@article {2271,
	title = {Behavior of interacting species in vacancy affinity capillary electrophoresis described by mass balance equation},
	journal = {Electrophoresis},
	volume = {29},
	number = {16},
	year = {2008},
	note = {ISI Document Delivery No.: 343MCTimes Cited: 0Cited Reference Count: 42Sun, Ying Fang, Ning Chen, David D. Y.},
	month = {Aug},
	pages = {3333-3341},
	type = {Article},
	abstract = {Vacancy ACE (VACE) is one of the ACE methods, and has been used to study binding interactions between different biomolecules. Thermodynamic binding constants can be estimated with nonlinear regression methods. With a highly efficient computer simulation program (SimDCCE), it is possible to demonstrate the detailed behaviors of each species during the interaction process under different conditions. In this work, thirteen scenarios in four different combinations of migration orders of the free protein, free drug, and complex formed are studied. The detailed interaction process between protein and ligand is discussed and illustrated based on the mass balance equation, also called mass transfer equation. By properly setting the parameters in the simulation model, the influence of different factors during the interaction process can be well understood.},
	keywords = {affinity capillary electrophoresis, binding constant, COMPUTER-SIMULATION, CONSTANTS, DRUG-PROTEIN-BINDING, equation, EXPERIMENTAL VALIDATION, FRONTAL ANALYSIS, HUMAN-SERUM-ALBUMIN, HUMMEL-DREYER, mass balance, method, PERFORMANCE LIQUID-CHROMATOGRAPHY, vacancy affinity capillary electrophoresis, WALL ADSORPTION, ZONE-ELECTROPHORESIS},
	isbn = {0173-0835},
	url = {<Go to ISI>://000258856900008},
	author = {Sun, Y. and Fang, N. 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 = {<Go to ISI>://000259911600003},
	author = {Maxwell, E. J. and Chen, D. D. Y.}
}
@article {1491,
	title = {Analysis of amphetamine, methamphetamine and methylenedioxy-methamphetamine by micellar capillary electrophoresis using cation-selective exhaustive injection},
	journal = {Electrophoresis},
	volume = {27},
	number = {16},
	year = {2006},
	note = {ISI Document Delivery No.: 081RBTimes Cited: 18Cited Reference Count: 40Meng, Pinjia Fang, Ning Wang, Meng Liu, Huwei Chen, David D. Y.},
	month = {Aug},
	pages = {3210-3217},
	type = {Article},
	abstract = {Cation-selective exhaustive injection (CSEI) is used as an on-line concentration method for the high-sensitivity analysis of illicit amphetamines using CE. Optimum conditions for the determination of amphetamine, methamphetamine and methylenedioxy-methamphetamine were investigated. Sodium dodecyl sulfate (25 mM) in 100 mM phosphate buffer (pH 2.9) with 20\% methanol as organic additive was used as the background electrolyte for CE separation. The LOD, based on an S/N of 3:1, was about 0.01 mu g/mL using normal capillary micellar electrokinetic chromatography, while by using CSEI in combination with micellar sweeping the sensitivity increased up to 1000-fold with the LOD lower than 50 pg/mL. The reproducibility of CSEI combined with micellar sweeping for analyzing amphetamines was satisfactory (relative standard deviation around 10\% by using area ratios against an internal standard). This method is highly sensitive and can be used to analyze trace amount amphetamines in human hair.},
	keywords = {amphetamine, AMPLIFIED SAMPLE STACKING, analysis, cation-selective exhaustive injection, CHROMATOGRAPHY, CHROMATOGRAPHY-MASS SPECTROMETRY, ELECTROKINETIC, FLUORESCENCE DETECTION, illicit drug, LIQUID-CHROMATOGRAPHY, methamphetamine, methylenedioxy-methamphetamine, NEUTRAL ANALYTES, ONLINE CONCENTRATION, REVERSE MIGRATING MICELLES, SOLID-PHASE MICROEXTRACTION, ZONE-ELECTROPHORESIS},
	isbn = {0173-0835},
	url = {<Go to ISI>://000240333600007},
	author = {Meng, P. J. and Fang, N. and Wang, M. and Liu, H. W. and Chen, D. D. Y.}
}
@article {1389,
	title = {Behavior of interacting species in capillary electrophoresis described by mass transfer equation},
	journal = {Analytical Chemistry},
	volume = {78},
	number = {6},
	year = {2006},
	note = {ISI Document Delivery No.: 025ZYTimes Cited: 9Cited Reference Count: 30},
	month = {Mar},
	pages = {1832-1840},
	type = {Article},
	abstract = {Affinity capillary electrophoresis (ACE) has been used to estimate thermodynamic constants of binding interactions with linear or nonlinear regression methods. The accuracy of this approach relies heavily on the binding interaction mechanism, which is controlled by both the nature of the interaction and the experimental conditions. The development of a highly efficient computer-simulated ACE system makes it possible to demonstrate the detailed behavior of any interacting species of a given interaction under any conditions. The order of the mobilities of the complex and the two binding species in their free forms is a key factor to determine what molecules in what locations of the column are involved in the interaction, and the peak shape resulting from such interactions, of a given ACE experiment. In this paper and the supporting materials, 18 scenarios in 6 different combinations of migration orders of the free analyte, free additive, and complex formed are studied by a computer simulation program based on the mass transfer equation. From the study of these situations, we conclude high additive concentration (ensuring high capacity factor) and low analyte concentration (ensuring fast fill-in of the free additive in the analyte plug) are crucial for obtaining accurate results when using the regression methods. On the other hand, the approach to estimate binding constants with computer simulation can be much more accurate as long as accurate and efficient simulation models can be developed, especially when the ratio of the additive and analyte concentrations is not large enough.},
	keywords = {BINDING CONSTANTS, CHROMATOGRAPHY, DISPERSION, EFFICIENCY, ERROR PROPAGATION, MONTE-CARLO-SIMULATION, pressure, RECTANGULAR HYPERBOLAE, SEPARATIONS, ZONE-ELECTROPHORESIS},
	isbn = {0003-2700},
	url = {<Go to ISI>://000236307700015},
	author = {Fang, N. and Chen, D. D. Y.}
}
@article {1107,
	title = {Enumeration algorithm for determination of binding constants in capillary electrophoresis},
	journal = {Analytical Chemistry},
	volume = {77},
	number = {8},
	year = {2005},
	note = {ISI Document Delivery No.: 919FZTimes Cited: 11Cited Reference Count: 16},
	month = {Apr},
	pages = {2415-2420},
	type = {Article},
	abstract = {With more accurate simulation models and more efficient algorithms becoming available, the binding constants of an affinity interaction can be obtained from much simpler experiments using capillary electrophoresis. With the enumeration algorithm, all possible combinations of the binding constant and the complex mobility in certain ranges that could result in the experimental migration time of an injected analyte are extracted from a 3-D surface, which depicts the migration times resulting from different values of the binding constant and the mobility of the complex formed between the interacting pair, to form a 2-D curve. When the experimental conditions are changed, the analyte migration time will also change. A new 2-D curve can be constructed from another 3-D surface on the basis of the pairs of binding constants and complex mobility values that could result in the new migration time. Because the true binding constant and complex mobility values have to be the same for both experimental conditions under the same temperature, there has to be a point where both 2-D curves will converge. The coordinates of the converging point give the values for a binding constant and a complex mobility that will fit all 2-D curves generated under certain experimental conditions. p-Nitrophenol is used as the analyte, beta-cyclodextrin is used as the additive, and a one-cell model is used to simulate affinity CE. The experimental conditions that can improve the accuracy of the binding constants are discussed.},
	keywords = {DYNAMIC COMPLEXATION, ERROR PROPAGATION, MIGRATION BEHAVIOR, MONTE-CARLO-SIMULATION, NUMERICAL-SIMULATION, QUANTITATIVE DESCRIPTION, RANGE, RECTANGULAR HYPERBOLAE, SEPARATION, ZONE-ELECTROPHORESIS},
	isbn = {0003-2700},
	url = {<Go to ISI>://000228605100018},
	author = {Fang, N. and Chen, D. D. Y.}
}
@article {1108,
	title = {General approach to high-efficiency simulation of affinity capillary electrophoresis},
	journal = {Analytical Chemistry},
	volume = {77},
	number = {3},
	year = {2005},
	note = {ISI Document Delivery No.: 893ZGTimes Cited: 12Cited Reference Count: 22},
	month = {Feb},
	pages = {840-847},
	type = {Article},
	abstract = {The differential equation describing electrophoretic migration can be evaluated with various finite difference schemes (FDSs). However, the accuracy and efficiency can be dramatically different depending on the FDS chosen and the way the algorithm is implemented in a computer simulation program. The monotonic transport scheme is used as the algorithm for the hyperbolic part of the differential equation, and the first-order fully explicit scheme is used for the parabolic part of the equation. The combination of these algorithms minimizes the errors and maintains high efficiency. A circular arrangement of the cells in the computer{\textquoteright}s memory is used in the implementation of the algorithms, and the use of concentration thresholds to enable and disable cells along the capillary makes the new algorithm highly efficient. Either thermodynamic or kinetic constants can be used in this program to simulate binding interactions between two species for equilibrium and nonequilibrium affinity CE. Simulation results with various parameters are presented. The simulated peak with proper parameters for an equilibrium affinity CE experiment has shape and position similar to that of the experimental peak. The simulated electropherograms for a nonequilibrium affinity CE experiment also show characteristics of the experimental electropherograms.},
	keywords = {COMPUTER-SIMULATION, ELECTROMIGRATION, EQUILIBRIUM MIXTURES, MATHEMATICAL-MODEL, NUMERICAL-SIMULATION, SEPARATIONS, ZONE-ELECTROPHORESIS},
	isbn = {0003-2700},
	url = {<Go to ISI>://000226759000024},
	author = {Fang, N. and Chen, D. D. Y.}
}
@article {849,
	title = {Determination of shapes and maximums of analyte peaks based on solute mobilitiess in capillary electrophoresis},
	journal = {Analytical Chemistry},
	volume = {76},
	number = {6},
	year = {2004},
	note = {ISI Document Delivery No.: 803IQTimes Cited: 11Cited Reference Count: 28},
	month = {Mar},
	pages = {1708-1714},
	type = {Article},
	abstract = {In capillary electrophoresis, the relative orders of mobilities of analyte, additive, and the complex formed determine the analyte peak shape in a way similar to the way the binding isotherms determine the peak shapes in chromatography. The three mobilities allow six possible orders; each produces a characteristic peak shape in CE. Equations describing the analyte migration in a CE system with the presence of mobility-changing additives can be implemented into computer programs to predict the migration times of the analyte peak maximums, and the predicted migration times agree well with the experimental results.},
	keywords = {DISPERSION, DYNAMIC COMPLEXATION, FLOW, MIGRATION BEHAVIOR, NUMERICAL-SIMULATION, pressure, QUANTITATIVE DESCRIPTION, SEPARATIONS, ZONE-ELECTROPHORESIS},
	isbn = {0003-2700},
	url = {<Go to ISI>://000220225200023},
	author = {Fang, N. and Ting, E. and Chen, D. D. Y.}
}
@article {574,
	title = {Complementary on-line preconcentration strategies for steroids by capillary electrophoresis},
	journal = {Journal of Chromatography A},
	volume = {1013},
	number = {1-2},
	year = {2003},
	note = {ISI Document Delivery No.: 727KJTimes Cited: 47Cited Reference Count: 4416th International Symposium on Microscale Separation and AnalysisJAN 17-22, 2003SAN DIEGO, CALIFORNIA},
	month = {Sep},
	pages = {65-76},
	type = {Proceedings Paper},
	abstract = {Complementary on-line preconcentration strategies are needed when analyzing different classes of solutes in real samples by capillary electrophoresis (CE) with UV detection. The performance of three different on-line preconcentration (focusing) techniques under alkaline conditions was examined in terms of their selectivity and sensitivity enhancement for a group of steroids, including classes of androgens, corticosteroids and estrogens. Electrokinetic focusing of large sample injection plugs (up to 28\% of effective capillary length or 22.1 cm) directly on-capillary can be tuned for specific classes of steroids based on changes in their mobility (velocity) using a multi-section electrolyte system in CE. A dynamic pH junction was applied for the selective resolution and focusing of weakly acidic estrogens using borate, pH 11.0 and pH 8.0 in the background electrolyte and the sample, respectively. Sweeping, using an anionic bile acid surfactant and neutral gamma-cyclodextrin (gamma-CD) under alkaline conditions (pH 8), resulted in focusing and separation of the moderately hydrophobic (non-ionic) classes of steroids, such as androgen and corticosteroids. Optimal focusing and resolution of all test steroids under a single buffer condition was realized by a dynamic pH junction-sweeping format using borate, pH 11.0 and bile acid surfactant with gamma-CD in the BGE, whereas the sample is devoid of surfactant at pH 8.0. The design of selective on-line focusing strategies in CE is highlighted by the analysis of microgram amounts of ethynyl estradiol derived from a female contraceptive pill extract using the dynamic pH junction method, which resulted in over a 100-fold enhancement in concentration sensitivity. (C) 2003 Elsevier B.V. All rights reserved.},
	keywords = {dynamic pH, dynamic pH junction, EPINEPHRINE, FLUORESCENCE DETECTION, INDUCED, INJECTION, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, NEUTRAL ANALYTES, sample preparation, SAMPLE SELF-STACKING, SEPARATION, steroids, sweeping, TAURODEOXYCHOLATE, ZONE-ELECTROPHORESIS},
	isbn = {0021-9673},
	url = {<Go to ISI>://000185656900009},
	author = {Britz-McKibbin, P. and Ichihashi, T. and Tsubota, K. and Chen, D. D. Y. and Terabe, S.}
}
@article {687,
	title = {A quantitative study of continuous flow-counterbalanced capillary electrophoresis for sample purification},
	journal = {Electrophoresis},
	volume = {24},
	number = {17},
	year = {2003},
	note = {ISI Document Delivery No.: 723ZZTimes Cited: 10Cited Reference Count: 25},
	month = {Sep},
	pages = {2887-2895},
	type = {Article},
	abstract = {A systematic evaluation of continuous flow-counterbalanced capillary electrophoresis for microscale preparative applications is presented. The success of the technique was found to depend on the specific nature of the analyte and background electrolyte and was most heavily influenced by factors such as solution conductivity and rate of buffer depletion. The performance of the technique for the system studied was ultimately limited by contamination arising from changes in analyte mobilities during extended run times. Marked improvements in both purification rate and yield were observed using the zwitterionic buffer 2-(N-cyclohexylamino)ethanesulfonic acid when compared to similar runs carried out using a borate background electrolyte. A quantitative evaluation of the technique was performed for the analytes studied and the performance of the technique has been compared to fraction collection methods. The highest recovery achieved was 5.2\% of the fastest migrating component present in the original sample with a resolution of 9 to the adjacent peak and required 100 min under optimized conditions. Recovery could be further increased to 9.0\% in 120 min for the same analyte using pressure-ramped flow-counterbalanced capillary electrophoresis.},
	keywords = {amino acid, BUFFER, DESIGN, flow-counterbalanced capillary electrophoresis, FRACTION COLLECTOR, LASER-INDUCED FLUORESCENCE, MASS-SPECTROMETRY, MEMBRANE, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, PLASMA, PURIFICATION, SAMPLE, SEPARATION, tetramethylrhodamine isothiocyanate, ZONE-ELECTROPHORESIS, zwitterionic buffer},
	isbn = {0173-0835},
	url = {<Go to ISI>://000185462800002},
	author = {McLaren, D. G. 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 = {<Go to ISI>://000180908900013},
	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 = {<Go to ISI>://000174699400002},
	author = {Heegaard, N. H. H. and Nissen, M. H. and Chen, D. D. Y.}
}
@article {368,
	title = {Proton and hydroxide ion mobility in capillary electrophoresis},
	journal = {Analytical Chemistry},
	volume = {74},
	number = {13},
	year = {2002},
	note = {ISI Document Delivery No.: 569FHTimes Cited: 11Cited Reference Count: 22},
	month = {Jul},
	pages = {2938-2942},
	type = {Article},
	abstract = {A capillary electrophoresis method for measuring the effective mobilities of proton and hydroxide ions was developed. Photodiode array detection coupled with pH-indicating dyes enabled the detection of proton and hydroxide ions using a conventional CE instrument. The effects of ionic strength and pH of the background electrolyte on the measurement of effective mobility of the proton were first investigated. Mobility measurements were found to be independent of applied voltage. Hydroxide ion mobility was also measured and found to be in agreement with literature values. The effects of pH indicator and proton source on the ion mobility were determined and are described herein.},
	keywords = {ELECTROLYTE, PH, ZONE-ELECTROPHORESIS},
	isbn = {0003-2700},
	url = {<Go to ISI>://000176589800014},
	author = {Duso, A. B. and Chen, D. D. Y.}
}
@article {4739,
	title = {Selective focusing of catecholamines and weakly acidic compounds by capillary electrophoresis using a dynamic pH junction},
	journal = {Analytical Chemistry},
	volume = {72},
	number = {6},
	year = {2000},
	note = {ISI Document Delivery No.: 295NRTimes Cited: 171Cited Reference Count: 43},
	month = {Mar},
	pages = {1242-1252},
	type = {Article},
	abstract = {A systematic study of selective analyte focusing in a multisection electrolyte system by capillary electrophoresis (CE) is presented. It was found that a dynamic pH junction between sample and background electrolyte zones can be used to focus zwitterionic catecholamines and weakly acidic compounds without the use of special ampholytes. Differences in pH and concentration of complexing agents, such as berate, in the sample and background electrolyte zones were determined to cause focusing through changes in the local velocity of the analyte in two different segments of the capillary. Velocity-differerence induced focusing (V-DIF) of analytes using a dynamic pH junction allowed the injection of large sample volumes and significantly improved the concentration sensitivity of CE. Under optimized conditions, the limit of detection for epinephrine was determined to be about 4 x 10(-8) M (the original sample) with conventional UV absorbance detection. Moreover, separation efficiencies greater than a million theoretical plates can be achieved by focusing such large sample volumes into narrow zones. Multisection electrolyte systems, which lead to the formation of a dynamic pH junction, can be tuned toward improving the concentration sensitivity of specific analytes their chemical properties are known.},
	keywords = {DNA-ADDUCTS, ELECTROCHEMICAL DETECTION, INJECTION, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, MIGRATING MICELLES, NEUTRAL ANALYTES, REVERSE, SAMPLE SELF-STACKING, SEPARATION, VOLUME, ZONE-ELECTROPHORESIS},
	isbn = {0003-2700},
	url = {<Go to ISI>://000085975200021},
	author = {Britz-McKibbin, P. and Chen, D. D. Y.}
}
