Chemiluminescence determination of iodide and/or iodine using a luminol–hexadecyltrimethylammonium chloride reversed micelle system following on-line oxidation and extraction

A rapid and sensitive flow method, based on the combination of on-line oxidation–solvent extraction with reversed micellar mediated luminol chemiluminescence detection, was found to be suitable for the determination of iodide in aqueous solution. The flow procedure involved the oxidation of iodide to iodine, extraction of iodine into cyclohexane followed by membrane phase separation, and its chemiluminescence detection using the reaction of iodine with luminol in a reversed micellar solution of hexadecyltrimethylammonium chloride in 6 + 5 (v/v) chloroform–cyclohexane/water (buffered with sodium carbonate). The optimum conditions for iodide oxidation were evaluated using 2-iodosobenzoate as an oxidizing agent and a detection limit of 0.02 ng mL−1 iodide was achieved. Using different oxidants, 2-iodosobenzoate and peroxodisulfate, linear calibration graphs were obtained with dynamic ranges from 5 to 200 and from 50 to 5000 ng mL−1, respectively. The proposed method was also applied to a mixture of iodine and iodide, where iodine was determined directly without using an oxidizing agent, total iodine (iodine + iodide) was determined using an oxidizing agent, and iodide was calculated by difference. The method was applied to the differential determination of iodide and iodine in gargle samples with a precision of ca. 4% relative standard deviation.