In order to determine organically bound tritium (OBT) from environmental samples, these must be converted to water, measurable by liquid scintillation counting (LSC). For this purpose we conducted some experiments to determine OBT level of a grass sample collected from an uncontaminated area. The studied grass sample was combusted in a Parr bomb. However usual interfering phenomena were identified: color or chemical quench, chemiluminescence, overlap over tritium spectrum because of other radionuclides presence as impurities (14C from organically compounds, 36Cl as chloride and free chlorine, 40K as potassium cations) and emulsion separation.

The paper summarizes results of physico-chemical analyses of initial combustion water and of purified combustion water using 5 methods (distillation with chemical treatment, lyophilisation, chemical treatment followed by lyophilisation, azeotropic distillation with toluene and treatment with a volcanic tuff followed by lyophilisation), determining the value of pH, conductivity and content of some anions (SO4-2, Cl-, NO3-) and cations (Na+, K+, Ca+2, Mg+2, iron, chromium, nickel and copper). Afterwards, each sample was measured, and OBT measured concentration, together with physico-chemical analysis of the water analyzed, revealed that the most efficient method applied for purification of the combustion water was the method using chemical treatment followed by lyophilisation.