@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 {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.}
}
@article {4738,
	title = {Velocity-difference induced focusing of nucleotides in capillary electrophoresis with a dynamic pH junction},
	journal = {Analytical Chemistry},
	volume = {72},
	number = {8},
	year = {2000},
	note = {ISI Document Delivery No.: 304RDTimes Cited: 122Cited Reference Count: 35},
	month = {Apr},
	pages = {1729-1735},
	type = {Article},
	abstract = {Velocity-difference induced focusing (V-DIF) of nucleotides was achieved by using a dynamic pH junction in capillary electrophoresis (CE) with UV detection. The influence of specific analyte properties, such as nucleotide base structure, sugar structure, and degree of phosphorylation, is examined. The pK(a) values and berate complexation with vicinal diols are important factors that caused the focusing. Therefore, the pH and berate content in the sample and background electrolyte can be adjusted to optimize the focusing effect. This method allows the injection of large volumes of sample (similar to 300 nL), resulting in at least 50-fold improvement in concentration sensitivity. The detection limit of 4.0 x 10(-8) M for nucleotides can be achieved in favorable conditions. V-DIF can be also applied to nucleotide pool analysis from cell extracts to improve the concentration sensitivity of CE and to reduce the time-consuming steps of desalting and off-line preconcentration that are often required for assays of nucleotides from biological samples.},
	keywords = {DNA-ADDUCTS, ELECTROPHORESIS, INJECTION, ISOTACHOPHORESIS, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, NEUTRAL ANALYTES, SAMPLE SELF-STACKING, SEPARATION, TRIPHOSPHATES, VOLUME, ZONE},
	isbn = {0003-2700},
	url = {<Go to ISI>://000086497200001},
	author = {Britz-McKibbin, P. and Bebault, G. M. and Chen, D. D. Y.}
}
@article {4207,
	title = {Dynamic complexation of solutes in capillary electrophoresis},
	journal = {Electrophoresis},
	volume = {19},
	number = {3},
	year = {1998},
	note = {ISI Document Delivery No.: ZD713Times Cited: 12Cited Reference Count: 28},
	month = {Mar},
	pages = {383-387},
	type = {Article},
	abstract = {The analyte migration behavior in any chemical separation system can be described using a single equation that unifies all areas of separation science. This equation can be used in capillary electrophoresis (CE) to design separation systems, and to study interactions between analytes and additives. By using individual capacity factors for each analyte species present in the system, and with the knowledge of the characteristics of each interaction, one can predict the analyte migration behavior in complicated CE systems, including systems with multiple 1:1 interactions and/or higher order interactions.},
	keywords = {AFFINITY, BETA-CYCLODEXTRIN, BINDING, capacity factor, CHIRAL SEPARATIONS, dynamic complexation capillary electrophoresis, ENANTIOMERS, higher order interactions, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, multiple equilibria, OPTIMIZATION, RESOLUTION, SELECTIVITY, separation theory, TIOCONAZOLE, ZONE ELECTROPHORESIS},
	isbn = {0173-0835},
	url = {<Go to ISI>://000072716000003},
	author = {Bowser, M. T. and Chen, D. D. Y.}
}
@article {4317,
	title = {The effects of a mixture of charged and neutral additives on analyte migration behavior in capillary electrophoresis},
	journal = {Electrophoresis},
	volume = {19},
	number = {3},
	year = {1998},
	note = {ISI Document Delivery No.: ZD713Times Cited: 14Cited Reference Count: 45},
	month = {Mar},
	pages = {388-396},
	type = {Article},
	abstract = {Multicomponent additives, such as derivatized cyclodextrins with various degrees of substitution, can be considered single-component additives as long as the fraction of each component remains constant. In this paper, equations are derived describing the effect of such additives on the migration behavior of analytes. These equations are used in the study of capillary electrophoresis (CE) systems with differentially charged cyclodextrins as additives. For weakly acidic analytes, the binding with highly negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) increases their negative electrophoretic mobility, while the binding with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) decreases their negative mobility. By obtaining the equilibrium constants and mobilities for each additive with each analyte (in this case, phenol, 2-naphthol and 1-naphthol), the migration behavior of these analytes in CE systems is quantitatively predicted at various concentrations of mixtures of the two additives. The properties of the contour lines in the binding isotherm surfaces of such CE systems are discussed.},
	keywords = {ANALYTE, ASPECTS, BETA-CYCLODEXTRIN, CHIRAL, ELECTROPHORESIS, MICELLAR ELECTROKINETIC CHROMATOGRAPHY, MIGRATION BEHAVIOR, MOBILE PHASES, multicomponent additives, RESOLUTION, SELECTIVITY, SEPARATION, separation theory, STATIONARY PHASE, THEORETICAL, TIOCONAZOLE ENANTIOMERS, two-additive capillary, ZONE ELECTROPHORESIS},
	isbn = {0173-0835},
	url = {<Go to ISI>://000072716000004},
	author = {Kranack, A. R. and Bowser, M. T. and Britz-McKibbin, P. and Chen, D. D. Y.}
}
