We developed an analytical method for organically bound 3H (OBT) in biological environmental samples by using noble gas mass spectrometry of 3He produced from 3H. Three environmental samples with background level OBT concentrations were analyzed, and the results agreed well with those by the conventional liquid scintillation counting of electrolyzed combustion water of the samples. This showed that the method is practical and effective.

We also developed an analytical method for non-exchangeable OBT as a combination of pre-treatment of dried samples with free water 3H and our newly developed analytical method for OBT. The repeated analysis of a grass sample with moderate 3H concentration had smaller variance of results for non-exchangeable OBT than for OBT. The sum of non-exchangeable and exchangeable OBT agreed well with OBT measured in the samples. The developed method was successfully applied to terrestrial and marine environmental samples with background 3H levels.