Application of a nanoporous gold electrode for the sensitive detection of copper via mercury-free anodic stripping voltammetry

This paper describes how a new mercury-free alternative electrode material, nanoporous gold (NPG), was applied to improve the performance of detecting trace metals in stripping voltammetry. The NPG electrode was obtained by dealloying Zn from Au _x Zn_1–x in a 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl₂-EMIC) ionic liquid. To prevent electrode fouling from surfactant adsorption, the short carbon-chain organothiol (3-mercaptopropyl)sulfonate (MPS) was selected to modify the NPG electrode through the formation of a self-assembled monolayer (SAM). The MPS-modified NPG (MPS@NPG) electrode not only significantly enhanced the sensitivity in detecting Cu²⁺ but also effectively prevented electrode surface fouling from surfactant adsorption. The electrode is easy to prepare and can be readily renewed after each stripping experiment. The dynamic range of calibration curve, y = 58.76x (in µA µM^–1) + 3.90 (R ² = 0.999), showed very linear behavior with slope of 58.76 µA µM^–1 (0.1-5 µg L^–1). The detection limit is as low as 0.002 µg L^–1 (0.031 nM). Non-ionic, anionic, and cationic surfactants were found to have no effect on Cu²⁺ detection when using the MPS@NPG electrode as a sensing probe. This method was applied to determining the Cu²⁺ in a reference material and three real water samples. The results agreed satisfactorily with the certified values.