Metaphosphoric Acid in the Extraction and Titration of Vitamin C*

Of the many methods that have been proposed for the direct chemical determination of vitamin C in plant. and animal tissues, those based upon the reduction of 2 ,Bdichlorophenol indophenol have been adopted far more widely than others. The original indophenol procedure proposed by Tillmans and associates (1) a short time before the vitamin was isolated and identified (2) was soon modified in varying degrees in a number of laboratories (3-6). The indophenol method depends upon the fact, that vitamin C is the major or only natural tissue component which reduces the dye rapidly in an acid solution (e.g. pH 2 to 4). The present, paper deals primarily with the value of having metaphosphoric acid in the acetic acid or trichloroacetic acid used for extracting and titrating the vitamin. In general we have found the procedure outlined by Bessey and King (5) more satisfactory than other methods which have been proposed for tissue analysis, and many other laboratories appear to have had essentially the same experience. The first suggestion of using metaphosphoric acid which came to our attention was in the paper by Fujita and Iwatake (7).