A simple and sensitive analytical method for the determination of thiamine in pharmaceutical preparations

A simple and sensitive method for spectrophotometric determination of thiamine with leucocrystal violet was elaborated. Spectrophotometric quantification based on the following reaction sequence: thiamine was oxidized with potassium iodate(V) to the colourless product and a stoichiometric amount of iodide ions was formed. The latter reacted with the excess of iodate(V) ions in acidic medium, to form free iodine which oxidized leucocrystal violet to the crystal violet dye. The absorbance of the crystal violet dye formed was measured at pH 4.1 +/- 0.1 and 589 nm. The measured absorbance obeyed Beer's law over the thiamine concentration range 0.4-2.4 mu g/mL. The linear regression coefficients were a = 0.3339, b = -0.0001, and r = 0.9998 (for the general form of the linear equation y = ax + b). The apparent molar absorptivity of the coloured compound was 1.12 x 10(5) L/mol cm for thiamine. The limit of detection and limit of thiamine determination were found to be 0.19 and 0.26 mu g/mL, respectively. Optimum reaction conditions providing maximum and constant absorbance were optimized. The procedure was successfully used to the determination of vitamine B-1 in pharmaceutical formulations. The obtained results were compared with those obtained by the method proposed by Polish Standard.