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 Tc-99 in a ran ge of environmental matrices using Tc-99m (t(1/2)=6.06 h) as an internal yi eld monitor. Samples are ignited stepwise to 550 degrees C and the Tc-99 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 precon centrated and further purified using anion exchange chromatography. Final s eparation of Tc from Ru is achieved by extraction of Tc into 5% tri-n-octyl amine in xylene from 2 M sulphuric acid. The xylene fraction is mixed direc tly with a commercial liquid scintillant cocktail. The chemical yield is de termined through the measurement of (99)mTc by gamma spectrometry and the( 99)Tc activity is measured using liquid scintillation counting after a furt her two weeks to allow decay of the (99)mTc activity. Typical recoveries fo r 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 chemica l 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 sam ples to decay before determination. (C) 1999 Elsevier Science B.V. All righ ts reserved.