@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 {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 {4753,
	title = {An interface with a linear quadrupole ion guide for an electrospray-ion trap mass spectrometer system},
	journal = {Analytical Chemistry},
	volume = {72},
	number = {22},
	year = {2000},
	note = {ISI Document Delivery No.: 374LNTimes Cited: 30Cited Reference Count: 41},
	month = {Nov},
	pages = {5647-5654},
	type = {Article},
	abstract = {A new ion sampling interface for an electrospray ionization 3D ion trap mass spectrometer system is described. The interface uses linear rf quadrupoles as ion guides and ion traps to enhance the performance of the 3D trap. Trapping ions in the linear quadrupoles is demonstrated to improve the duty cycle of the system. Dipolar excitation of ions trapped in a linear quadrupole is used to eject unwanted ions, A resolution of ejection of up to 254 is demonstrated for protonated reserpine ions (m/z 609.3), A composite waveform with a notch in frequency space is used to eject a wide range of matrix ions and to isolate trace analyte ions in a linear quadrupole before ions are injected into the 3D trap. This is useful to overcome space charge problems in the 3D trap caused by excess matrix ions. For trace reserpine in a 500-fold molar excess of poly(propylene glycol) (PPG), it is demonstrated that the resolution and sensitivity of the 3D trap can be increased dramatically with ejection of the excess PPG matrix ions. In comparison to ejection of matrix ions in the 3D trap with a similar broad-band waveform, a ii-fold increase in sensitivity with a 7 times shorter acquisition time was achieved.},
	keywords = {accumulation, ACCURACY, DIGESTS, DISSOCIATION, FILTERED NOISE FIELD, INJECTION, IONIZATION, PEPTIDES, PROTEINS, storage},
	isbn = {0003-2700},
	url = {<Go to ISI>://000165346800018},
	author = {Cha, B. C. and Blades, M. W. and Douglas, D. J.}
}
@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 {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 = {<Go to ISI>://000074920200007},
	author = {Britz-McKibbin, P. and Kranack, A. R. and Paprica, A. and Chen, D. D. Y.}
}
