Voltammetric behaviour of vitamin B1(thiamine) at a glassy carbon electrode and its determination in multivitamin tablets using anion-exchange liquid chromatography with amperometric detection under basic conditions

Abstract

Vitamin B1(thiamine) was found to give one anodic peak and three anodic peaks by cyclic voltammetry at a planar glassy carbon electrode, when treated with 0.1 mol dm–3 sodium hydroxide for 5 and 30 min, respectively. The reverse cyclic voltammograms did not show any cathodic peaks. The electro-active form of thiamine was subjected to cyclic voltammetric studies under a variety of solution conditions. The effect of pH was investigated over the range pH 7.0 to 12.5. The magnitudes of the αna values suggested that the initial oxidation reaction of thiamine involved the loss of one electron and the product of this reaction is likely to be a disulfide. The electrode reaction was found to be adsorption-controlled when only phosphate buffer was used. However, when acetonitrile was added to this supporting electrolyte at concentrations of 17.5 and 20% v/v the peak current became diffusion-controlled. A convenient and rapid method of analysis for two different multivitamin tablet formulations was developed. After a simple pre-treatment procedure, extracts were analysed using HPLC with a wall-jet amperometric detector. The results of the analyses suggest that the proposed method has promise for the routine determination of vitamin B1 in the products examined.