INDIRECT SPECTROPHOTOMETRIC DETERMINATION A THIAMINE IN PHARMACEUTICAL PREPARATIONS

An indirect, sensitive spectrophotometric method for the assay of thia mine is described, The procedure is based on the formation of a mercap tide by thiamine, with a known excess of silver ions in a buffered med ium of pH 9.0 +/- 0.1. The unreacted silver ions are determined by the formation of an ion-pair complex with 1,10-phenanthroline and 2,4,5,7 -tetrabromofluorescein, which shows an absorption maximum at 550 nm. T he absorbance is found to decrease linearly with increasing concentrat ions of thiamine, which is corroborated by the calculated correlation coefficient value of -0.998. The system obeys Beer's law for 0-25 mu g of thiamine in an overall aqueous volume of 10 ml. The molar absorpti vity and relative standard deviation (RSD) were calculated to be 7.8 x 10(4) l mol(-1) cm(-1) and 2.5% (n = 10), respectively. The proposed method was applied successfully to the determination of thiamine in ph armaceutical preparations. The reliability of the assay was establishe d by parallel determination by the standard thiochrome method and reco very studies.