A highly sensitive spectrophotometric method for the determination of some phenothiazine antipsychotics using Chloramine-T and indigocarmine

A new simple, accurate and precise spectrophotometric method for the determination of six phenothiazine drugs in pure form and in dosage forms is described. The method is based on the oxidation of the studied drugs by a known excess of Chloramine-T in hydrochloric acid medium and subsequent determination of the unreacted oxidant by reacting it with indigocarmine in the same acid medium. The reacted oxidant corresponds to the drug content. The colored species exhibits maximum absorption at 610 nm. The apparent molar absorptivity values and Sandell sensitivity values are in the range 1.53 x 10(4) - 2.96 x 10(4) 1 mol(-1) cm(-1) and 13.75 - 37.15 ng cm(-2), respectively. The method is highly sensitive and suitable for 1 - 15 mug ml(-1) concentrations with the detection limits being in the range, 0.0651 - 0.1724 mug ml(-1). The method was successfully applied to the studied drugs in their dosage forms. The results are reproducible within +/-1% and compare favorably with those obtained by the procedures of the British Pharmacopeia.