EVALUATION OF STORAGE-CONDITIONS FOR TRITIATED-THYMIDINE AS REFERENCEORGANICALLY-BOUND TRITIUM IN URINE

Interlaboratory intercomparison exercises have used tritiated thymidin e as a reference material for organically-bound tritium (OBT) measurem ents in urine. We have examined the effects of storage conditions on t he degradation behavior of tritium from OBT to tritiated water (HTO) i n artificial and natural human urine samples. Tritiated thymidine deco mposed less readily in artificial urine than natural urine samples. ?h e degradation rate of tritiated thymidine in artificial urine, at -20 degrees C, is about 10% for the first month. The rate of tritium conve rsion from OBT to HTO is the same at 4 degrees C, but this storage tem perature is less preferable, because of the danger of microbial contam ination in the reference samples. The storage of the reference urine s amples beyond three months after the preparation date is not recommend ed for quality control measurement data.