Stability-Indicating Photochemical Method for the Assay of Thiamine by Spectrophotometry

A stability-indicating photochemical method has been developed for the assay of thiamine (TH) salts in aqueous solution and in fresh and aged vitamin preparations. It is based on the photooxidation of TH by UV irradiation to form thiochrome (TC) in alkaline solution. The TC : TH ratio under controlled conditions of light intensity, temperature, pH, exposure time, and irradiation distance is constant and can be used to determine the concentration of UV irradiated TH solutions. TC, on extraction with isobutanol from the photodegraded solution of TH, has been determined by the UV spectrophotometric method at 370 nm. It exhibits a high intensity of absorption in the UV region that can be used for the assay of even low concentrations of TH. Under optimum conditions, Beer’s law is obeyed in the concentration range of 0.20–2.00 mg/100 ml (R2 = 09998). The limit of detection (LOD) and limit of quantification (LOQ) are 0.0076 and 0.0231 mg/100 ml, respectively. The method has been validated and applied to aqueous solutions and vitamin preparations. The results have statistically been compared with the United States Pharmacopeia liquid chromatography method. It has been found that there is no significant difference between the two methods at 95% confidence level.