ON THE SPECIFICITY OF DYE TITRATION FOR ASCORBIC ACID

Abstract

The 2,6-dichlorophenolindophenol method of assay of vitamin C has been critically examined with respect to a number of fresh, boiled, and otherwise treated plant materials. Comparative values are given for ascorbic acid as determined by the usual method, for non-vitamin C reductants, and for dehydroascorbic acid.In the fresh uncooked materials examined, non-vitamin C reductants were not found and only in cabbage, peas, and pigweed leaves did dehydroascorbic exceed 10% of the ascorbic acid value.Boiling produced significant amounts of non-vitamin C reductant in cabbage and peas.In rose hips the dye titration gives an accurate measure of ascorbic acid. The amounts of dehydroascorbic acid and non-vitamin C reductant, even under storage at room temperature for over a year, are insignificant.It is concluded that the 2,6-dichlorophenolindophenol method of assay of vitamin C is highly specific but in the case of certain cooked foodstuffs non-vitamin C dye reductants may, without check by other methods, introduce significant errors.