Improved approach for routine monitoring of 129I activity and 129I/127I atom ratio in environmental samples using TMAH extraction and ICP-MS/MS

Abstract

To reconstruct 131I deposition and identify the source of radioiodine due to the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, 129I activity and 129I/127I atom ratio should be obtained by preparing and analyzing large numbers of samples economically. In this study, great efforts were made to realize mild TMAH (tetramethyl ammonium hydroxide) extraction of environmental samples at 90 °C to obtain solutions suitable for the following triple-quadrupole inductively coupled plasma-mass spectrometry (ICP-QQQ) MS/MS mode analysis. After releasing iodine from organic matter in the TMAH extraction solution via K2S2O8 oxidation, organic matter was removed effectively by solvent extraction and back-extraction to avoid a serious matrix effect during ICP-QQQ analysis. At the same time, interfering elements, especially, Mo, Cd, and In were also removed effectively, to avoid their undesirable interferences during mass spectrometric analysis. In addition, 0.01% (NH4)2SO3 was selected to introduce I− into ICP-QQQ to ensure there was no memory effect and a stable signal was gotten. Subsequently, ICP-QQQ MS/MS mode was applied to further eliminate polyatomic interferences (127I(H2 and D)+, 97MoO2+, 113InO+, and 113CdO+) and isobaric interference from 129Xe+. Finally, the developed method was successfully applied to measure 129I/127I atom ratios ((2.61–27.0) × 10−7) and 129I activities (3.51–11.4 mBq kg−1) in soil samples. The developed method allows a greater number of ordinary laboratories to participate in the field of radioiodine analysis.