Epimeric separation of L-ascorbic acid and D-isoascorbic acid by capillaryzone electrophoresis

Capillary zone electrophoresis (CZE) was used for separation of L-ascorbic acid (L-AA) and D-isoascorbic acid (D-IAA) in a model system. The effects o f borate buffer concentration (0.05-0.25 M) and pH (pH 7.5-9.0) on migratio n time, resolution (Rs), and theoretical plates (N) were investigated. The migration times of L-AA and D-IAA increased with the increasing pH of carri er electrolyte (0.2 berate buffer), and the resolutions (Rs) of L-AA and D- IAA were calculated to be 12.98 at pH 9.0. Concentrations of berate buffer (pH 9.0) increased the Rs values of L-AA and D-IAA, and buffer concentratio ns >0.1 M were found to be effective for separation of L-AA and D-IAA. Meth anol in the carrier electrolyte was also influential in improving the separ ation of L-AA and D-IAA, which increased with the increasing concentrations (0-10%) of methanol. The optimal separation conditions for L-AA and D-IAA were as follows: carrier electrolyte, 0.2 M berate buffer (pH 9.0); applied voltage, 25 kV, with an uncoated fused silica capillary, 75 mu m (i.d.) x 57 cm.