Spectrophotometric determination of iodide at the 10–6mol l–1level by solvent extraction with methylene blue

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Abstract
Iodide is separated from other chemical species by its oxidation and subsequent extraction into carbon tetrachloride. The proposed method is based on the extraction of the back-extracted iodide into 1,2-dichloroethane as an ion pair with methylene blue. When a 40-ml sample solution is used, the apparent molar absorptivity for iodide is 3.15 × 105 l mol–1 cm–1 and the Sandell sensitivity for a 0.001 absorbance is 4.3 × 10–4µg cm–2 of l– at 657 nm. A linear calibration graph is obtained over the range 7.5 × 10–8–3 × 10–6 M iodide and the relative standard deviation is 0.87% at the 1.5 × 10–6 M iodide level. The proposed method was successfully applied to the determination of various amounts of iodide in natural water samples.

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