Biomedical subjects

C Quang

Publications and source records attributed to C Quang.

4 recordsLinked to original sources

PubMed1995

Extending the scope of chiral separation of basic compounds by cyclodextrin-mediated capillary zone electrophoresis.

In a previous paper on cyclodextrin-mediated capillary zone electrophoresis, it was shown that the use of short-chain tetraalkylammonium cations leads to a reversal in the direction of the electroosmotic flow without an adverse effect on enantioselectivity. As a result, enantiomeric resolution of basic (cationic) compounds can be improved as the electroosmotic flow counteracts the migration of solute enantiomers. It is demonstrated in this report that the scope of chiral separation of basic compounds can be further extended by a combination of reversing the electroosmotic flow and enhancing enantioselectivity through the chemical modifications of beta-cyclodextrin. Therefore, beta-cyclodextrin and its derivatives were evaluated as chiral recognition agents for the chiral separations of 22 basic compounds with rather complex molecular structures. The differences in enantioselectivity displayed by beta-cyclodextrin and derivatives are discussed in order to achieve a better understanding of the chiral interactions involved in the discrimination of solute enantiomers.

Cyclodextrins↗

PubMed1994

Computer-assisted modeling, prediction, and multifactor optimization in micellar electrokinetic chromatography of ionizable compounds.

Previously, the use of phenomenological models to describe the migration behavior of acidic solutes in micellar electrokinetic chromatography (MEKC) was reported. In this paper, the phenomenological approach is further extended by including both acidic and basic solutes and simultaneously taking two important experimental factors (pH and micelle concentration) into consideration. In addition, a general method is described to model the migration behavior of ionizable (both acidic and basic) solutes in MEKC with anionic and cationic micelles. The practical implication of the phenomenological approaches is that they will provide quantitative relationships between solute migration and experimental factors such that the migration behavior can be predicted on the basis of a few initial experiments and that physicochemical parameters of solutes can also be estimated from model fitting. Through computer-assisted modeling, migration behavior of several acidic and basic solutes over a pH-micelle concentration factor space was successfully predicted on the basis of only five experiments. Furthermore, this phenomenological approach was used to predict the separation of a group of aromatic amines in MEKC with anionic micelles, which resulted in a successful separation of 18 aromatic amines in less than 15 min.

Chemistry Techniques, Analytical↗

PubMed1994

Prediction and optimization of the separation of metal cations by capillary electrophoresis with indirect UV detection.

The migration of metal cations in capillary electrophoresis with indirect UV detection was investigated. A mathematical model was used to relate the electrophoretic mobility of a metal cation with two background electrolyte factors: the pH and the concentration of a complexing agent. Imidazole, which has an electrophoretic mobility close to those of metal cations, was used as the visualization agent, and 2-hydroxyisobutyric acid (HIBA) was used as the complexing agent. Through computer modeling, the electrophoretic mobilities of fourteen metal cations were predicted on the basis of five initial experiments within the factor space of pH and HIBA concentration. Good agreement was observed between the predicted electrophoretic mobilities and the observed values of the metal cations. Subsequently, the separation of a complex mixture of metal cations was successfully optimized. A complete separation of 14 metal cations including alkali, alkaline earth and transition metal(II) cations was achieved within 4 min. In addition, the effectiveness of other visualization agents and complexing agents for the separation of metal cations was examined.

Cations↗

PubMed1993

Improved chiral separation of basic compounds in capillary electrophoresis using beta-cyclodextrin and tetraalkylammonium reagents.

Approaches to improve resolution in chiral separation of several basic pharmaceutical compounds by capillary electrophoresis (CE) via a cyclodextrin (CD) inclusion complexation are described. Tetraalkylammonium reagents, including long-chain cationic surfactants and short-chain alkylammonium hydroxides, are examined for controlling the electroosmotic flow in order to improve resolution of the cationic enantiomers. In this regard, short-chain tetraalkylammonium cations (such as tetrabutylammonium and tetramethylammonium are more effective. First, the short-chain tetraalkylammonium cations can be used at much higher concentrations than the long-chain cationic surfactants, which form micelles in the few millimolar concentration range. As a result, a better capillary wall coverage is provided with the short-chain reagents, which leads to reduction or reversal of the direction of the electroosmotic flow at the acidic pH 2.5. Second, the short-chain tetraalkylammonium cations are relatively less hydrophobic and less likely to occupy the hydrophobic cavity of beta-CD than the long-chain cationic surfactants, leaving the enantioselective interaction sites more available for the analytes. The presence of these tetraalkylammonium cations was essential in many chiral separations that were reportedly not achieved by using the buffer electrolytes containing only the beta-CD as a chiral selector. In addition, a mechanism of chiral recognition by beta-CD for a group of stereoisomers is discussed.

Chemistry Techniques, Analytical↗