Determination of Chemical Species of Iodine in Seawater by Radiochemical Neutron Activation Analysis Combined with Ion-Exchange Preseparation

A method for the determination of iodide, iodate, organic iodine, and total iodine in seawater was developed. The behaviors of loading, washing, and eluting of iodide, iodate, and organic iodine in a strongly basic anion-exchange column (AG1-×4, chlorine form) were studied by 131I tracer. Iodide was separated from other iodine species and other ions by directly passing filtered natural seawater through an anion-exchange column, washing with deionized water and 0.5 mol/L KNO3 solution, and eluting with 2.0 mol/L KNO3. Organic iodine was separated by passing seawater through an ion-exchange column after iodate had been converted to iodide by KHSO3 and collecting effluent during loading and washing with deionized water. The iodine content was determined by neutron activation analysis with postirradiation separation using CCl4 extraction. Studies of the effect of chlorine, bromine, and iodine concentrations on the extraction separation show that the recovery of iodine decreases with increasing Br- and Cl- concentrations and decreasing I- concentration. Under the experimental conditions, iodine in seawater was quantitatively recovered, and a 0.2 μg/L detection limit for iodine was obtained. Concentrations of total iodine, I-, IO3 -, and organic iodine in seawater collected from Roskilde Fjord, Denmark, were determined.