ENHANCED SPECTROPHOTOMETRIC DETERMINATION OF NICOTINIC-ACID IN A SODIUM DODECYL-SULFATE MICELLAR MEDIUM

The spectrophotometric determination of pyridine and pyridine derivati ves by means of the Konig reaction was studied in micellar media of so dium dodecyl sulphate (SDS), N-cetylpyridinium chloride and Triton X-1 00. The sensitivity was largely increased in SDS micellar medium. The attack of the pyridine ring with cyanogen bromide to produce a glutaco nic aldehyde was not affected by the presence of SDS, but the yield of the coupling reaction with an arylamine to produce a polymethine dye was largely increased. In the SDS micellar medium, aniline was superio r to other coupling reagents. The limits of detection (LODs) were 6 x 10(-7), 1 x 10(-6) and 5 x 10(-7) M for pyridine, pyrrol-ylmethylpyrid ine and nicotinic acid, respectively, and the reproducibility for 2 x 10(-5) M solutions was ca. 2%. In the absence of SDS, the LODs were 3 x 10(-6), 3 x 10(-6) and 9 x 10(-6) M, respectively, and the reproduci bility was ca. 3.5%. Application was made to the determination of nico tinic acid in pharmaceuticals.