Mass-spectrometric determination of iodine-129 using O 2 -CO 2 mixed-gas reaction in inductively coupled plasma tandem quadrupole mass spectrometry.

This paper presents a mass-spectrometric method for determining the radionuclide iodine-129 ( 129 I) 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 O 2 and CO 2 . Thus far, mass spectrometry analysis of trace amounts of 129 I has been hampered by the presence of xenon-129 ( 129 Xe) and the formation of polyatomic ions from excess amounts of stable isotope 127 I. In this study, flowing a mixture gas of O 2 and CO 2 into the dynamic reaction cell (Q2) successfully removed both 129 Xe interference and polyatomic interference ( 127 IH 2 ) in the analysis of 129 I in ICP-MS/MS. The resulting ratio of (background noise of m/z 129)/ 127 I was 4.6 × 10 -10  ± 3.3 × 10 -10 , which enables the analysis of 10 mBq/L of 129 I in the presence of 100 mg/L of stable 127 I 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.