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 E(acc)=-0.7 V versus Ag/AgCl/KCl(s), accumulation duration=60s, pulse-amplitude=70 mV, scan increment=10 mV and frequency=120 Hz. Limits of detection (LOD) and quantification (LOQ) of 5.9x10(-10)M and 1.9x10(-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 8.7x10(-10)M and 3x10(-9)M and LOQ of 2.9x10(-9)M and 1x10(-8)M of ethinylestradiol were achieved in human serum and plasma, respectively.