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 ( κ ) and C , have been developed for prediction of electrophoretic mobility difference (Δ μ ) and separation selectivity ( α ) for enantiomers in CE using dual CDs, where α and κ are defined as the ratio of μ and the ratio of binding constant ( K ) for enantiomers to each CD, respectively, C the CD concentration, and the average K for enantiomers and each CD. Experiments were carried out using dual CDs as β‐CD and dimethyl‐β‐cyclodextrin (DM‐β‐CD) and test analytes as five pairs of amphetamine drug enantiomers. A change in observed Δ μ and α 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 Δ μ and α up to the maximum value when enantiomers migrate with the same order in CD1 and CD2, and have the value of ρ  > 1.0, where ρ is the enantioselectivity ratio for CD2 to CD1, while worse Δ μ and α are obtained for enantiomers with ρ  < 1.0.