Adsorption-regulated electrochemical determination of 17α-ethinylestradiol based on a Cu@Fe2O3 composite-modified electrode.

17α-Ethinylestradiol (EE2) is a phenolic estrogenic endocrine disruptor widely distributed in aquatic environments; therefore, sensitive and reliable analytical methods for its environmental monitoring are required. Herein, an adsorption-regulated electrochemical sensing strategy is proposed for the quantitative determination of EE2 using a Cu@Fe2O3 composite-modified glassy carbon electrode. The synergistic Cu-Fe2O3 interface effectively enhances interfacial affinity toward EE2 molecules and facilitates proton-coupled electron transfer during electrochemical oxidation, resulting in an analytical signal predominantly governed by interfacial adsorption rather than diffusion. Under optimized conditions, the modified electrode exhibits a good linear response to EE2 in the concentration range of 0.10 -20.00 μM with a detection limit of 0.033 μM. Electrochemical mechanism studies indicate that the oxidation of EE2 is an irreversible, adsorption-controlled process. The proposed sensor shows satisfactory selectivity, good repeatability, and long-term stability. Moreover, it was successfully applied to the determination of EE2 in real water samples with acceptable recovery values. This study highlights the crucial role of interfacial adsorption in electrochemical signal amplification and provides a versatile analytical strategy for the sensitive detection of phenolic endocrine-disrupting compounds in complex water matrices.