Simultaneous two- and three-component determinations in multicomponent mixtures by extraction-spectrophotometry and thermochromism of ion-association complexes

Abstract

A selective method of determination of amines and quaternary ammonium salts by solvent extraction and thermochromism of ion-association complexes has been established. The method is based on the formation of ion-association species with tetrabromophenolphthalein ethyl ester and the thermochromism effect in the organic phase at low temperature. The absorbance of the red amine charge-transfer complexes decreases quantitatively (Δ A) with increase in temperature (Δ T), and Δ A Δ T is characteristic of a particular species. This characteristic has been applied for the sensitive and selective determination of amines. The absorbance of the blue quaternary ammonium ion-association complexes does not vary with temperature, however, and the quaternary ammonium compounds can be determined without interference by amines because of the disappearance of the red species at 60°. Methylephedrine, diphenhydramine, ephedrine (amines), benzethonium and/or berberine (quaternary ammonium compounds) in two- and three-component mixtures can be determined by using the thermochromism effect. The method is highly selective, sensitive and reproducible.