Simultaneous spectrophotometric determination of dibucaine and chlorpheniramine maleate in pharmaceuticals using thermochromism of ion associates

Abstract

A spectrophotometric method has been developed for the determination of basic drugs in pharmaceutical preparations. The method is based on solvent extraction and utilisation of thermochromism of red ion associates with tetrabromophenolphthalein ethyl ester (TBPE). The maximum absorbance of the dibucaine-TBPE associate occurred at 555 nm and that of the chlorpheniramine associate at 575 nm. The absorbance of the red species decreased quantitatively with temperature increase and the value of the absorbance change with temperature change (ΔA/Δt) was characteristic for each amine associate. The thermochromism phenomenon was applied to the simultaneous determination of two amines, dibucaine and chlorpheniramine maleate. The reproducibility was good. This method is highly selective, sensitive (apparent molar absorptivities for amines 2 × 10⁴–4.1 × 10⁴ l mol^–1 cm^–1) and precise for the determination of bulky drugs in multi-component samples.