Successive determination of thiamine and ascorbic acid in pharmaceuticals by flow injection analysis

A simple and rapid fluorimetric method for the determination of mixtures of thiamine and ascorbic acid is proposed. The procedure is based on the oxidation with mercury(II) of the B1 and C vitamins to form thiochrome (TC) and quinoxaline derivate, respectively. Both reaction products exhibit fluorescence at the same wavelengths (lambdaex = 356 and lambdaem = 440 nm). The procedure is optimised in a flow injection (FI) system and applied with excellent results in the determination of B1 and C vitamins in commercial pharmaceutical preparations. The calibration graphs were linear over the range 2-100 microg ml(-1) for thiamine and 5-100 microg ml(-1) for ascorbic acid. The throughput was 25 samples per hour.