Determination of 129I in Fukushima Soil Samples by ICP-MS with an Octopole Reaction System

A method was developed for the determination of I-129 in soil samples that uses an ICP-MS equipped with an octopole reaction system. Oxygen was used as the reaction gas for reducing the background intensity of m/z 129, principally by Xe-129(+). The contribution of polyatomic ions, such as (IH2)-I-127+, could be effectively corrected for by assuming a production ratio ((IH2)-I-127+/I-127(+) = 3 x 10(-8)). The measured I-129/I-127 ratios in a NIST standard solution and Fukushima soil samples are consistent with the expected value within the analytical error. This method provides a powerful tool for investigating radioiodine contamination in Fukushima and elsewhere.