Contribution of elemental analysis and UV-VIS spectrophotometry to the understanding of E-OBT elimination stage

Tritium exists in environmental samples as: (i) Tissue Free Water Tritium (TFWT) and associated with the organic matter (OBT) under two forms; (ii) bound to oxygen and nitrogen atoms into the material (E-OBT); (iii) bound to carbon atoms into the material (NE-OBT). The analysis of the NE-OBT fraction requires the elimination of E-OBT prior measurement. This operation is generally performed through labile exchange supposing that only isotopic exchange occurs. Most of the time, the recovered exchange water are coloured indicating that other mechanisms arise. To identify and to understand these mechanisms, the combination of two analytical tools, a CHNS-O elemental analyser and a spectrophotometer was used NE-OBT analyses are performed on numerous environmental samples. In this work aliquots of those samples, under their solid form, were taken before and after labile exchange for elemental analysis purposes. In the same time the exchange waters were stored until spectrophotometric measurements. Solid analysis show that an evolution of the elemental composition could occur during the labile exchange with potential analytical impact. Moreover, it gives first ideas on which molecule could be solubilised. This trend is confirmed through spectrophotometric analysis where bands are observed for wavelength characteristics of proteins, amino acids, nucleic acids. Those preliminary results obtained using both techniques are promising but needs confirmation in the near future to determine to which extent an analytical impact could occur and to complete the identification of soluble molecules. (authors)