Development of an organically bound tritium standard

High-concentration factors between seawater and marine organisms have been observed for organically bound tritium (OBT). The absence of an available OBT standard impedes the validation of an analytical method for environmental samples. This paper describes the secondary standardisation of tritiated thymidine, which was chosen to act as an OBT standard, using liquid scintillation counting. Traceability was provided by using internal standards of tritiated water (HTO). The assumption that the counting efficiencies for tritiated thymidine and HTO were identical was tested with separate quench curves. The rate of self-decomposition for tritiated thymidine, which resulted in an activity concentration of tritiated thymidine lower than the total tritium activity concentration, was determined.