Colorimetric determination of beta-blockers in pharmaceutical formulations

A simple, accurate, precise and sensitive colorimetric method for the determination of some beta-blockers as atenolol (Ateno), metoprolol (Metop), sotalol (Sot) and nadolol (Nad) is described. This method is based on the formation of charge transfer complex with 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) in methanolic-aqueous (for Ateno and Metop) or acetone-aqueous (for Sot and Nad) medium [30% (v/v)]. The orange color products are measured at 485, 470, 465 and 462 nm for Ateno, Metop, Sot and Nad, respectively. The optimization of various experimental conditions is described. Beer's law is obeyed in the range 0.4-60 microgram ml(-1) while that obtained applying Ringbom is 0.8-56 microgram ml(-1). The molar absorptivity, Sandell sensitivity, detection and quantification limits are calculated. The results obtained showed good recoveries of 99.5+/-1.1, 100.3+/-1.2, 100.5+/-1.0 and 99.3+/-1.1% with relative standard deviations of 0.74, 0.98, 1.15 and 0.87% for Ateno, Metop, Sot and Nad, respectively. Applications of the proposed method to representative pharmaceutical formulations are successfully presented.