Speciation analysis of 129 I in seawater by carrier-free AgI-AgCl coprecipitation and accelerator mass spectrometric measurement

• Published in: Analytical Chemistry
• Main Authors: Luo, Maoyi, Hou, Xiaolin, He, Chaohui, Liu, Qi, Fan, Yukun
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Chromatographic analysis; Coprecipitation; Iodine; Mass spectrometry; Reliability analysis; Seawater; Separation; Silver; Silver alloys; Silver halides; Norwegian Sea
• Online Access: https://orbit.dtu.dk/en/publications/9d6b7a92-b03e-4d15-ad50-82ecd141f031; https://doi.org/10.1021/ac400060q

A rapid and simple method was developed for speciation analysis of 129I in seawater by selective coprecipitation of carrier-free iodide and accelerator mass spectrometry (AMS) measurement of 129I. Iodide was separated from seawater and other species of iodine by coprecipitation of AgI with Ag2SO3, AgCl, and AgBr by addition of only 100 mg/L Ag+ and 0.3 mmol/L NaHSO3 at pH 4.2-5.5. The separation efficiency of iodide was more than 95%, and crossover between 129IO3- and 129I- fractions is less than 3%. Iodate and total inorganic iodine were converted to iodide by use of NaHSO3 at pH 1-2 and then separated by the same method as for iodide. Ag2SO3 in the coprecipitate was removed by washing with 3 mol/L HNO3 and the excess AgCl and AgBr was removed by use of diluted NH3, and finally a 1-3 mg precipitate was obtained for AMS measurement of 129I. The recovery of iodine species in the entire procedure is higher than 70%. Six seawater samples collected from the Norwegian Sea were analyzed by this method as well as a conventional anion-exchange chromatographic method; the results from the two methods show no significant difference (p = 0.05). Because only one separation step and fewer chemicals are involved in the procedure, this method is suitable for operation on board sampling vessels, as it avoids the transport of samples to the laboratory and storage for a longer time before analysis, therefore significantly improving the analytical capacity and reliability of speciation analysis of 129I. This improvement can stimulate oceanographic tracer studies of 129I. © 2013 American Chemical Society.