Simultaneous spectrophotometric determination of chlorpromazine, perphenazine and acetopromazine by use of the kinetic wavelength pair-method

The potential of the kinetic wavelength-pair method for resolution of ternary mixtures of analytes that show strong kinetic and spectral overlap was evaluated. The oxidative coupling reactions between 3-methylbenzothiazolin-2-one hydrazone (MBTH) and chlorpromazine, perphenazine and acetopromazine, using Fe(III) as oxidant, were used with this purpose. These systems were good candidates for this evaluation since spectra of reaction products, specially those from chlorpromazine and perphenazine were strongly overlapped, and on the other hand, the relative rate constants for the reactions of acetopromazine, perphenazine and chlorpromazine with MBTH were 1 : 1.06 : 1.36. Selectivity in the resolution was achieved by measuring the initial rate difference at the wavelength pairs 770-610 nm and 788-628 nm where the contribution of acetopromazine was minimal and maximal, respectively. The three phenothiazines studied were simultaneously determined at concentrations from 2 to 5 μg/ml, with relative errors less than 7% in most instances. The proposed method was applied to the determination of perphenazine and acetopromazine in human serum with analytical recoveries ranging between 89 and 112%.