Spectrophotometric determination of niclosamide using p-benzoquinone

A simple spectrophotometric method for the determination of niclosamide in pure and dosage forms has been developed. The proposed method is based on the reduction of the nitro group in niclosamide to the amino group by heating in a water bath a mixture of niclosamide solution in 95% ethanol, zinc powder and dilute hydrochloric acid for 15 minutes. The cold and clear filtrate reacts with p-benzoquinone, where a compound of pink colour is obtained which absorbs maximally at 506 nm. The stoichiometry of the proposed method and the possible pathway of the reaction is presented. The method determines from 12.5-125 mu g/ml of niclosamide with mean percentage recovery of 100.07 +/- 0.707. The suggested method was applied to Niclosan and Yomesan tablets and its validity was ascertained by standard addition technique.