A colorimetric method for the determination of the principal metabolites of nicotinic acid in human urine

Abstract

Since the main metabolites of nicotinic acid normally excreted in human urine are acid amides, the possibility was investigated of developing a colorimetric method for their detn. in urine, based on conversion of the carbonamide into an amino group by heating with hypobromite, followed by diazotization and coupling of the amino compound formed to yield an azo dye. When the excess of hypobromite was suitably controlled, and N-(1-naphthyl)-ethylenediamine dihydrochloride was used as coupling agent, azo colors could be produced from N-methyl-2-pyridone-5-carbonamide, N-methyl-2-pyridone-3-carbonamide, N-methylnicotinamide and nicotinamide. Opt. conditions for color production were ascertained and a method worked out for detn. of amts. of from 1 to 50 ug. of each of the color-producing substances. The removal from urine of substances which interfere with the color reaction was investigated, and procedures are descr. which were suitable for the detn. of N-methyl-1-pyridone-5-carbonamide and N-methylnicoti-amide in human urine. Using the present methods, the urinary excretions of nicotinic acid metabolites by 3 adult subjects were detd. before and after admn. of quinolinic acid. The results showed evidence of no more than a slight conversion of quinolinic into nicotinic acid.