Determination of ascorbic acid and isoascorbic acid by capillary zone electrophoresis: application to fruit juices and to a pharmaceutical formulation.

Capillary zone electrophoresis was applied to the determination of ascorbic and isoascorbic acid, analysing the various parameters of influence such as the separation voltage, the buffer pH and concentration, the type of separation capillary or the loading conditions. Both analytes could be adequately determined within 5 min. The proposed method uses a 20 cm x 25 microns i.d. coated column, 0.1 M phosphate buffer pH 5.0, 8 kV separation voltage and light absorption detection at 265 nm. Linear calibration curves were obtained in the 0-1 mg mi-1 range, with detection limits of 0.5 micrograms ml-1. This method proved to be very rapid, simple and practical for the qualitative and quantitative determination of ascorbic acid in lemon and orange juices, as well as in a commercially available pharmaceutical formulation.