Capillary electrophoresis chiral separations of basic compounds using cationic cyclodextrin.

Abstract

Chiral separations of basic enantiomers were carried out by using a cationic cyclodextrin (CD), quaternary ammonium beta-cyclodextrin (QA-beta-CD), under counter-electroosmotic flow (counter-EOF) conditions. The special characteristics of using a cationic CD to separate cationic enantiomers is that the EOF can be reversed and the analyte-CD complexation is reduced. This is especially useful for chiral separation of cationic compounds, which strongly bind with neutral and anionic CDs (such as tricyclic amine compounds). The reduction in the binding constants between the CD and the cationic enantiomers makes it easier to control the optimum CD concentration. The application of the cationic CD also eliminated the peak tailing problem caused by electrodispersion. The effect of pH and the concentration of QA-betaCD on chiral separation has been studied. At pH 3.02, no separation for any of the enantiomeric amines was observed. At pH 8.20, chiral separation of some tricyclic compounds was achieved at very high resolution due to the counter-EOF setup. At pH 11.6, most enantiomers were neutral and chiral separation of some bicyclic compounds can be obtained.