Kinetic determination of iodide in pharmaceutical and food samples

Abstract

A kinetic method for the determination of iodide based on its inhibitory effect on the Pd^II catalysed reaction between ethylenediaminetetraacetic acid (EDTA)–Co^III and the hypophosphite ion is described. The reaction was followed spectrophotometrically by measuring the decrease in the absorbance at 540 nm. Under the optimum experimental conditions of 2.6 × 10^–3 mol dm^–3 Co^III–EDTA, 0.4 mol dm^–3 H₂PO₂^–, pH 3.2 (adjusted with Britton–Robinson buffer), 0.57 µg ml^–1 Pd^II and 20 ± 0.2 °C, iodide was determined in the range 2–28 ng ml^–1. The method was applied to the determination of iodide in pharmaceutical products, iodinated salts, cow's milk and infants' powdered milk.