Voltammetric Determination of Sulfur-Containing Compounds in Motor Fuels Using Screen-Printed Carbon Electrodes Modified with Cu–Ag Bimetallic Nanocomposites

Abstract

A voltammetric method was developed for determining sulphur-containing compounds in motor fuels using screen-printed carbon electrodes modified with electrodeposited Cu–Ag bimetallic nanocomposites. The study examined how the Cu/Ag ratio affected surface morphology, phase composition, electron-transfer behaviour, and analytical performance. Modified electrodes prepared by sequential and simultaneous electrodeposition were characterised using scanning electron microscopy, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. The analyses confirmed crystalline Ag, Cu, and Cu₂O phases and showed that the equimolar Cu composition produced the most uniform and developed nanostructure. This composition also exhibited the lowest charge-transfer resistance, indicating enhanced interfacial electron transfer. Under the optimised conditions, the sensor showed a linear response to sulphide over 0.05–2.00 mmol L⁻¹, with R² = 0.998, and a limit of detection of approximately 0.005 mmol L⁻¹, equivalent to about 0.16 mg L⁻¹ as sulphide sulphur. Results obtained for commercial petrol and diesel samples were consistent with those obtained by potentiometric titration and X-ray fluorescence spectrometry, while the reported relative standard deviations were below 9%. The method is intended primarily for electrochemically active sulphur-containing compounds rather than direct total-sulphur determination. Subject to further validation of electrode stability, selectivity, and reproducibility, the Cu–Ag/SPCE platform offers a rapid and comparatively simple approach for fuel-quality screening and potential on-site analytical use.