Optimised method for the routine determination of Technetium-99 in environmental samples by liquid scintillation counting

A method has been developed for the routine determination of 99Tc in a range of environmental matrices using 99mTc (t1/2=6.06 h) as an internal yield monitor. Samples are ignited stepwise to 550C and the 99Tc is extracted from the ignited residue with 8 M nitric acid. Many contaminants are co-precipitated with Fe(OH)3 and the Tc in the supernatant is pre-concentrated and further purified using anion exchange chromatography. Final separation of Tc from Ru is achieved by extraction of Tc into 5% tri-n-octylamine in xylene from 2 M sulphuric acid. The xylene fraction is mixed directly with a commercial liquid scintillant cocktail. The chemical yield is determined through the measurement of 99mTc by gamma spectrometry and the 99Tc activity is measured using liquid scintillation counting after a further two weeks to allow decay of the 99mTc activity. Typical recoveries for this method are in the order 70-95%. The method has a detection limit of 1.7 Bq kg-1 based on a 2 h count time and a 10 g sample size. The chemical separation for 24 samples of sediment or marine biota can be completed by one analyst in a working week. A further week is required to allow the samples to decay before determination. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)