DETERMINATION OF TC-99, TH-230 AND U-234 IN SOILS BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY USING FLOW-INJECTION PRECONCENTRATION

A new method is described for the determination of Tc-99, Th-230, and U-234 at ultra-trace levels in soils. The method used flow injection (Fl) for on-line preconcentration of Tc-99, Th-230 and U-234 prior to detection using inductively coupled plasma mass spectrometry (ICP-MS). The Fl-ICP-MS method results in greater sensitivity and freedom from interferences compared with direct aspiration into an ICP mass spectrometer. Detection limits are improved by approximately a factor of 10. The FI-ICP-MS method is also faster, less labour intensive and generates less laboratory waste than traditional radiochemical methods. The accuracy of the method was tested for Tc-99 by comparison to liquid scintillation counting and for Th-230 and U-234 by analysis of a US Department of Energy reference soil. Detection limits in the soil for Tc-99, Th-230 and U-234 were 11 mBq g-1 (0.02 ng g-1), 3.7 mBq g-1 (0.005 ng g-1) and 0.74 mBq g-1 (0.003 ng g-1), respectively. Sample preparation, analysis protocol, and method validation are described.