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

To reconstruct 131 I deposition and identify the source of radioiodine due to the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, 129 I activity and 129 I/127 I 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 K2 S2 O8 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 )2 SO3 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 (127 I(H2 and D)+ , 97 MoO2 + , 113 InO+ , and 113 CdO+ ) and isobaric interference from 129 Xe+ . Finally, the developed method was successfully applied to measure 129 I/127 I atom ratios ((2.61-27.0) × 10-7 ) and 129 I 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.