The use of cyclodextrin-modified capillary electrophoresis in the determination of the enantiomeric purity.

Employing cyclodextrin-modified capillary electrophoresis, the racemates of some 30 acidic, neutral and basic dihydropyridines (DHP) were resolved using neutral and negatively charged cyclodextrins (CDs) derivatives. Whereas the enantiomers of the acidic DHPs could be separated with neutral CDs the enantiomers of the neutral DHPs were only baseline separated using the sulfobutylether substituted beta-CD. Working in reversed polarity mode--detection at the anode--improved both the peak shape and the resolution of the enantiomers. The racemates of the DHPs characterized by a secondary or tertiary amine function in the carboxylate side chain could be resolved by using either the neutral gamma-CD or negative charged CDs. The poor peak shape found with anionic CDs could be improved by addition of methanol.