Speciation analysis of both inorganic and organic 129I in seawater and its application in the study of the marine iodine cycle

Abstract

A complete protocol is presented for the speciation analysis of ¹²⁹I for both inorganic and organic iodine in seawater using coprecipitation and solid-phase extraction (SPE) combined with accelerator mass spectrometry (AMS). By modifying the iodide separation process and adding a crossover removal step, the improved coprecipitation method significantly reduces the cross-contamination of iodide and iodate to less than 0.05% in the speciation analysis of inorganic ¹²⁹I, with the separation efficiencies of about 95% and 93% for iodide and iodate, respectively. The SPE-DOI method for the dissolved organic ¹²⁹I (DO¹²⁹I) analysis was developed, whereby we report the first direct observation of DO¹²⁹I/DO¹²⁷I atom ratios in seawater in this paper. ¹²⁹I species in seawater from Tokyo Bay were analysed. The ¹²⁹I results demonstrated that our protocol for speciation analysis of ¹²⁹I is reliable and provided new insights into understanding the iodine cycle.