Biomedical subjects

P Britz-McKibbin

Publications and source records attributed to P Britz-McKibbin.

4 recordsLinked to original sources

PubMed2000

Velocity-difference induced focusing of nucleotides in capillary electrophoresis with a dynamic pH junction.

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 pKa values and borate complexation with vicinal diols are important factors that caused the focusing. Therefore, the pH and borate 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 (approximately 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.

Animals↗

PubMed2000

Selective focusing of catecholamines and weakly acidic compounds by capillary electrophoresis using a dynamic pH junction.

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 borate, 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-difference 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 if their chemical properties are known.

Acids↗

PubMed1998

The effects of a mixture of charged and neutral additives on analyte migration behavior in capillary electrophoresis.

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.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed1997

Quantitative description of analyte migration behavior based on dynamic complexation in capillary electrophoresis with one or more additives.

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') in this theory is defined as the product of the equilibrium constant and the additive concentration, thus, k' changes linearly with additive concentration. The net electrophoretic mobility of an analyte is a function of k', 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.

2-Hydroxypropyl-beta-cyclodextrin↗