Abstract
Abstract The specific determination of vitamin C consists of the following: procedure 1 oxidation of ascorbic acid (AA) to dehydroascorbic acid (DHAA) with 2,6-dichloroindophenol; reaction of DHAA with boric acid; reduction of interfering substances such as reductones (R) with homocysteine at pH 7.1; hydrazone formation from the coupling of oxidized AA, DHAA, DKGA (diketogulonic acid), and R with 2,4-dinitrophenylhydrazine (DNPH) in the presence of thiourea; color development with nitric and phosphoric acid; procedure 2 blank determination of hydrazones from DKGA and R by a modification of procedure 1 where the oxidation step is omitted and DHAA is reduced to AA before the addition of boric acid. To determine AA only, another blank (procedure 1′) is obtained by omitting the oxidation step in order to obtain hydrazone formation from substances other than AA. With whole blood, only total vitamin C could be determined because of the oxidation of AA to DHAA in the extraction procedure. With this procedure, complete recoveries of AA and DHAA added to serum and urine were obtained. Reproducibility of assays on different days was found to be satisfactory.
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