Determination of low levels of phenothiazine sulphoxides in phenothiazine drug substances and formulations by thin-layer chromatography-second-derivative spectrofluorimetry.

A thin-layer chromatographic-second derivative spectrofluorimetric procedure has been developed for low levels of sulphoxide (down to 0.01%, w/w) in phenothiazine drug substances and formulations. The method has been applied to prochlorperazine maleate, chlorpromazine hydrochloride and promethazine hydrochloride. It has also been applied to pharmaceutical formulations of promethazine hydrochloride and comparison of the results with those obtained by a published difference spectrophotometric procedure for promethazine sulphoxide showed that there was good agreement. The method is simple, rapid, accurate and precise and seems to have general application to the determination of low levels of sulphoxide in phenothiazine drug substances or formulations.