An improved method for determination of L-ascorbic acid and L-dehydroascorbic acid in blood plasma.

Various conditions for reducing L-dehydroascorbic acid were studied, using dithiothreitol. This led to an improved method for the separate determination of L-ascorbic acid and L-dehydroascorbic acid in blood plasma. The content of ascorbic acid was determined by an alpha,alpha'-dipyridyl method (A). Dehydroascorbic acid was reduced to ascorbic acid by incubation with dithiothreitol at room temperature for 10 min at pH 6.5 to 8.0. After removing the excess dithiothreitol with N-ethylmaleimide, total ascorbic acids, i.e. reduced plus original, were determined by the alpha,alpha'-dipyridyl method (B). The amount of dehydroascorbic acid could then be calculated from these results (B minus A).