Quality assurance of the oceanographic tracers Technetium-99 and Antimony-125: Intercomparisons and recovery tests

Five large seawater samples and two samples of dried seaweed (Fucus sp.) powder have been analyzed radiometrically for low concentrations of 99Tc by five European institutions. Some of the water samples were analyzed further for 125Sb. The overall standard deviation (SD) for 99Tc in the two seaweed samples was 8% and 5%, respectively. The consistency of the seawater results was correlated to the concentration levels. For concentrations > 1 Bq 99Tc m−3, the SD was better than 20%, whereas for the 0.5 Bq m−3 level, 50% SD was observed utilizing all data. It is recommended for future collaborative programmes utilizing 99Tc — and other radionuclides requiring rigorous radioanalytical procedures — that a large, homogeneous sample is identified at an early stage and random sub-samples taken at frequent intervals for intercalibration purposes throughout the period of study. Recovery tests performed at all five laboratories showed no systematic bias in the analysis of 99Tc.