CAPILLARY ELECTROPHORETIC CHIRAL SEPARATIONS WITH CYCLODEXTRIN ADDITIVES .1. ACIDS - CHIRAL SELECTIVITY AS A FUNCTION OF PH AND THE CONCENTRATION OF BETA-CYCLODEXTRIN FOR FENOPROFEN AND IBUPROFEN

An equilibrium model has been developed to describe the pH and cyclodextrin concentration dependence of the electrophoretic mobilities as well as the chiral selectivities observed during the capillary electrophoretic separation of the enantiomers of weak acids. The parameters of the model can be readily derived from three specific sets of capillary electrophoretic experiments: cyclodextrin-free background electrolytes of varying pH values are used in the first set of experiments, background electrolytes with the same high pH but varying concentrations of cyclodextrin are used in the second set, and background electrolytes of the same low pH but with varying concentrations of cyclodextrin are used in the third set of experiments. The model has been tested with fenoprofen and ibuprofen as model substances and beta-cyclodextrin as resolving agent, and an excellent agreement has been found between the calculated and the measured values. Baseline separations have been achieved for the enantiomers of both fenoprofen and ibuprofen in less than thirty minutes.