophoresis using a dynamic pH junction}, journal = {Chromatographia}, volume = {57}, number = {1-2}, year = {2003}, note = {ISI Document Delivery No.: 644GETimes Cited: 15Cited Reference Count: 45}, month = {Jan}, pages = {87-93}, type = {Article}, abstract = {Velocity-difference induced focusing (V-DIF) of analytes by a dynamic pH junction represents a simple yet effective on-line preconcentration method to improve concentration sensitivity in capillary electrophoresis (CE), Differences in buffer type, pH and conductivity between sample and background electrolyte (BGE) segments of the capillary are properties used to optimize purine focusing within a multi-section electrolyte system. This method permits the injection of large volumes of sample (up to 450 nL or about 18\% of capillary length), resulting in over a 50-fold improvement in sensitivity with baseline resolution. The limit of detection (S/N = 3) for xanthine is determined to less than 4,0 x 10(-8) M under optimum conditions when using UV detection. Analysis of micromolor amounts of xanthine in pooled urine is also demonstrated without sample pretreatment. A dual mechanism involving dynamic pH and isotachophoretic modes is proposed to enhance analyte focusing performance when employing buffer pH junctions based on different types of electrolyte co-ions.}, keywords = {AMPLIFIED SAMPLE STACKING, BIOLOGICAL-FLUIDS, capillary electrophoresis, dynamic pH junction, ELECTROOSMOTIC FLOW, induced focusing, INJECTION, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, NEUTRAL ANALYTES, ON-COLUMN TRANSIENT, purine metabolites, SELF-STACKING, urine, velocity-difference, VOLUME, xanthine analysis, ZONE-ELECTROPHORESIS}, isbn = {0009-5893}, url = {://000180908900013}, author = {Britz-McKibbin, P. and Chen, D. D. Y.} } @article {341, title = {Accurately describing weak analyte-additive interactions by capillary electrophoresis}, journal = {Electrophoresis}, volume = {23}, number = {6}, year = {2002}, note = {ISI Document Delivery No.: 536KNTimes Cited: 12Cited Reference Count: 33}, month = {Mar}, pages = {880-888}, type = {Article}, abstract = {When modeling analyte-additive interactions in capillary electrophoresis (CE), it is necessary to correct for all changes in the apparent electrophoretic mobility of an analyte that are not due to specific binding. Current models based on dynamic complexation have corrected for bulk viscosity changes in the background electrolyte (BGE) when additives are used, while assuming negligible changes in the dielectric constant and other physicochemical properties of the solution. In this report, a study of weak interactions between deoxyribonucleotides and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) revealed significant nonideality in binding isotherms. Changes in the dielectric properties of the solution due to the addition of high concentrations of HP-beta-CD to the BGE was observed to alter the electrophoretic mobility of analytes. A relative dielectric correction factor was required to normalize analyte mobilities to a reference state of zero additive concentration. The use of both a relative dielectric factor and a viscosity correction factor was found to increase the accuracy of the model, reflected by a higher degree of correlation between predicted and measured analyte mobilities. This type of correction is particularly relevant when studying weak analyte binding interactions or when using high concentrations of additive in the BGE. This work is vital for accurate determination of weak binding constants and mobility values, as well as providing a deeper understanding of the fundamental parameters influencing a separation in CE.}, keywords = {analyte-additive interactions, BETA-CYCLODEXTRIN, binding isotherms, capillary electrophoresis, CHIRAL SEPARATION, cyclodextrin, deoxyribonucleotides, DYNAMIC COMPLEXATION, ELECTROKINETIC CHROMATOGRAPHY, ELECTROPHORESIS, ENANTIOMERS, MIGRATION BEHAVIOR, MODEL, OPTIMIZATION, QUANTITATIVE DESCRIPTION, viscosity-dielectric corrections factors, weak, ZONE}, isbn = {0173-0835}, url = {://000174699400008}, author = {Britz-McKibbin, P. and Chen, D. D. Y.} } @article {397, title = {Applications of on-line weak affinity interactions in free solution capillary electrophoresis}, journal = {Electrophoresis}, volume = {23}, number = {6}, year = {2002}, note = {ISI Document Delivery No.: 536KNTimes Cited: 26Cited Reference Count: 109}, month = {Mar}, pages = {815-822}, type = {Review}, abstract = {The impressive selectivity offered by capillary electrophoresis can in some cases be further increased when ligands or additives that engage in weak affinity interactions with one or more of the separated analytes are added to the electrophoresis buffer. This on-line affinity capillary electrophoresis approach is feasible when the migration of complexed molecules is different from the migration of free molecules and when separation conditions are nondenaturing. In this review, we focus on applying weak interactions as tools to enhance the separation of closely related molecules, e.g., drug enantiomers and on using capillary electrophoresis to characterize such interactions quantitatively. We describe the equations for binding isotherms, illustrate how selectivity can be manipulated by varying the additive concentrations, and show how the methods may be used to estimate binding constants. On-line affinity capillary electrophoresis methods are especially valuable for enantiomeric separations and for functional characterization of the contents of biological samples that are only available in minute quantities.}, keywords = {affinity capillary electrophoresis, ALPHA(1)-ACID, AMYLOID-P COMPONENT, biomolecular interactions, capillary electrophoresis, CHIRAL SEPARATION, CHROMATOGRAPHY, CONSTANTS, ELECTROKINETIC, enantiomer separation, ENANTIOSELECTIVE PROTEIN, FRONTAL ANALYSIS, GLYCOPROTEIN, isotherms, MEASURE BINDING, PARTIAL-FILLING TECHNIQUE, PROTEIN-BINDING, review, separation methods, ZONE-ELECTROPHORESIS}, isbn = {0173-0835}, url = {://000174699400002}, author = {Heegaard, N. H. H. and Nissen, M. H. and Chen, D. D. Y.} } @article {477, title = {Chiral separation of benzoporphyrin derivative mono- and diacids by laser induced fluorescence-capillary electrophoresis}, journal = {Electrophoresis}, volume = {23}, number = {1}, year = {2002}, note = {ISI Document Delivery No.: 513ZATimes Cited: 9Cited Reference Count: 42}, month = {Jan}, pages = {93-101}, type = {Article}, abstract = {A method for the separation of benzoporphyrin derivative mono- and diacid (BPDMA, BPDDA) enantiomers; by laser induced fluorescence-capillary electrophoresis (LIF-CE) has been developed. By using 300 mm borate buffer, pH 9.2, 25 mm sodium cholate and 10\% acetronitrile as electrolyte, +10 kV electrokinetic sampling injection of 2 s and an applied +20 kV voltage across the ends of a 37 cm capillary (30 cm to the detector, 50 mum ID), all six BPD stereoisomers; were baseline-separated within 20 min. Formation constants, free electrophoretic and complexation mobilities with borate and cholate were determined based on dynamic complexation capillary electrophoresis theory. The BPD enantiomers can be quantitatively determined in the range of 10(-2)-10(-5) mg mL(-1). The correlation coefficients (r(2)) of the least-squares linear regression analysis of the BPD enantiomers are in the range of 0.9914-0.9997. Their limits of detection are 2.18-3.5 x 10(-3) mg mL(-1). The relative standard deviations for the separation were 2.90-4.64\% (n = 10). In comparison with high-performance liquid chromatography (HPLC), CE has better resolution and efficiency. This separation method was successfully applied to the BPD enantiomers obtained from a matrix of bovine serum and from liposomally formulated material as well as from studies with rat, dog and human microsomes.}, keywords = {benzoporphyrin derivative mono- and diacids, BORATE COMPLEXATION, capillary electrophoresis, DYNAMIC COMPLEXATION MODEL, MIGRATION BEHAVIOR, PERFORMANCE LIQUID-CHROMATOGRAPHY, PHOTODYNAMIC THERAPY, PHOTOSENSITIZER, porphyrins, QUANTITATIVE DESCRIPTION, SYSTEM, TUMOR, ZONE ELECTROPHORESIS}, isbn = {0173-0835}, url = {://000173410100014}, author = {Peng, X. J. and Sternberg, E. and Dolphin, D.} } @article {497, title = {Multiple sprayer system for high-throughput electrospray ionization mass spectrometry}, journal = {Rapid Communications in Mass Spectrometry}, volume = {16}, number = {20}, year = {2002}, note = {ISI Document Delivery No.: 604ADTimes Cited: 13Cited Reference Count: 32}, pages = {1982-1990}, type = {Article}, abstract = {

A multiple sprayer electrospray ion source for high-throughput analysis is described. The ion source is comprised of multiple electrospray capillaries, each with an ion lens located near the tip. The electric potentials applied to the ion lenses are used to control the sprayers. The use of ion lenses eliminates the need for mechanical blocking devices to selectively enable or disable the sprayers, and results in a less expensive and more reliable set-up. Sprayers can be enabled or disabled within approximately 50-250 ms when the lens potentials are controlled manually. For simultaneous operation of multiple electrospray capillaries, it is advantageous to orient the capillaries so that the spray from each passes directly in front of the entrance aperture of the mass spectrometer. Copyright (C) 2002 John Wiley Sons, Ltd.

}, keywords = {ARRAYS, capillary electrophoresis, INTERFACE, LIBRARIES, LIQUID CHROMATOGRAPHY/MASS SPECTROMETRY, SEPARATE SAMPLE}, isbn = {0951-4198}, doi = {10.1002/rcm.806}, url = {https://onlinelibrary.wiley.com/doi/full/10.1002/rcm.806}, author = {Schneider, B. B. and Douglas, D. J. and Chen, D. D. Y.} } @article {4924, title = {Collision-induced dissociation of ions within the orifice-skimmer region of an electrospray mass spectrometer}, journal = {Analytical Chemistry}, volume = {72}, number = {4}, year = {2000}, note = {ISI Document Delivery No.: 285HETimes Cited: 38Cited Reference Count: 33}, month = {Feb}, pages = {791-799}, type = {Article}, abstract = {An equation was derived to describe the variation of the gas number density within the region between the orifice and the skimmer of an electrospray ionization mass spectrometer. The equation was used to develop a semiquantitative model to predict the value of orifice voltages that lead to ion fragmentation within this region. This model made it possible to predict the types of solvent adducts observed for analytes at various orifice voltages. In addition, it is shown that a small number of high-energy collisions is equally effective for collision-induced dissociation as compared to a large number of low-energy collisions. Finally, this model is tested with different background electrolyte solutions and a different electrospray mass spectrometer. It is demonstrated that controlled fragmentation studies can be performed on single-quadrupole mass spectrometers, and the proposed model gives a reasonable description of the fragmentation process in both spectrometers.}, keywords = {capillary electrophoresis, CYTOCHROME-C, DYNAMICS, IDENTIFICATION, INTERFACE, IONIZATION, LIQUID-CHROMATOGRAPHY, PROTEINS, SENSITIVITY, SEPARATION}, isbn = {0003-2700}, url = {://000085383000019}, author = {Schneider, B. B. and Chen, D. D. Y.} } @article {4484, title = {Monte Carlo simulation of error propagation in the determination of binding constants from rectangular hyperbolae. 2. Effect of the maximum-response range}, journal = {Journal of Physical Chemistry A}, volume = {103}, number = {1}, year = {1999}, note = {ISI Document Delivery No.: 174NXTimes Cited: 29Cited Reference Count: 55}, month = {Jan}, pages = {197-202}, type = {Article}, abstract = {Many processes dictated by chemical equilibria can be described by rectangular hyperbolae. Fitting chemical responses to rectangular hyperbolas also allows the binding constants for these equilibria to be estimated. Unfortunately, the propagation of error through the different methods of estimating the binding constants is not well understood. Monte Carlo simulations are used to assess the accuracy and precision of binding constants estimated using a nonlinear regression method and three linear plotting methods. The effect of the difference between the physical response of the uncomplexed substrate and the response of the substrate-ligand complex (i.e., the maximum-response range) was demonstrated using errors typical for a capillary electrophoresis system. It was shown that binding constant estimates obtained using nonlinear regression were more accurate and more precise than estimates from when the other regression methods were used, especially when the maximum-response range was small. The precision of the nonlinear regression method correlated well with the curvature of the binding isotherm. To obtain a precise estimate for the binding constant, the maximum-response range needed to be much larger (over 70 times larger for the conditions used in this experiment) than the error present in individual data points.}, keywords = {capillary electrophoresis, CHIRAL SEPARATION, COMPLEXATION MODEL, CONCENTRATION-DEPENDENT TRANSPORT, dynamic, ELIMINATION PROCESSES, MICHAELIS-MENTEN PARAMETERS, MIGRATION BEHAVIOR, QUANTITATIVE DESCRIPTION, THERMODYNAMIC PARAMETERS, TIOCONAZOLE ENANTIOMERS}, isbn = {1089-5639}, url = {://000079042200026}, author = {Bowser, M. T. and Chen, D. D. Y.} } @article {4689, title = {Undercarboxylation of recombinant prothrombin revealed by analysis of gamma-carboxyglutamic acid using capillary electrophoresis and laser-induced fluorescence}, journal = {Febs Letters}, volume = {445}, number = {2-3}, year = {1999}, note = {ISI Document Delivery No.: 175YCTimes Cited: 6Cited Reference Count: 37}, month = {Feb}, pages = {256-260}, type = {Article}, abstract = {The gamma-carboxyglutamic acid (Gla) content of several variants of human prothrombin has been measured by using capillary electrophoresis and laser-induced fluorescence (CE-LIF). Both plasma-derived prothrombin and recombinant prothrombin contain ten residues of Gla per molecule of protein. In contrast, a variant of human prothrombin (containing the second kringle domain of bovine prothrombin) was separated into two populations that differed in their Gla content. Direct measurement of the Gla content showed an association with the presence or absence of the calcium-dependent conformational change that is required for prothombinase function. Thus, the CE-LIF assay is useful in determining the carboxylation status of recombinant proteins. (C) 1999 Federation of European Biochemical Societies.}, keywords = {baby hamster kidney, calcium, capillary electrophoresis, cell, EXPRESSION, FACTOR-X, gamma carboxy glutamic acid, GLUTAMIC-ACID, HUMAN PROTEIN-C, LASER-INDUCED FLUORESCENCE, METAL, PHOSPHOLIPID-BINDING-PROPERTIES, PROTHROMBIN, PURIFICATION, recombinant protein, RESIDUES, VITAMIN-K}, isbn = {0014-5793}, url = {://000079122800007}, author = {Vo, H. C. and Britz-McKibbin, P. and Chen, D. D. Y. and MacGillivray, R. T. A.} } @article {4203, title = {Monte Carlo simulation of error propagation in the determination of binding constants from rectangular hyperbolae. 1. Ligand concentration range and binding constant}, journal = {Journal of Physical Chemistry A}, volume = {102}, number = {41}, year = {1998}, note = {ISI Document Delivery No.: 132EFTimes Cited: 36Cited Reference Count: 50}, month = {Oct}, pages = {8063-8071}, type = {Article}, abstract = {Rectangular hyperbolae have been used both to estimate equilibrium constants and to describe chemical processes dictated by equilibria. The propagation of error from the experimental measurements to the estimated constants, however, has not been well understood. In this paper, simulated experiments are used in a Monte Carlo analysis to compare the distributions of binding constants estimated by various calculation methods under different experimental conditions. The necessity of matching the range of additive (ligand) concentrations to the binding constant of the chemical interaction is demonstrated. It is shown that the relative error in the binding constant estimate is lower when the additive concentrations cover the central to upper portion of the binding isotherm (i.e., where the fraction of analyte complexed is above 0.5). The difference in the slope of the binding isotherm at the lowest and highest additive concentration used for the measurements is a good indicator of the reliability of the binding constant estimated under a specific set of conditions.}, keywords = {1-1 MOLECULAR-COMPLEXES, ASSOCIATION CONSTANTS, capillary electrophoresis, COMPLEXATION MODEL, CONCENTRATION-DEPENDENT TRANSPORT, dynamic, MICHAELIS-MENTEN PARAMETERS, MIGRATION BEHAVIOR, QUANTITATIVE DESCRIPTION, SPECTROPHOTOMETRIC DATA, TIOCONAZOLE ENANTIOMERS}, isbn = {1089-5639}, url = {://000076616800026}, author = {Bowser, M. T. and Chen, D. D. Y.} } @article {4213, title = {Quantitative assay fdr epinephrine in dental anesthetic solutions by capillary electrophoresis}, journal = {Analyst}, volume = {123}, number = {7}, year = {1998}, note = {ISI Document Delivery No.: 102JCTimes Cited: 40Cited Reference Count: 19}, month = {Jul}, pages = {1461-1463}, type = {Article}, abstract = {A simple and robust method for the separation and quantification of epinephrine in dental anesthetic solutions was developed. The method allows the direct injection of high salt solutions without Sample pre-treatment. Large sample plugs (5.7\% of the total capillary length) are used for epinephrine determination by selective analyte focusing in capillary electrophoresis, The concentration detection limit for epinephrine is about 5.0 x 10(-7) M (90 ng ml(-1)) with a commercial UV detector. The separation protocol was validated in terms of its precision, linearity, accuracy and specificity.}, keywords = {analyte focusing, capillary electrophoresis, CHROMATOGRAPHY, dental anesthetic solutions, EPINEPHRINE, INJECTION, LIDOCAINE, SAMPLES, STACKING, TETRACAINE, ZONE ELECTROPHORESIS}, isbn = {0003-2654}, url = {://000074920200007}, author = {Britz-McKibbin, P. and Kranack, A. R. and Paprica, A. and Chen, D. D. Y.} } @article {4100, title = {Quantitative description of analyte migration behavior based on dynamic complexation in capillary electrophoresis with one or more additives}, journal = {Electrophoresis}, volume = {18}, number = {5}, year = {1997}, note = {ISI Document Delivery No.: XC565Times Cited: 48Cited Reference Count: 28}, month = {May}, pages = {706-716}, type = {Article}, abstract = {A comprehensive theory is proposed to describe the migration behavior of analytes in capillary electrophoresis (CE) when one or more additives are present in the buffer solution. This theory amalgamates and extends the previous work done by others. The capacity factor (k{\textquoteright}) in this theory is defined as the product of the equilibrium constant and the additive concentration, thus, k{\textquoteright} changes linearly with additive concentration, The net electrophoretic mobility of an analyte is a function of k{\textquoteright}, therefore, it can be changed by varying the additive concentration. Three parameters are needed to predict the mobility of an analyte in a one-additive CE system: the mobility of the free analyte, the mobility of the complex, and the equilibrium constant for the analyte-additive interaction (which determines the fraction of the free analyte at different additive concentrations). When additives are used, the change in viscosity obscures this relationship, therefore, a viscosity correction factor is required to convert all mobilities to an ideal state where the viscosity remains constant. The migration behavior of an analyte in a solution with multiple additives can be predicted and controlled, once the equilibrium constants of the interactions between the analyte and each of the additives are obtained separately. beta-Cyclodextrin and hydroxypropyl-beta-cyclodextrin are used as additives and the migration behavior of phenol, p-nitrophenol, and benzoic acid are studied as a model system to verify this theory. When the necessary viscosity correction factor is included, the net electrophoretic mobilities of the analytes obtained from experimental results agree with the values predicted by the theory based on dynamic complexation. Although only experiments with one and two additives were carried out to verify the theory, the equations apply to situations when more than two additives are used. The relationship between the theories of electrophoresis and chromatography is clarified.}, keywords = {additives, analyte migration, BEHAVIOR, BETA-CYCLODEXTRIN, BINDING, capillary electrophoresis, CHIRAL RESOLUTION, DYNAMIC COMPLEXATION, ELECTROKINETIC CHROMATOGRAPHY, OPTIMIZATION, SELECTIVITY, SEPARATION, viscosity correction}, isbn = {0173-0835}, url = {://A1997XC56500008}, author = {Peng, X. J. and Bowser, M. T. and BritzMcKibbin, P. and Bebault, G. M. and Morris, J. R. and Chen, D. D. Y.} } @article {3908, title = {Redefining the separation factor: A potential pathway to a unified separation science}, journal = {Electrophoresis}, volume = {18}, number = {15}, year = {1997}, note = {ISI Document Delivery No.: YW557Times Cited: 20Cited Reference Count: 38}, month = {Dec}, pages = {2928-2934}, type = {Article}, abstract = {Understanding the separation process in capillary electrophoresis (CE leads to the unification of the theories for separation science; While the separation of analytes is governed by equilibria in chromatography, and by (centrifugal) field in ultracentrifugation, the separation in CE is governed by both equilibria and (electric) field. Therefore, a comprehensive separation theory that describes the separation process of analytes in CE should be able to describe the separation processes in both chromatography and ultracentrifugation. In this paper, we propose that individual capacity factors for each analyte species be used to describe the migration behavior of an analyte. The effect of field on each analyte species, as well as the effect of equilibria are considered in deriving a generalized equation that is applicable for all separation techniques. The separation factor defined at present does not directly relate to the migration rates of the analytes, and therefore can not be used in a generalized theory. We propose that the ratio of the migration rates of a pair of analytes (gamma) should be used as the separation factor, instead of the ratio of the two capacity factors. When gamma is used to describe the separation of two closely migrating analytes, all separation techniques have the same resolution equation.}, keywords = {BETA-CYCLODEXTRIN, capacity factor, capillary electrophoresis, CHROMATOGRAPHY, ELECTROKINETIC CHROMATOGRAPHY, ELECTROPHORETIC CHIRAL SEPARATIONS, ENANTIOMERS, LIQUID-CHROMATOGRAPHY, PARAMETERS, RESOLUTION, SELECTIVITY, separation factor, TIOCONAZOLE, ULTRACENTRIFUGATION, ZONE ELECTROPHORESIS}, isbn = {0173-0835}, url = {://000071948300033}, author = {Bowser, M. T. and Bebault, G. M. and Peng, X. J. and Chen, D. D. Y.} } @article {3825, title = {Pyrrolic photosensitizers}, journal = {Current Medicinal Chemistry}, volume = {3}, number = {4}, year = {1996}, note = {ISI Document Delivery No.: VE317Times Cited: 21Cited Reference Count: 172}, month = {Aug}, pages = {239-272}, type = {Review}, abstract = {There are three major classes of photosensitizers which can initiate a phototoxic effect to tissues upon irradiation. These are the cationic dyes (Type I Photosensitizer), the psoralens (Type I and II Photosensitizer), and cyclic polypyrrolic compounds (Type II Photosensitizer). The polypyrrolic compounds such as porphyrins have been investigated since the late 1800{\textquoteright}s for their ability to destroy tissue. In the last ten years, compounds such as chlorins and expanded porphyrins have begun to dominate the preclinical field because they can be activated with light at wavelengths tissue does not effectively absorb. The results of these investigation have been reported in more than 10,000 papers in the field covering aspects from mechanisms of action, photophysics, structure activity relationships, new compound development and clinical investigations. With the approval of PHOTOFRIN(R), (porfimer sodium), the first of the pyrrolic compounds to win acceptance by international regulatory bodies and with nearly 10 other second generation compounds undergoing early clinical trials for diseases ranging from esophageal and skin cancers to age related macular degeneration, the field of photodynamic therapy would seem to have a bright future.}, keywords = {BENZOPORPHYRIN DERIVATIVES, capillary electrophoresis, ENDOGENOUS, M-THPC, MOUSE-TUMOR MODEL, PHOTODYNAMIC THERAPY, PHOTOFRIN-II, PLASMA-LIPOPROTEINS, PROTOPORPHYRIN, RING-A BPD, TISSUE DISTRIBUTION}, isbn = {0929-8673}, url = {://A1996VE31700002}, author = {Sternberg, E. and Dolphin, D.} }