In-capillary derivatization and determination of iodine in sodium chloride solution

Abstract

A new capillary electrophoretic (CE) method was developed for the simple and selective determination of iodine in 0.5 mol l⁻¹NaCl. The proposed method is based on the in-capillary derivatization of iodine with thiosulfate ions using the zone-passing technique and direct photometric detection of the iodide and tetrathionate formed. The optimal conditions for the separation and derivatization reaction were established by varying the concentration of iodine, electrolyte pH and applied voltage. The optimized separations were carried out in phosphate electrolyte (pH 6.86) using direct photometric detection at 253.7 nm. Common photometric detection absorbing anions such as Cl⁻, NO₂⁻, S₂O₃²⁻ did not give any interference. Valid calibration (r² = 0.994) is demonstrated in the range 16.5–198.1 mg l⁻¹ of iodine. The detection limit (calculated according to K. Doerffel, Statistik in der analytischen Chemie, 1990) was 11.53 mg l⁻¹ (by iodide peak area) and 8.45 mg l⁻¹ (by tetrathionate peak area). The proposed system was applied to the determination of iodine after oxidation of iodide in underground water.