Use of thermochromism of associates for the determination of antihistamine drugs in pharmaceutical preparations and urine

Abstract

A sensitive and selective spectrophotometric method has been developed for the assay of diphenhydramine and chlorpheniramine maleate in pharmaceutical preparations and urine. The method depends on ion-pair extraction and thermochromism of associates formed between tertiary amines and tetrabromophenolphthalein ethyl ester (TBPE). The method obeys Beer's law in the concentration range 1 × 10^–6–5 × 10^–6M(0.2918–1.459 µg ml^–1) of diphenhydramine and 1 × 10^–6–5 × 10^–6M(0.391–1.950 µg ml^–1) of chlorpheniramine maleate. The proposed method can be applied to the determination of diphenhydramine and chlorpheniramine maleate with quaternary ammonium salts in pharmaceuticals of the ointment and liquid types and chlorpheniramine maleate in urine. Thermochromism of associates with amines was also investigated.