A. Arranz et al., Electroanalytical study and square wave voltammetric techniques for the determination of beta-blocker timolol at the mercury electrode, ANALYT CHIM, 389(1-3), 1999, pp. 225-232
An electroanalytical study of timolol in Britton-Robinson buffer is describ
ed. 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 back
ground discharge, within the entire pH range studied (1.8-10.5), the polaro
graphic pK(a) value obtained was 6.75. The results proved that the reductio
n of timolol is irreversible and the limiting current is adsorption control
led. The dependence of the peak current on concentration was studied by mea
ns 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: 1.0
x10(-9) to 1.2x10(-8) M and 1.2x10(-8) to 1.1x10(-7) M, the 3 sigma detecti
on limit being 6.6x10(-10) mol l(-1). For square wave polarography (SWP) th
e 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 prop
osed for the reduction of timolol. Two procedures, based on SWP and AdS-SWV
, were developed for the determination of timolol in ophthalmologic drops.
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