The electrooxidative behaviour of tamoxifen (Tam) and 4-hydroxytamoxifen (TamOH) was investigated by cyclic (CV), differential-pulse adsorptive anodic stripping (DPAdAS) and square-wave adsorptive anodic stripping (SWAdAS) voltammetric techniques. The anodic oxidation peak of Tamoxifen was attributed to the cyclization reaction to form the corresponding phenanthrene derivative and the mechanism of oxidation was postulated on the basis of controlled potential electrolysis and isolation of the oxidative product. Oxidative stripping analysis was successfully applied to the determination of tamoxifen in a bulk pharmaceutical formulation, and sensitivity in human urine and serum was validated. The achieved limits of detection (LOD) of bulk tamoxifen were 1.8 × 10–6 mol L–1 and 2.4 × 10–6 mol L–1 for DPAdAS and SWAdAS, respectively. The LOD values for tamoxifen in human urine and serum sample analysis were 4.75 × 10–7 mol L–1 and 2.63 × 10–7 mol L–1 and 1.98 × 10–7 mol L–1 and 3.28 × 10–7 mol L–1 for DPAdAS and SWAdAS, respectively. 4-hydroxytamoxifen is oxidised at more positive potentials than Tamoxifen, separated from the Tamoxifen stripping peak, and its adsorption to the glassy carbon electrode is less pronounced. This affects the ability to determine this important phase I metabolite in serum and urine samples
