Determination of phenothiazines by charge-transfer complex formation with chloranilic acid.

A rapid and sensitive spectrophotometrc method has been developed for the microdetermination of some phenothiazine derivatives as the pure substances and in different dosage forms. The method depends on the formation of stable donor-acceptor complexes between phenothiazines and chloranilic acid in an acetonitrile-2-propanol solvent mixture. The resulting intensely purple chloranilic acid radical anion possesses a characteristic absorption maximum at 515 nm. Beer's law is obeyed over the concentration ranges 1-6, 1-10 and 5-30 mug ml for prochlorperazine dimaleate, trifluoperazine dihydrochloride and thiethylperazine dihydrochloride, with apparent molar absorptivities of 7.76 x 10(4), 1.95 x 10(4) and 6.64 x 10(3) 1. mole(-1).cm(-1), respectively. Statistical comparison of the results with those of an official method shows excellent agreement and indicates no significant difference in precision.