Speciation Analysis of (129)I and (127)I in Aerosols Using Sequential Extraction and Mass Spectrometry Detection

A new analytical method has been developed for speciation analysis of (127)I and (129)I in aerosols collected on polypropylene (PP) filter paper. Iodide, iodate, NaOH soluble iodine, and insoluble iodine were separated from aerosols using sequential extraction, chromatography separation, and alkaline ashing and measured using inductive coupled plasma mass spectrometry (ICP-MS) for (127)I and accelerator mass spectrometry (AMS) for (129)I. Parameters affecting the leaching efficiency and stability of iodine species, such as leaching time and temperature, amount of alkaline reagent for ashing, ashing temperature and time, and iodine protective agent, were investigated and optimized. It was observed that long time water leaching would change inorganic iodine species due to photochemical oxidation of iodide on the PP filter surface. NaOH leaching can only extract less than 60% of iodine from the studied aerosol filters even under heating, implying that total (129)I in aerosol might be underestimated by NaOH leaching. The addition of a reductive agent significantly reduced the loss of iodine during alkaline ashing from more than 35% to 4%, efficiently improving the separation efficiency of iodine in aerosols. Speciation analysis of (129)I and (127)I in aerosol samples collected at Risø, Denmark using the developed method shows that the measured values of total (129)I and (127)I are in good agreement with the sum of all iodine species for each isotope, confirming the reliability of the proposed method. Similar distribution patterns between (129)I and (127)I species show that iodine is enriched in NaOH leachable and insoluble species and depleted in water-soluble species, as observed in all aerosol samples.