Separation of cationic cis-trans (Z-E) isomers and diastereoisomers using non-aqueous capillary electrophoresis

The separation of cationic cis-trans (Z-E) isomers as well as cationic diastereomers is demonstrated in non-aqueous capillary electrophoresis (NACE). No addition of surfactants, cyclodextrins or other complexing agents are necessary. Solvent mixtures of methanol and acetonitrile are used for the electrophoresis media and different electrolytes have been investigated. The separation is not dependent on differences in the pK(a) values of the substances but rather on the apparent volume of the conformers which is a result of intramolecular interactions and solvation. As long as the solutes are protonated good separation selectivity can be obtained. The separation is shown to be very much dependent on the type and concentration of the electrolyte used. The technique has been used for purity testing of drug substances. (C) 1997 Elsevier Science B.V.