Chitosan/Colloid Au Modified Gold Film Microelectrode for Iodide Determination

A simple electrochemical method for iodide detection using chitosan/colloid Au modified gold film microelectrode was developed. The modified electrode was prepared by coating chitosan/colloid Au composite on the surface of a gold film microelectrode, which was fabricated through a microfabrication procedure. In acidic conditions, -NH2 groups on chitosan could be protonated into -NH3+ which has a strong electrostatic attraction with I–. In addition, colloid Au particle could improve the response signal and electron transfer efficiency of the modified electrode. Transmission electron microscopy (TEM) was employed to investigate the colloid Au and the chitosan/colloid Au composite. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) were used to characterize the bare and the chitosan/colloid Au modified gold film microelectrodes. The sensing performance of the chitosan/colloid Au modified microelectrode toward iodide was evaluated in a 0.1 mol·L–1 KH2PO4 (pH=2.5) solution by voltammetry and the obtained voltammetric response increased proportionally with iodide concentration in the range of 3.32×10–7 mol·L–1~1.57×10–2 mol·L–1 with a correlation coefficient of 0.9996. The detection limit was 1.20×10–7 mol·L–1 (3S/N). Compared with the commercial iodide selective electrode, it is more sensitive especially at low concentrations. The modified electrode also demonstrated excellent discrimination against possible interference from chloride, bromide and other potential coexistent ions. The microelectrode was also evaluated by analyzing iodide ion content in a commercial dietary supplement and satisfactory results were obtained for the real sample analysis.