Use of extractive spectrophotometry and ion-pair formation with chromeazurol S for the assay of some phenothiazine antipsychotic drugs in pharmaceutical formulations

A simple, rapid and fairly sensitive extractive spectrophotometric method is described for the assay of six phenothiazine antipsychotic drugs in pure form and in their pharmaceutical formulations. The method is based on the ion-pair complex formation between the drugs and the acid dye, chromeazurol S in buffer medium of pH 1.09. The chromogen, being extractable with chloroform, could be measured quantitatively at 460 nm. All variables were studied to optimize the reaction conditions. The method obeys Beer's law and the precision and accuracy of the method were checked by the British Pharmacopoeial procedures. The detection limit is 1 or 2 mu g ml(-1) and the molar absorptivity is in the range, 1.07 x 10(4)-2.12 x 10(4) l mol(-1) cm(-1).