A PEAK RESOLUTION MODEL FOR THE CAPILLARY ELECTROPHORETIC SEPARATION OF THE ENANTIOMERS OF WEAK ACIDS WITH HYDROXYPROPYL BETA-CYCLODEXTRIN-CONTAINING BACKGROUND ELECTROLYTES

The peak resolution equation in capillary electrophoresis (CE) has bee n extended to account for the effects of competing secondary chemical equilibria and combined with our previously developed mobility model o f chiral CE-separations. The equation explicitly accounts for the simu ltaneous effects of the pH and the resolving agent concentration of th e background electrolyte, the electroosmotic flow and the applied pote ntial. The model shows that three distinct cases can be distinguished in chiral CE separations, depending on whether only the nondissociated (type I), only the dissociated (type II), or both forms of the enanti omers (type III) complex selectively with the resolving agent. The pea k resolution surfaces are very complex, contain steep ridges, and indi cate that success of the separation depends primarily on the pH and se condarily on the concentration of the chiral resolving agent. The mode l demonstrates a unique advantage of chiral CE separations, namely, th at the migration order of the enantiomers can be reversed in-type II a nd type III separations-though not in type I separations-by selecting an appropriate combination of pH and resolving agent concentrations. N ew insights provided by the model can lead to a very pragmatic method development approach for chiral CE separations.