Spectrophotometric determination of B-6 vitamins by coupling with diazotized P-sulfanilic acid in micellar medium of N-cetylpyridinium chloride

The water-soluble B-6 vitamins pyridoxine, pyridoxal and pyridoxamine were determined by coupling with the diazonium ion of p-sulfanilic acid, in a mi cellar medium of N-cetylpyridinium chloride (NCPC), with spectrophotometric measurement in the visible region (450 nm). A stable azo dye, with increas ed sensitivity with respect to the derivative obtained in non-micellar medi um, was rapidly formed. The addition of toxic mercury(II) acetate, recommen ded in a previous procedure to develop the colour for pyridoxine and pyrido xamine, was not required in the presence of NCPC. The procedure was applied to the determination of pyridoxine hydrochloride in commercial pharmaceuti cal preparations, with recoveries between 94 and 107% and repeatabilities b elow 1%. The differences in the coupling reaction rates of the B-6 vitamins , in the presence of boric acid and NCPC micellar medium, permitted the dif ferential-kinetic analysis of binary mixtures of the three B-6 vitamins.