Preconcentration and voltammetric determination of the antihypertensive doxazosin on a C-8 modified carbon paste electrode

An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. T he process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mecha nism based on the oxidation of the amine group is postulated. Two methods b ased on adsorptive st:ripping (AdS) of doxazosin at the C-8-modified carbon paste electrode (C-8-MCPE), before its voltammetric determination, are stu died, using differential pulse voltammetry (DPV) and square wave voltammetr y (SWV) as redissolution techniques. By means of AdS-DPV and C-8-MCPE, doxa zosin can be determined over the 1.0 x 10(-9) to 3.0 x 10(-8) mol L-1 range with a variation coefficient of 2.2% (2.0 x 10(-8) mol L-1) and a limit of detection of 7.4 x 10(-10) mol L-1. If AdS-SWV is used, a linear range fro m 1.0 x 10(-9) to 4.0 x 10(-8) mol L-1 is obtained, the variation coefficie nt being 2.8% (2.0 x 10(-8) mol L-1, and the limit of detection reached 7.7 x 10(-10) mol L-1. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations.