Author(s): Alwarthan AA, Fattah SA, Zahran NM
Cephalexin in pure form and in dosage form was assayed colorimetrically in this study. The method was based on charge transfer complex formation between the drug, which acted as an ndonor, and chloranilic acid, which acted as a -acceptor in a non-aqueous solvent. The complex stoichiometry was found to be 1:1 (chloranilic acid : cephalexin) with maximum absorption at a wavelength of 520 nm. The complex obeyed Beer’s law. The thermodynamic parameters of the charge transfer complex between chloranilic acid and cephalexin were also elucidated. The thermodynamic parameters investigated include free energy change, enthalpy, entropy, molar absorptivity and stability constant. Results of the study indicated that the complex formed was more stable at lower temperatures but increase in temperature facilitated complex formation. The method was successfully applied in the analysis of commercially available cephalexin capsules without interference from its excipients, with good precision and reproducibility, compared with the official assay method (non-aqueous titration) described for cephalexin in the compendium.