Organically Bound Tritium Analysis in Environmental Samples

Many methods allow analysing the various forms of tritium in environmental samples; however, there are no published standard methods for measuring organically bound tritium (OBT). Furthermore, there are no certified reference materials of OBT for environmental samples. In environmental samples (plants and animals), the measurement of the various tritium fractions requires extraction of the free water, often through freeze drying processes. Combustion of the dry sample is then carried out to recover organically bound tritium in the combustion water. By measuring these water fractions, the tissue-free water tritium (TFWT) and the OBT concentration can be assessed. However, these techniques are tricky and sometimes not available in all monitoring labs. Indeed, most of them measure only the TFWT fraction in food samples, such as wine or milk. Researches to promote the use of validated procedures are on-going in several countries. However, for almost all comparison exercise organisers it is difficult on a yearly basis to provide the samples and to realise the statistical treatment of the results. Therefore, to improve OBT analytical skills, an international task group devoted to the improvement of OBT analytical procedures was created to overcome these limitations. For the first exercise about 20 labs from 8 countries were registered. The samples, specially-prepared potatoes, were provided in March 2013 to each participant. Technical information and results from this first exercise are discussed here for all the labs which have realised the five replicates necessary to allow a reliable statistical treatment. From this work an optimised procedure can start to be developed to deal with OBT analysis and will guide subsequent planned OBT trials by the international group.