QUANTITATION OF DEHYDROASCORBIC ACID BY THE KINETIC MEASUREMENT OF A DERIVATIZATION REACTION

Micromolar concentrations of dehydroascorbic acid in aqueous solutions react with methanol-containing phosphate or citrate buffers to form a mixture of derivatives with an absorption maximum at 346 nm. The compounds, different methyl ketals, were analyzed using fast atom bombardment mass spectrometry. After calibration, kinetic analysis of the formation rates can be used for fast and simple determination of dehydroascorbic acid concentrations. In samples containing both forms of vitamin C, ascorbate and dehydroascorbic acid, autoxidation of ascorbate can be inhibited by addition of transition metal complexing agents; thus, only formation rates accounting for the amounts of dehydroascorbic acid are measured.