Résumé
Aqueous cyanocobalamin solutions [pH 1-7] have been photolysed in the presence of individual B [thiamine HCl, riboflavin, nicotinamide and pyridoxine HCl] and C [ascorbic acid] vitamins with visible light. The degraded solutions were subjected to thin-layer chromatography using several solvent systems and the Rf values of the vitamins and their photoproducts were determined. The major photoproducts have been identified by comparison of their Rf values with those of the authentic compounds. Cyanocobalamin leads to the formation of hydroxocobalamin. Thiamine HCl gives rise to 4-methyl-5-[C-hydroxyethyl] thiazole and 2-methyl-4-amino-5-hydroxymethyl-pyrimidine in trace amounts whereas riboflavin degrades extensively to formylmethylflavin and lumichrome, and to a smaller extent to lumiflavin and carboxymethylflavin. Ascorbic acid is oxidized to dehydroascorbic acid. Nicotinamide and pyridoxine HCl do not undergo any degradation. The extent of degradation depends upon the pH