Comparative Analysis of Imipramine Hydrochloride by UV-Spectrophotometry and Charge-Transfer Complexation

Abstract

A comparative evaluation of two spectrophotometric methods for the assay of imipramine is described. The first method, based on UV spectrophotometry was compared with a second method which is based on the molecular interaction between imipramine and chloranilic acid, to form charge-transfer complexes in which the drug acts as n-donor and chloranilic acid as a π acceptor. A complete, detailed investigation of the complex formed was made with respect to its thermodynamic parameters. Good quantitative recoveries were achieved at 255 nm via UV spectrophotometry with Beer’s law being obeyed over the concentration range of 0.98-7.85 mg % for imipramine. Meanwhile, chloranilic acid was found to form a charge-transfer complex in a 1:1 stoichiometry with maximum absorption band at 526 nm. Conformity with Beer’s law was also evident over the concentration range of 1.96-19.63 mg %. Results from the evaluated thermodynamic parameters showed that the complex was more stable at lower temperatures and possessed an enthalpy change (ΔH^o) of -2.902 Kcal. The method based on charge-transfer complexation has been successfully applied to the analysis of commercially available imipramine tablets without interference from the excipients. Both spectrophotometric methods proved adequate in the quantitative assay of the drug but charge-transfer complex formation via chloranilic acid gave better recoveries with higher reproducibility and precision, hence proved a superior method for routine laboratory assay of the drug.