@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 = {://000185656900009}, author = {Britz-McKibbin, P. and Ichihashi, T. and Tsubota, K. and Chen, D. D. Y. and Terabe, S.} } @article {626, title = {Optimization of cellular nucleotide extraction and sample preparation for nucleotide pool analyses using capillary electrophoresis}, journal = {Journal of Chromatography B-Analytical Technologies in the Biomedical and Life Sciences}, volume = {788}, number = {1}, year = {2003}, note = {ISI Document Delivery No.: 664KCTimes Cited: 12Cited Reference Count: 28}, month = {May}, pages = {103-111}, type = {Article}, abstract = {Cell extraction and further sample preparation for nucleotide pool analysis using capillary electrophoresis was faster and simpler using volatile extraction solvents (e.g. organic solvents and de-ionized water) compared to the commonly applied acids dissolved in water (e.g. perchloric acid and trichloracetic acid). Temperature had to be controlled during the whole sample preparation process to prevent degradation, and extracts had to be cleaned from proteins and other large molecules prior to capillary electrophoretic analysis to improve reproducibility. Capillary electrophoresis using borate and cyclodextrins in the background electrolyte was used for determining 11 cellular nucleotides simultaneously. In order to optimize the assay, 0-100\% acetonitrile, 0-100\% ethanol, and 0-100\% methanol in de-ionized water were applied to extract nucleotides from mouse lymphoma cells, and nucleotide yields, recovery, and reproducibility were compared. The assay met the commonly accepted validation limits for biological fluids, if 20-80\% acetonitrile in water and 40-60\% ethanol in water were used as extraction solvents. (C) 2003 Elsevier Science B.V. All rights reserved.}, keywords = {CELLS, dynamic pH junction, FLUIDS, MIGRATION BEHAVIOR, NUCLEOSIDES, nucleotides, PERFORMANCE LIQUID-CHROMATOGRAPHY, QUANTITATIVE-ANALYSIS, SEPARATION, TISSUES, TRIPHOSPHATES}, isbn = {1570-0232}, url = {://000182059400012}, author = {Grob, M. K. and O{\textquoteright}Brien, K. and Chu, J. 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.} }