A Method for the Determination of Small Quan- Tities of Ascorbic Acid and Dehydroascorbic Acid in Turbid and Colored Solutions in the Presence of Other Reducing Substances

Most of the chemical methods which have been proposed for the estimation of ascorbic acid have been based upon the principle that, under suitable experimental conditions, ascorbic acid more or less specifically and quantitatively reduces certain colored reagents (1). The simplicity of manipulation plus the relatively close correlation between the vitamin C content of plant and animal tissues (biologically assayed) and the titration value against 2,6-dichlorophenol indophenol has led to extensive use of this reagent (2-4). Although the titration procedure has been very useful and quite satisfactory for most plant tissue and some animal tissues, there are several limitations and hazards involved in its general use. The process of titration, with usual end-point detection, is not precise for the determination of small quantities of ascorbic acid. It has been impossible to analyze extracts satisfactorily which are highly colored, such as those from beets, berries, and certain leaves. Turbid solutions lead to high end-points. The presence in most animal tissues and fluids of substances other than ascorbic acid, which slowly reduce the dye, results in high and indistinct end-points. Another important objection has been the difficulty of defining the conditions under which the extracts and reagents are most stable and the reactions quantitative. The need of frequent standardization of the dye solution is inconvenient.