[16p-Z34-1~15] CS.1 Code-sharing Session of 2.4 & 7.5

▼ [16p-Z34-15] Speciation Analysis of Iodine-129 in Seawater by Coprecipitation and Accelerator Mass Spectrometry

〇(D)Yuanzhi Qi¹, Hiroyuki Matsuzaki¹ (1.The Univ. of Tokyo)

Keywords:iodine-129, speciation analysis, seawater

A simple and rapid coprecipitation method combined with accelerator mass spectrometry (AMS) measurement was improved for inorganic speciation analysis of ¹²⁹I in seawater. Iodide was successfully separated from seawater just by adding a certain amount of carrier (0.6 mg) and 100 mg/L Ag⁺ with the separation efficiency high to 95%. When the concentration differences of ¹²⁹I^- and ¹²⁹IO₃^- are huge, slight crossover during the separation process can introduce significant analytical error. In order to remove the remaining I^- in supernatant seawater in last step, AgI is coprecipitated with Ag₂SO₃, AgCl, and AgBr after adding 0.6 mg carrier, 100 mg/L Ag⁺ and 0.3 mmol/L Na₂SO₃ at pH about 4.0, which decrease the crossover between ¹²⁹I^- and ¹²⁹IO₃^- to 0.05%. Iodate in the supernatant was converted to iodide by Na₂SO₃ at pH 1-2 and then separated by coprecipitation, with the 91% separation efficiency. ¹²⁹I of total inorganic iodine was analyzed by the same procedure as for iodate. Two seawater samples collected from the Indian Ocean were analyzed by this improved method, and the results showed that the concentration of ¹²⁹I^- is significantly high than the concentration of ¹²⁹IO₃^- in seawater. Three seawater samples at different depths of the Pacific Ocean were used to analyze ¹²⁹I of total inorganic iodine by this method and solvent extraction and back extraction method, and the results showed no significant difference (p=0.05 for t-test) between two methods.