Kinetic catalytic determination of trace levels of iodide based on the oxidation of basic dyes with hydrogen peroxide monitored potentiometrically using simple PVC electrodes

Four sensitive catalytic potentiometric methods have been developed for trace levels determination of iodide based on its catalytic effects on the oxidation of four dyes: viz. variamine blue (VB), rhodamine B (RB), methylene blue (MB) and malachite green (MG), with H₂O₂ in H₃PO₄ medium at 25 ± 0.5 °C. The catalyzed reaction rates were estimated potentiometrically by monitoring the potential of the corresponding dye-PVC ion selective electrodes. To select the optimized reaction conditions offering the highest sensitivity of the method, parallel studies were carried out on each dye catalyzed reaction including: the effect of reactant concentration, reaction medium and temperature. The working calibration curves were linear over the concentration range from 0.32 to 2.54 mg L⁻¹ iodide for VB method and from 3.2 to 12.7 mg L⁻¹ for other ones. The tolerance limits of more than 20 interfering species were listed indicating the high selectivity of the method. Trace iodide in edible salt and pharmaceutical samples was determined without the need for separation or preconcentration procedures.