Rapid Method for Determination of Ascorbic Acid in Urine

OE AND KUETHEE (1) determined ascorbic acid in biologic media by oxidizing ascorbic acid to dehydroascorbic acid, using norit in the presence of trichloroacetic acid. This compound was incubated with 2,4-dinitrophenylhydrazine in the presence of thiourea for 3 hr. at 37#{176}to form an osazone, which was then treated with 85 % sulfuric acid, and the resulting color was read in a photoelectric colorimeter using a 540 mIt filter. Since then a number of investigators (2-7) have published modifi-cations of this procedure by changing the original acid medium, the oxidizing agent, and/or the final acid medium used for color develop-ment. Schaffert and Kingsley (8) modified the original procedure by the use of incubation at 100#{176}for 10 mm. Schwartz and Williams (9) determined ascorbic acid and dehydroascorbic acid simultaneously by varying the addition sequence of the reagents used in the oxida-tion step, i.e., the 2,6-dichiorophenolindophenol (DCPP) and the thiourea. For color development they used a mixture of phosphoric and hydrochloric acids. Their method was sensitive, and the recovery of known amounts of ascorbic acid was very close to the theoretic values, but the 3-hr. incubation at 37#{176}was still used. This paper describes a method that eliminates the norit treatment and shortens the incubation time from 3 hr. to 10 mm