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 x 10(-10) M and 2.2 x 10(-11) M for SWP and DPP, respectively. Doxazosin could be determined over the 8 x 10(-11) to 5 x 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 x %, n = 5) and added to human urine after preseparation of the drug on a solid phase LC18 cartridge.