Analytical study for the charge-transfer complexes of losartan potassium Original Research Article

Studies were carried out, for the first time, to investigate the charge-transfer reactions of losartan potassium (LOS-K) as n-electron donor with the σ-acceptor iodine and various π-acceptors: 7,7,8,8-tetracyanoquinodimethane, 1,3,5-trinitrobenzene, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, p-chloranilic acid, tetracyanoethylene, 2,3,5,6-tetrabromo-1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, and 2,4,7-trinitro-9-fluorenone. Different colored charge-transfer complexes and radical anions were obtained. Different variables affecting the reactions were studied and optimized. The formed complexes and the site of interaction were examined by UV–vis, IR, and 1H NMR techniques, and computational molecular modeling. The formation of the colored complexes were utilized in the development of simple, rapid and accurate spectrophotometric methods for the analysis of LOS-K in pure form as well as in its pharmaceutical tablets. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9985–0.9998) were found between the absorbances and the concentrations of LOS-K in the range of 2–200 μg ml−1. The limits of assays detection ranged from 0.61 to 19.65 μg ml−1. No interference could be observed from the co-formulated hydrochlorothiazide (HCTZ), as well as from the additives commonly present in the tablets. The methods were successfully applied to the analysis of tablets from different manufacturers that contain LOS-K, alone or combined with HCTZ, with good accuracy and precision; the recovery percentages ranged from 98.96 ± 1.62% to 101.58 ± 1.29%. The results were compared favourably with the reported method.