Spectrofluorometric assay of thiamine hydrochloride in injections and multivitamin preparations

A spectrofluorometric method is described for the determination of thiamine hydrochloride. The method is based on formation of a fluorescent product by oxidation of thiamine HCl with 2,3,5,6-tetrabromo-1,4-benzoquinone in aqueous acetonitrile solution. The reaction product is stable for at least 6 h and shows excitation and emission maxima around 355 and 420 nm, respectively. The method is highly selective for thiamine HCl in the presence of other B vitamins. Thiamine HCl can be determined at concentrations as low as 20-160 ng/mL of the final solutions. When the method was applied to the determination of thiamine HCl added to some commercially available multivitamin preparations, recoveries were 98.78-99.98%.