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 presented. The charged resolving agent migration model (CHARM model) is based on the consideration of the simultaneous protonation and 1:1-type complexation 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-electrolytes, strong electrolytes and weak electrolytes. Analysis of the resulting surfaces as a function of the pH and the charged cyclodextrin concentration of the background electrolyte indicates that in the absence of electroosmotic flow (e.g. in neutral-coated capillaries), only two series of measurements have to be carried out to locate the best separation 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 taking advantage of the predictions of the CHARM model, the utility of a large number of char ed cyclodextrins, each offering different intermolecular (enantioselective) interactions can be evaluated in a short period of time for any chiral analyte. (C) 1997 Elsevier Science B.V.