Determination of small quantities of nicotinic acid in presence of nicotinamide by modified Konig reaction

Abstract

A modified sensitive spectrophotometric method for the determination of nicotinic acid and nicotinamide in sub-microgram levels is described. During their reaction with cynogen bromide, the pyridine rings are split by the Konig reaction and the reaction products are coupled with diazotised, <i>p</i>-aminoacetophenone, <i>p-</i>aminobenzoic acid, sulphanilic acid and H-acid to form coloured azo dyes. The colour system obeys Beer’s law over the concentration range of 0.008-0.08 ppm, 0.02 -0. 16 ppm, 0.04-0.36 ppm and 0.05-0.4 ppm for nicotinic acid respectively. Similarly, the colour system obeys Beer’s law over the concentration range of 0. 02- 0.2 ppm. 0.04-0.4 ppm, 0.05 -0.56<i> </i>ppm and 0.07-0.6 ppm for nicotinamide using PAA P, PABA, sulphanilic acid and H-acid respectively. <i>p</i>-Aminoacetophenone gives the best result for the determination of nicotinic acid/ nicotinamide. The sensitivity of the method after this modification is found to be about eight times more than that of the conventional Konig reaction . The method is free from interference of common diverse ion and has been satisfactorily applied to the determination of nicotinic acid in presence of nicotinamide in food, blood, urine and pharmaceuticals.