ASSAY FOR BOTH ASCORBIC AND DEHYDROASCORBIC ACID IN DAIRY FOODS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING PRECOLUMN DERIVATIZATION WITH METHOXY-1,2-PHENYLENEDIAMINE AND ETHOXY-1,2-PHENYLENEDIAMINE

A procedure for the simultaneous determination of both ascorbic and dehydroascorbic acid in dairy foods by high-performance liquid chromatography using precolumn derivatization with 4-methoxy- and 4-ethoxy-1,2-phenylenediamine is presented. The derivatives are isolated by solid-phase extraction and analysed by fluorescence detection on a resin-type reversed-phase column at pH 9. Retention times are 2 and 3.2 min for the derivatives of ascorbic and dehydroascorbic acid, respectively. Relative standard deviations of the within- and between-assay tests are 7.1 and 5.5%, respectively, for ascorbic and 11 and 9%, respectively, dehydroascorbic acid. The limits of detection are 50 and 70 fmol per 5-mu-l injection for ascorbic and dehydroascorbic acid, respectively.