Chiral separation in capillary electrophoresis using dual neutral cyclodextrins: Theoretical models of electrophoretic mobility difference and separation selectivity

Simple equations and theoretical models, related to enantioselectivity (kappa) and KC, have been developed for prediction of electrophoretic mobility difference (Delta mu) and separation selectivity (alpha) for enantiomers in CE using dual CDs, where alpha and kappa are defined as the ratio of mu and the ratio of binding constant (K) for enantiomers to each CD, C the CD concentration, and K the average K for enantiomers and each respectively, CD. Experiments were carried out using dual CDs as beta-CD and dimethyl-beta-cyclodextrin (DM-beta-CD) and test analytes as five pairs of amphetamine drug enantiomers. A change in observed Delta mu and alpha of enantiomers in dual CDs was found to be in excellent agreement with the theoretical models. For example, in comparison with single CD1, dual CDs can enhance Delta mu and alpha up to the maximum value when enantiomers migrate with the same order in CD1 and CD2, and have the value of rho > 1.0, where rho is the enantioselectivity ratio for CD2 to CD1, while worse Delta mu and alpha are obtained for enantiomers with rho < 1.0.