A simple, rapid and sensitive spectrophotometric method was described for the quant. detn. of 6 phenothiazine-based antipsychotic and anticholinergic drugs in bulk and in formulations. The method is based on the formation of stable phenothiazinium free radical cation by the use of sodium nitroprusside as the chromogenic agent. The drugs in a 1.5-2.5M H2SO4 medium reacted with the reagent to give intense orange or purple products which had characteristic absorption maxima at 500-530 nm. Beer's law was obeyed over the concn. range 4-32 I¼g/mL with apparent molar absorptivities ranging from 9.8 A— 103 16.59 A— 103 l.mol.-1 cm-1. The av. percent recovery was 99.5-101.6. The accuracy and precision of the assay method were comparable to those of the British Pharmacopeia method. [on SciFinder(R)]
