Development of organically bound tritium analysis method with noble gas mass spectrometry

Tritium in biological samples exists as free water tritium and organically bound tritium (OBT). Since those chemical forms have different behavior in the environment, they need to be separately determined. The OBT is generally analyzed by measurement of 3H radioactivity by a liquid scintillation counter (LSC) after combustion of lyophilized sample. However, recent decline of OBT concentration in the general environment makes the measurement with the LSC difficult. We developed an analytical method for OBT in environmental samples by measuring triogenic 3He with a noble gas mass spectrometer, and successfully applied to low-level OBT in samples collected from the current general environment. Typical lower detection limit of this method was 0.02 Bq L-1 combustion water, and an order of magnitude lower than that with the conventional method. This work was supported by contract with Aomori prefecture, Japan. (author)