Electrochemical Investigation of the Ferri/Ferrocyanide Redox Couple on EDTA-Carbon Paste Electrodes

This study focuses on evaluating the electrochemical behavior of the ferri/ferrocyanide redox couple [Fe(CN)₆<sup>3-</sup>/Fe(CN)₆<sup>4-</sup>] on EDTA-modified carbon paste electrodes, with the aim of developing a sensitive electrochemical sensor for the detection of trivalent and hexavalent chromium Cr(III,VI). EDTA, a complexing agent well known for its strong affinity for metal ions, was incorporated at a concentration of 10% in the carbon paste to enhance the electrode's ion recognition properties. Electrochemical characterization was performed by cyclic voltammetry in the presence of the ferri/ferrocyanide redox couple, used as a probe to assess electron transfer properties. Electrochemical parameters, including the peak potential difference (ΔEp), the anodic and cathodic peak currents (Ipa, Ipc), and their ratio, demonstrated the improved redox behavior and sensitivity of the modified electrode. The observed improvement is likely due to the complexing functional groups of EDTA, which facilitate stronger interactions between the modified electrode surface and the redox species in solution. Electrochemical impedance spectroscopy supports the voltammetric findings, confirming enhanced charge transfer kinetics at the surface of the modified electrode. The results confirm the potential of this configuration as an effective platform for developing reliable and selective electrochemical sensors for detecting Cr(III,VI) in aqueous media. By studying the electrical quantities ΔEp, the formal standard potential E°, and the Ipa/Ipc current ratio, the developed electrochemical sensors can be optimized.