Selective determination of thiamine (vitamin B 1) in pharmaceutical preparations by direct potentiometric argentometric titration with use of the silver—silver sulphide ion-selective electrode

Abstract

A simple and selective argentometric titration method is described for determination of thiamine (vitamin B 1), based on direct potentiometric titration in alkaline media (⩾0.5 M) in which a chemical transformation takes place, creating two acidic groups, the protons of which are replaceable by silver ions. The acidimetric and argentometric potentiometric titration curves display two consecutive potential breaks specific for thiamine. The second break is reproducible and corresponds to a 2:1 reaction ratio of silver to thiamine. No interference is caused by other vitamins, active ingredients and inactive excipients normally present in multivitamin preparations. The results obtained for determination of thiamine in pure powders, pharmaceutical tablets and ampoules showed an average recovery of 98.2% of the nominal values and a mean standard deviation of 0.5%, and agreed fairly well with data obtained by the British Pharmacopoeia procedure.