Binuclear Schiff Base Complex of Manganese(III) as a Neutral Carrier for a Highly Selective Iodide Electrode

A new highly selective iodide electrode incorporating a binuclear manganese(III) complex, bis(salicylaldehyde-aminopropanol)dichloroaceticdimanganese(III) [Mn(III)2-BSAPDCA], as a neutral carrier is described. The electrode displays an anti-Hofmeister selectivity sequence: iodide » perchlorate > salicylate > thiocyanate > nitrate > bromide > nitrite > chloride > sulfate. The excellent selectivity for iodide is related to a direct interaction between the central Mn(III) atom and iodide and a steric effect associated with the structure of the carrier, which is supported by UV spectroscopy and AC impedance techniques. The electrode exhibits a near-Nernstian potentiometric linear response range to iodide from 1.0 × 10–1 to 2.0 × 10–5 mol/L with a detection limit of 8.0 × 10–6 mol/L and a slope of–60.3 mV/decade in pH 3.0 of phosphate buffer solutions at 20°C. From a comparison of the potentiometric response characteristics between a binuclear manganese(III) complex, Mn(III)2-BSAPDCA, and a mononuclear manganese(III) complex, Mn(III)-BSAPB, an enhanced response towards iodide from a binuclear metallic complex-based electrode was observed. The electrode, based on binuclear manganese(III) complex, was successfully applied to the determination of inorganic total iodine in iodized table salt with satisfactory results.