EFFICIENCY OPTIMIZATION IN CAPILLARY ELECTROPHORETIC CHIRAL SEPARATIONS USING DYNAMIC MOBILITY MATCHING

In order to obtain high separation efficiencies in capillary electrophoresis, electromigration dispersion has to be minimized either by using very dilute samples in concentrated background electrolytes or by matching the mobilities of the analyte and the co-ion of the background electrolyte. A dynamic mobility matching method is presented here that can be used advantageously in cyclodextrin-containing zwitterionic background electrolytes. A rigorous equilibrium model has been developed to describe the effective electrophoretic mobility of the co-ion of the background electrolyte as a function of the analytical concentrations of the cyclodextrin, the zwitterionic buffer, and the hydronium ion. With adjustment of these parameters, either simultaneously or individually, the co-ion mobilities can be easily varied over a 10-fold range. Using fenoprofen as an example, predictions of the model have been verified experimentally. The separation efficiency has been maximized by varying the analytical concentration of the zwitterionic buffer while the pH and the cyclodextrin concentration of the background electrolyte were kept constant to maintain the separation selectivity. The dynamically matched mobilities resulted in symmetric enantiomer peaks and good separations.