Extractive electrospray ionization mass spectrometry for sensitive detection of gaseous radioactive iodine-129

Abstract

A rapid method based on extractive electrospray ionization mass spectrometry (EESI-MS) has been developed for quantitative detection of trace radioactive molecular iodine-129 (¹²⁹I₂) in negative ion detection mode in ambient air. For actual air samples, gaseous ¹²⁹I₂ was completely converted into iodine-129 ions (¹²⁹I⁻) by an excess of Na₂SO₃ solution. By adding excess amounts of ¹²⁷I₂ into the solution, the ¹²⁹I⁻ ions formed triiodide ion complexes (i.e.^129+127*2I₃⁻) which were subjected to tandem mass spectrometry experiments to exclude false positives. Quantification of iodine-129 was achieved by quantitatively measuring the characteristic fragment (i.e., ¹²⁹I⁻) of the triiodide ion complexes. The calibration curve showed a good linearity within an relatively wide concentration range of 0.01–1000 ppb (R² = 0.991), a limit of detection (LOD) of 4.5 ppt and a relative standard deviation (RSD) of 4.0–13.1% (n = 5). The spiking recovery of this method was found to be 82.6–110.5%. The method had also been successfully applied to detecting the trace amount of gaseous ¹²⁹I₂ released in a simulated nuclear leakage accident, showing a satisfactory result for the tested gaseous samples. The experimental data demonstrated that EESI-MS was a useful tool for quantitative measurement of radioactive iodine in cases such as nuclear leakage, nuclear explosions and related scenarios.