Spectrophotometric determination of beta-adrenergic blocking agents in pharmaceutical formulations.

Simple, rapid and sensitive spectrophotometric procedures were developed for the analysis of atenolol, timolol maleate, propranolol hydrochloride, metoprolol tartarate, betaxolol hydrochloride, levobunolol hydrochloride and bisprolol fumarate in pure form as well as in their pharmaceutical formulations. The methods are based on the reaction of these drugs as n-electron donors with the sigma-acceptor iodine, and the pi-acceptors: 7,7,8,8-tetracyanoquinodimethane, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyanoethylene, 2,3,5,6-tetrabromo-1,4-benzoquinone (bromanil) and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil). The obtained charge-transfer complexes were measured at 365 nm for iodine (in 1,2-dichloroethane), at 840, 420, and 470 nm for 7,7,8,8-tetracyan-oquinodimethane, tetracyanoethylene and 2,3-di-chloro-5,6-dicyano-1,4-benzoquinone (in acetonitrile), respectively, and at 450 and 440 nm for bromanil and chloranil (in ethanol), respectively. Due to the rapid development of colors at ambient temperature, the obtained results were used on thin-layer chromatograms for the detection of the investigated drugs. Beer's plots were obeyed in a general concentration range of 4-120 microg ml(-1) with correlation coefficients not less than 0.9991. The proposed procedures could be applied successfully to the determination of the investigated drugs in tablets and ophthalmic solutions with good recovery; percent ranged from 98.03+/-0.98 to 100.30+/-0.90. The association constants and standard free energy changes using Benesi-Hildebrand plots were studied.