RAPID MANUAL METHOD FOR ROUTINE ASSAY OF ASCORBIC-ACID IN SERUM AND PLASMA

A method is described for the assay of ascorbic acid in either serum or heparinized plasma. The assay is based on the reduction of ferric chloride by ascorbic acid with the resulting ferrous ion quantitated by the addition of 2,4,6-tripyridyl-s-triazine (TPTZ) to form a purple color with a maximum absorbance at 595 nm. Uric acid interference is eliminated by the use of a high molarity acetate buffer and by optimising the amount of TPTZ and ferric chloride used. Protein causes rapid fading of the final color; it is therefore necessary to remove the protein by addition of 10% trichloroacetic acid to the specimen prior to the final assay. This also helps to stabilize the ascorbic acid prior to final assay. All reagents used are easily obtained and no special equipment is required.