Evaluation of storage conditions for tritiated thymidine as reference organically-bound tritium in urine

Abstract

Interlaboratory intercomparison exercises have used tritiated thymidine as a reference material for organically-bound tritium (OBT) measurements in urine. We have examined the effects of storage conditions on the degradation behavior of tritium from OBT to tritiated water (HTO) in artificial and natural human urine samples. Tritiated thymidine decomposed less readily in artificial urine than natural urine samples. The degradation rate of tritiated thymidine in artificial urine, at −20°C, is about 10% for the first month. The rate of tritium conversion from OBT to HTO is the same at 4°C, but this storage temperature is less preferable, because of the danger of microbial contamination in the reference samples. The storage of the reference urine samples beyond three months after the preparation date is not recommended for quality control measurement data.