Abstract

A rapid and sensitive spectrophotometric method has been developed for the determination of two antihistamines, mebrophenhydramine hydrochloride and hydroxyzine hydrochloride in pure form and in different dosage forms. The method is based on the formation of stable donor-acceptor complex between the studied antihistamines and chloranilic acid in acetonitrile. The resulting intensely coloured purple chloranilic acid radical anion possesses a characteristic maximum at ' 535 nm. Beer's law is obeyed over the concentration range 25-150 μg/ml in respect of both drugs. The stoichiometric ratio and stability constant of each charge-transfer complex are determined and the mechanism of the reaction is discussed. The molar absorptivity and Sandell sensitivity of the charge-transfer complexes formed are reported. Statistical treatment of the experimental results indicates that the method is precise and accurate. Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedure. The procedure described was successfully applied to the determination of the bulk drugs and their pharmaceutical formulations.