Enantiomeric sepration capillary electrophoresis usimh dual cyclodextrins

Abstract

In initial work, enantiomeric separation in capillary electrophoresis (CE) was carried out using a chiral selector as single cyclodextrin (CD), β- or DM-β-CD, in a pH 3.0 triethanolammonium-phosphate buffer and test analytes as enantiomers of amphetamine drugs such as amphetamine, methamphetamine, ephedrine, pseudoephedrine and norephedrine. The binding constant (K) for each isomer to CD was determined, by fitting electrophoretic mobility (µ) of the analyte as a function of CD concentration (C). Simple equations and theoretical models of ∆µ, based on enantioselectivity (α) and (KC-bar), have been developed for prediction and explanation of a change in ∆µ of enantiomers in a wide range of dual CDs concentrations, where α is the ratio of K for enantiomers, and (K-bar) the average K for enantiomers. In dual CDs system, an increase or a decrease in observed ∆µ was found to be in good agreement with prediction according to the theoretical models of ∆µ. For example, in comparison with single CD1, dual CDs can enhance ∆µ when enantiomers have α for CD2 greater than that for CD1. In either single or dual CDs system, over a wide range of CD concentrations, good agreement was found for observed and predicted values of ∆µ, while the observed slightly less than predicted values of resolution were obtained when two major contributions, diffusion and electromigration, dispersion, were taken into account for prediction of peak variance and efficiency. In comparison with single CD, dual CDs was found to improve resolution of some enantiomers and to obtain achieved baseline resolution of all test analytes.