Adsorptive cathodic stripping voltammetric assay of the estrogen drug ethinylestradiol in pharmaceutical formulation and human plasma at a mercury electrode

The electroreduction of ethinylestradiol at the hanging mercury drop electrode in the Britton–Robinson universal buffer of pH 2–11 was studied and its interfacial adsorptive character onto the mercury electrode surface was identified. A validated simple, rapid, sensitive, specific, precise and inexpensive square-wave voltammetric procedure is described for the determination of ethinylestradiol following its accumulation onto a hanging mercury drop electrode in a Britton–Robinson universal buffer of pH 7. The optimal procedural conditions were: accumulation potential Eacc = −0.7 V versus Ag/AgCl/KCls, accumulation duration = 60 s, pulse-amplitude = 70 mV, scan increment = 10 mV and frequency = 120 Hz. Limits of detection (LOD) and quantification (LOQ) of 5.9 × 10−10 M and 1.9 × 10−9 M bulk ethinylestradiol, respectively, were achieved. The proposed procedure was successfully applied to the quantification of ethinylestradiol in pharmaceutical formulation (Ethinyl-oestradiol® tablets) and in human serum and plasma without the necessity for sample pretreatments and/or time-consuming extraction or evaporation steps prior to the analysis. LOD of 8.7 × 10−10 M and 3 × 10−9 M and LOQ of 2.9 × 10−9 M and 1 × 10−8 M of ethinylestradiol were achieved in human serum and plasma, respectively.