Flow injection method for the assay of phenothiazine neuroleptics in pharmaceutical preparations using ammonium metavanadate

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Abstract
A simple flow injection method for the determination of chlorpromazine, promethazine, trimeprazine and perphenazine over wide ranges of concentrations is described. The method is based on the oxidation of phenothiazine with ammonium metavanadate in sulphuric acid media and subsequent measurement of the coloured, oxidized form of the product at the corresponding wavelength. A sampling rate of up to 160 h–1 was attained. Relative standard deviations for the standard samples were usually less than 0.5%. The method was applied to the determination of phenothiazines in proprietary drugs and the results were comparable to those obtained by the official methods in the British Pharmacopoeia.