The use of homocysteine in the estimation of dehydroascorbic acid

Abstract

At pH values above 6.8 homocysteine rapidly reduces dehydroascorbic acid to ascorbic acid. The ascorbic acid so formed can be estimated by reduction of indophenol dye, without any appreciable interference from the excess of homocysteine present, provided that the reaction is carried out within 30 second at pH 2.5. Based on these observations, a routine method is described for estimating dehydroascorbic acid which is more rapid and specific than other available methods. The technique involves titration with indophenol dye both before and after the reaction with homocysteine. When the presence of interfering substances is suspected, the specificity can be increased further by titration with and without the addition of boric acid. As an example of the application of the method, tests on pea cotyledons are described.