A simple and rapid method for the routine assay of total ascorbic acid in serum and plasma using ascorbate oxidase and o-phenylenediamine.

A simple and rapid analysis of total ascorbic acid (AsA) in serum and plasma and its automated analysis are described. AsA is oxidized by ascorbate oxidase (AsA oxidase) to dehydroascorbic acid that then reacts with o-phenylenediamine (OPDA) to form a quinoxaline derivative that absorbs at 340 nm. The change in absorbance is directly proportional to the total AsA concentration. The assay was validated with a linear concentration range of 0.8-80 mg/L, and the within-day and between-day assays precision did not exceed 8.6% and 12.5%, respectively. On 47 sera, the manual enzymatic procedure gave 0.2 mg/L on average lower values than those of an automated enzymatic procedure with a correlation coefficient of 0.847. On another 66 sera, results by automated enzymatic method correlated well with the HPLC method and the regression equation is Y (enzymatic, automated)=0.97 X (HPLC)+0.1, r=0.980, Sy.x=0.6 mg/L. An experienced analyst can perform about 24 manual assays per hour whereas the automated procedure gave a rate of 100 assays per hour.