Tamoxifen oxidation in unbuffered acidic aqueous–alcoholic media at boron-doped diamond electrodes: experimental and theoretical insights into possible application in electroanalysis

Abstract

Tamoxifen (TAM), a selective oestrogen receptor modulator prescribed for the treatment of breast cancer and endocrine disorders, was investigated in an acidic aqueous-alcoholic unbuffered environment in terms of its oxidation, protonation/deprotonation, electron transfer, and interaction with the charged phase interface. Advanced analysis of TAM oxidation was performed experimentally using a screen-printed boron-doped electrode (SP/BDDE). The study highlights not only the influence of electrochemical pre-treatment of the SP/BDDE surface (O-termination), pH and ethanol content on the irreversible electron transfer in the TAM molecule, but also the ability of differential pulse and elimination voltammetric analysis (DPV and EVLS) to recognize the nature of the ongoing electrochemical processes. The optimal protocol for the most efficient heterogeneous electron transfer for TAM (O-terminated boron-doped diamond) and the mechanism of its oxidation (pH 2, EtOH 7.7% vol.) was proposed. The effect of ethanol content on the oxidation voltammetric signal of TAM has been discussed through the physicochemical properties of aqueous-alcoholic solutions, such as their permittivity, ionic mobility, and viscosity. We identified a distinct rate-determining step for the oxidation process of TAM on carbon and diamond, and we proposed the oxidation mechanism of TAM using quantum chemical (DFT) calculations. The study also shows that the combination of an unbuffered acidic medium and an oxygen-terminated, highly boron-doped diamond electrode represents a robust and practical approach for electrochemical analysis of TAM in real urine samples, offering excellent antifouling properties, stable oxidation peak potentials, and reliable detection of trace-level TAM.