DRY LOOK AT THE CHARM (CHARGED RESOLVING AGENT MIGRATION) MODEL OF ENANTIOMER SEPARATIONS BY CAPILLARY ELECTROPHORESIS

An analysis of the capillary electrophoretic separation of enantiomers using permanently charged cyclodextrins as resolving agents is presen ted. The charged resolving agent migration model (CHARM model) is base d on the consideration of the simultaneous protonation and 1:1-type co mplexation equilibria that take place in such background electrolytes. Analytical expressions are derived that allow the calculation of the effective charge, effective mobility, separation selectivity and peak resolution values for various enantiomeric analyte classes: non-electr olytes, strong electrolytes and weak electrolytes. Analysis of the res ulting surfaces as a function of the pH and the charged cyclodextrin c oncentration of the background electrolyte indicates that in the absen ce of electroosmotic flow (e.g. in neutral-coated capillaries), only t wo series of measurements have to be carried out to locate the best se paration conditions as a function of the concentration of the charged cyclodextrin: one in low-pH background electrolytes (e.g. pH 2.2) and one in high-pH background electrolytes (e.g. pH 9.5 or above). By taki ng advantage of the predictions of the CHARM model, the utility of a l arge number of char ed cyclodextrins, each offering different intermol ecular (enantioselective) interactions can be evaluated in a short per iod of time for any chiral analyte. (C) 1997 Elsevier Science B.V.