Flow Injection-Spectrophotometric Determination of Trace Amounts of Iodide by Its Catalytic Effect on the 4, 4′-Bis(dimethylamino)-diphenylmethane- Chioramine T Reaction

A flow injection analysis method is proposed for the spectrophotometric determination of trace amounts of iodide based on its catalytic effect on the oxidation of 4, 4′-bis(dimethylamino)diphenylmethane (tetrabase) by Chloramine T in a weakly acidic solution. Iodide in water samples can be determined at a sampling rate of 85 h-1 with 300μl sample injections. The detection limit is 0.1μg l-1 and the calibration graph for iodide is linear up to 2μg l-1, showing a slightly negative deviation in the higher concentration range. The relative standard deviations are 2.8 and 0.8% for 0.40 and 4.0μg l-1 iodide, respectively. Although free iodine shows a somewhat lower catalytic effect and iodate no catalytic effect up to at least 50μg l-1 as iodine, these species show the same effect as iodide upon being reduced with thioacetamide in an acidic solution. The procedure has been applied to the determination of iodide in natural water samples as well as iodine impurity in both distilled and redistilled water samples. It has also been used to examine iodine contamination in ambient air.