Abstract

An extractive spectrophotometric method for the determination of promethazine Hydeochloride in either pure form or in pharmaceutical formulations is described. The method is based on the formation of a red coloured product with sulphanilamide in the presence of N-bromosuccinimide. The reaction presumably proceeds via preliminary oxidation of the phenothiazine nucleus to a phenothiazinyl radical followed by coupling of the sulphanilamide in C-3 or C-7 position. The chromogen produced is stable for more than 3 days at room temperature. Beer's law is obeyed in the range of concentration of 5-25 mg/ml at the maximum absorption of 510 nm. Optimum analytical conditions were determined. Analytical data for determination of the pure compound is presented together with the application of the proposed method to the analysis of some pharmaceutical preparations. The results compare favourably with those of official methods. Furthermore, the method is specific for C-2 unsubstiuted promethazine hydrochloride.