QUANTITATION OF ASCORBIC-ACID BY LIQUID-CHROMATOGRAPHY WITH COULOMETRIC ELECTROCHEMICAL DETECTION

The determination of total vitamin C has been challenging because the oxidized molecule, dehydroascorbic acid, is unstable under most conditions and is not readily quantitated by absorbance detectors or by electrochemical detectors. In the present work a method for quantitation of ascorbic acid is described and a procedure that allows for essentially complete reduction of dehydroascorbic acid and quantitation by coulometric electrochemical detection is presented. Evaluations are provided of the time necessary for conversion of dehydroascorbic acid to ascorbic acid, the pH optimum of the reduction process and the required ratio of the reductant used (beta-mercaptoethanol) to the sample content of dehydroascorbic acid.