A chemical method of estimation of nicotinic acid in urine in the presence of sugar.

It has been reported that intravenous injection of nicotinic acid produces hypoglycemia in normal humans (l-4). A definite improvement in the carbohydrate tolerance of diabetic patients after administration of nicotinic acid has also been reported (4). It was therefore of interest to study the urinary excretion of nicotinic acid in diabetic patients. In the chemical estimation of nicotinic acid in urine by Kiinig’s reaction (5) the urine is first digested either with acid (6) or with alkali (7) in a water bath to convert derivatives of nicotinic acid excreted in the urine to nicotinic acid. The color of the urine after digestion interferes with the estimation of nicotinic acid and different workers tried to remove the color by different methods. While Melnick and Field (6) and Swaminathan (7) used charcoal to remove the interfering pigments, Perlzweig, Levy, and Sarett (8) and Dann and Handler (9) employed Lloyd’s reagent. Wang and Kodicek (lo), on the other hand, treated the digested urine first with isobutanol, which removed some of the colors, and the remaining pigments were subsequently oxidized with potassium permanganate. R,ecently Swaminathan used zinc hydroxide to remove the color (11). The urine of diabetic patients, however, after digestion with acid or alkali gave a highly colored extract. The int.erfering color could not be removed by any of the methods so far used (6-11). It seemed that most of the color produced after digestion was due to charring of the sugar present in the urine. In the present paper a method for the estimation of nicotinic acid in the urine containing sugar has been described.