Mass-spectrometric determination of iodine-129 using O2-CO2 mixed-gas reaction in inductively coupled plasma tandem quadrupole mass spectrometry.

This paper presents a mass-spectrometric method for determining the radionuclide iodine-129 (129I) from the significant amount of interference in inductively coupled plasma tandem quadrupole mass spectrometry (ICP-MS/MS) using a dynamic reaction cell passing a mixture gas of O2 and CO2. Thus far, mass spectrometry analysis of trace amounts of 129I has been hampered by the presence of xenon-129 (129Xe) and the formation of polyatomic ions from excess amounts of stable isotope 127I. In this study, flowing a mixture gas of O2 and CO2 into the dynamic reaction cell (Q2) successfully removed both 129Xe interference and polyatomic interference (127IH2) in the analysis of 129I in ICP-MS/MS. The resulting ratio of (background noise of m/z 129)/127I was 4.6 × 10-10 ± 3.3 × 10-10, which enables the analysis of 10 mBq/L of 129I in the presence of 100 mg/L of stable 127I without chemical separation. The detection limit of this method was 0.73 mBq/L (= 0.11 ng/L) with an APEX-Q sample inlet desolvation device. For demonstration purposes, spike and recovery analysis of rainwater was performed, and good agreement between the spiked and recovered amounts was achieved.