Cathodic Stripping Voltammetric Determination of Doxazosin in Urine and Pharmaceutical Tablets Using Carbon Paste Electrodes

Abstract

Several voltammetric techniques were used to explore the reductive behaviour of the antihypertensive agent doxazosin on a bare carbon paste (CPE) and a Tenax-modified carbon paste electrode (TMCPE). The results indicate that the process is irreversible and fundamentally controlled by adsorption, which allows doxazosin to be accumulated at the electrode surface. The cathodic adsorptive stripping (AdS) response was evaluated with respect to pH, accumulation variables and instrumental parameters, using differential-pulse (DPV) and square-wave voltammetry (SWV) as redissolution techniques. In both cases, a voltammetric peak close to 0 V in Britton–Robinson buffer (pH 6.6) was obtained after a preconcentration step at 0.55 V for 3 min (2000 rpm) and a subsequent cathodic scan. When the TMCPE was used, the limits of detection were 4.35 × 10 ^{- 11} and 5.18 × 10 ^{- 11} M for AdS–DPV and AdS–SWV, respectively. The deposition time (3 min) was improved relative to that obtained by means of CPE (6 min). Under the optimum operational conditions, the doxazosin reduction peak showed a linear response in the range from 6 × 10 ^{- 11} to 1 × 10 ^{- 9} M by using AdS–DPV, with an RSD of 3.39% for 3 × 10 ^{- 8} M doxazosin solution (n = 10). A method was developed for the determination of doxazosin in human urine and formulations.