Enzymatic Spectrophotometric Determination of Ascorbic Acid in Commercial Vitamin C Tablets

A spectrophotometric method for the determination of ascorbic acid contents in a variety of samples involving an enzymatic reaction and a specific blank solution is proposed. The enzyme used is ascorbate oxidase, which catalyses the oxidation of ascorbic acid to dehydroascorbic acid. Then the dehydroascorbic acid is reacted with o-phenylenediamine to produce a 2,2-anhydro quinoxaline whose absorption with respect to a specially prepared blank is observed at 358 nm. The amount of ascorbic acid present and reacted with oxygen in the presence of ascorbate oxidase was measured as the increase in the absorbance of the quinoxaline. Several commercial vitamin C tablets were analyzed using this procedure. The procedure gives satisfactory results with good selectivity and sensitivity for the determination of ascorbic acid present in these samples