Electroanalytical study and square wave voltammetric techniques for the determination of β-blocker timolol at the mercury electrode

An electroanalytical study of timolol in Britton-Robinson buffer is described. The reduction process on the hanging mercury drop electrode gives rise to two adjacent peaks above -1.0 V (versus Ag/AgCl), the latter on the background discharge, within the entire pH range studied (1.8-10.5), the polarographic pK(a) value obtained was 6.75. The results proved that the reduction of timolol is irreversible and the limiting current is adsorption controlled. The dependence of the peak current on concentration was studied by means of different polarographic and voltammetric techniques. Using adsorptive stripping square wave voltammetry (AdS-SWV), the height for the first peak was proportional to the concentration of timolol in two Linear ranges: 1.0x10(-9) to 1.2x10(-8) M and 1.2x10(-8) to 1.1x10(-7) M, the 3 sigma detection limit being 6.6x10(-10) mol l(-1). For square wave polarography (SWP) the linear range and the detection limit were 4.0x10(-8) to 3.0x10(-6) M with two different slopes and 2.5 x 10(-8) M, respectively. A mechanism is proposed for the reduction of timolol. Two procedures, based on SWP and AdS-SWV, were developed for the determination of timolol in ophthalmologic drops. (C) 1999 Elsevier Science B.V. All rights reserved.