scope:

This International Standard describes the conditions for the determination of 14C activity concentration in samples of environmental water or of 14C containing water using liquid scintillation counting. The scintillation phenomenon results from interaction of ionizing radiation with solvents and compounds exhibiting fluorescence (scintillators). Both solvents and scintillators constitute the scintillation cocktail. The scintillation mixture is achieved by adding the scintillation cocktail to the test sample in order to obtain a homogeneous mixture. Some examples of methods with sample pretreatment are described in Annexes C and D. NOTE 1 The method is applicable to the analysis of any organic molecule soluble in water that is well mixed with the scintillation cocktail. It may not work for micelles or "large" particles (lipids, fulvic acid, humic acid, etc.) that will be badly mixed with the scintillation cocktail and the water. Some beta energy will be lost without any excitation of the scintillation cocktail and the results will be underestimated. The method is not applicable to the analysis of organically bound 14C ; its determination requires additional chemical processing (such as chemical oxidation, combustion). NOTE 2 14C activity concentrations below 106 Bq.L-1 may be determined without any sample dilution.