Development of a copper-modified iron electrode electrochemical sensor for sensitive detection of oxalic acid

A copper-modified iron electrode was developed as a simple and effective electrochemical sensor for detecting oxalate ions. The Fe/Cu electrode was fabricated via a simple immersion method and characterized using X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy (FESEM-EDX). Characterization results confirmed the uniform distribution of copper on the iron surface, forming a fine granular structure that enhances electrocatalytic activity toward oxalate oxidation while improving electrode stability and durability. XRD analysis revealed characteristic diffraction peaks of Cu at approximately 2θ = 43.8°, 50.9°, and 74.4°, confirming the presence of a copper layer on the iron surface. The electrochemical performance of the Fe/Cu electrode for oxalate detection was evaluated using cyclic voltammetry, differential pulse voltammetry, and amperometry in 0.1 M phosphate-buffered saline (PBS, pH 9). The results demonstrated a significant increase in oxidation current intensity in the presence of oxalate. Further amperometric studies revealed that the Fe/Cu electrode exhibited a wide linear range from 0.1 to 0.5 mM and 0.6–2 mM, with a detection limit of 1.95 μM. Selectivity tests demonstrated that the presence of potential interfering species such as glucose, uric acid, ascorbic acid, urea, and heavy metal ions (Pb²⁺, Cd²⁺, Zn²⁺, Fe³⁺, and Fe²⁺) did not affect oxalate detection. Additionally, the sensor exhibited high reproducibility (RSD = 1.37 %), good repeatability (RSD = 2.10 %), and excellent stability, with only a 3.2 % signal decrease after one month, making it a promising platform for practical applications in food safety and environmental analysis.