Rapid spectrophotometric assay of phenothiazine drugs in pharmaceutical preparations
A simple, accurate and rapid method for the quantitative determination of ten phenothiazine drugs in either the pure form or in pharmaceutical formulations is proposed. The method is based on the development of pink or violet products with N-bromosuccinimide in a strong sulphuric acid medium. The reaction is suggested to proceed via oxidation of the phenothiazine nucleus into a semiquinonoid radica. The wavelengths of maximum absorption range from 512 to 565 nm. Molar absorptivities range from 6 × 103 to 20 × 103 l mol–1 cm–1. A linear correlation was found between absorbance (at the λmax.) and concentration. The resulting colours are well developed within 20–30 min and are stable for at least 10 h. Results of analyses of pure drugs and their dosage forms by the proposed method are in good agreement with those of the official BP 1980 and USP XX procedures.