Spectrophotometric determination of ascorbic acid and thiamine hydrochloride in pharmaceutical products using derivative spectrophotometry

Abstract

Direct spectrophotometric methods for the determination of ascorbic acid (vitamin C) and thiamine hydrochloride (vitamin B₁) each in the presence of its degradation product are presented. The methods are based on the use of UV derivative spectrophotometric measurements—the first derivative at 215 nm for ascorbic acid and the second derivative at 254 nm for thiamine hydrochloride. The values obtained are linearly related to the concentration of each vitamin solution and have relative standard deviations of 0.52 and 1.07%, respectively. The mean percentage recoveries for mixtures of each vitamin with their respective degradation product were found to be 101.5 and 99.4%, respectively. Graphs of log C(%m/V)versus time for ascorbic acid solution in 3 N hydrochloric acid and for thiamine hydrochloride solution in buffer at pH 10 were straight lines with slopes of –0.1044 d^–1 and –0.0207 h^–1, respectively. The methods have been successfully applied to monitor the stability of the vitamins.