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

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.