Catalytic Detection of Iodide at Cationic Kaolinite Modified Gold Electrode in Presence of Thiosulfate

A gold electrode modified by a thin film of cationic kaolinite was used for the electrochemical detection of iodide in aqueous solution in the presence of thiosulfate. At gold electrode, iodide showed two electrochemical systems in the potential range explored (0.10 V to 0.85 V). The pH‐independent system was assigned to the redox couple I₂/I^? and the pH‐dependent one assigned to the redox couple HIO/ . For increased amount of thiosulfate the oxidation peak intensity of the first system increases sharply followed by the gradual decrease of the reduction peak, due to the chemical reaction between thiosulfate and oxidized iodide. The calibration curve in the presence of excess thiosulfate resulted in an increase of the sensitivity by a factor of 7. To improve this sensitivity, the bare gold electrode was coated by a thin film of an anionic exchanger kaolinite, obtained by grafting the ionic liquid (1‐(2‐hydroxyethyl)‐4‐(tert‐butyl) pyridinium chloride). Accumulation‐detection method yielded a spectacular increase of the oxidation peak current of iodide in the presence of thiosulfate ions. At optimized experimental conditions, a sensitivity of 2.45 μA.μM^?1 and a detection limit of 65 nM were obtained. The method was successfully applied for total iodine determination in povidone?iodine formulation.