Training software for chiral separations in capillary electrophoresis

Abstract

A previously published steady-state simulation program for CE was extended with a sub-menu for chiral interaction. The interaction was modelled with a hypothetical (neutral) selector with properties similar to cyclodextrins. A three-type chiral interaction model was implemented in such a way that it was valid for both anionic and cationic analytes. User-defined chiral variables in the model were: the concentration of this chiral selector, the complex formation constants (K) of both non-ionic and ionic analyte species, the relative K differences between the two optical isomers (also for both non-ionic and ionic species) and the mobility of the analyte–selector complex, relative to that of the fully dissociated free analyte. In addition the following non-chiral variables are added: the dependence of the bulk viscosity on the chiral selector concentration and the dependence of the mobilities on the viscosity. Chiral components in the data base are simulated as mixtures of optical isomers with variable enantiomeric concentration ratios. These chiral parameters, together with the original features of the program, provide a very flexible training tool for chiral separations in capillary electrophoresis. For example, determination of the optimum chiral selector concentration can be done in seconds, using the simulation software. Although the software is intended mainly for training purposes, in cases where sufficient details of existing chiral selector–analyte combinations are available, the program is also suitable for method development of chiral separations in CE.The performance of the program is illustrated with simulations, using chiral parameters obtained from literature (ibuprofen, fenoprofen, homatropine) and from our own experiments (m-fenfluramine). Simulation results were compared with experimental electropherograms.