Study of the adsorptive stripping voltammetric behaviour of the antihypertensive drug Doxazosin

Two methods for the determination of anti-hypertensive drug Doxazosin by differential pulse polarography (DPP) and square wave polarography (SWP) based on adsorptive stripping techniques, using a hanging mercury drop electrode are described. In both the techniques a polarographic peak is obtained at −1.33 and −1.41 V, respectively, which corresponds to the reduction of the azomethine group in Britton-Robinson buffer at pH = 5.75, after short preconcentration periods and at accumulation potential of 0.24 V. Several electroanalytical techniques are used to explore the redox behaviour; the system is irreversible and fundamentally controlled by adsorption. The detection limits were 6.4 × 10−10M and 2.2 × 10−11 M for SWP and DPP, respectively. Doxazosin could be determined over the 8 × 10−11 to 5 × 10−10 M range by means of DPP. The detection limit obtained is 0.01 ng ml−1, fifty times smaller than the best value found in the bibliography using chromatographic techniques. The procedure is applied to the determination of Doxazosin in tablets 2 mg (s.d. = 1.5 × %, n = 5) and added to human urine after preseparation of the drug on a solid phase LC18 cartridge.