The determination of vitamin C in normal human plasma and erythrocytes.

Abstract 1. 1. Various methods based on (a) reduction of indophenol, (b) formation of a derivative with 2: 4-dinitrophenylhydrazine, and designed to measure ascorbic acid, dehydroascorbic acid and diketogulonic acid have been applied to the analysis of normal human plasma and erythrocytes. 2. 2. It is concluded that measurement of indophenol reduction at pH ca . 4 in protein-free filtrates of plasma, or of carbon monoxide saturated erythrocytes, treated with p -chloromercuribenzoic acid provides the most accurate means of determining ascorbic acid in these materials. 3. 3. Comparison of values for total vitamin C and ascorbic acid of human plasma indicates that the amount of dehydroascorbic acid and/or diketogulonic acid in normal plasma is smaller than can be reliably determined by this procedure. The similar, and contrary, findings of others have been discussed in relation to the methods used. 4. 4. In erythrocytes the results obtained were consistent with the presence of a small amount of dehydroascorbic acid and/or diketogulonic acid. 5. 5. Measurement of indophenol reduction of plasma or erythrocyte filtrates treated with hydrogen sulphide gives results which are believed to include some non-ascorbic acid material and thus to overestimate any dehydroascorbic acid present. 6. 6. The concentration of total vitamin C in plasma is higher than that in erythrocytes, freed as far as possible from leucocytes, when the concentration in plasma is high. When the concentration in plasma is low the reverse relationship holds. In contrast, the concentration of ascorbic acid in plasma tends to be higher than that in erythrocytes at all levels.