Method for the detection of Tc in seaweed samples coupling the use of Re as a chemical tracer and isotope dilution inductively coupled plasma mass spectrometry

Abstract

The analysis of artificial radionuclide 99Tc in environmental samples requires of a chemical separation due to its low concentration, and therefore the use of a chemical yield tracer is peremptory. From the practical viewpoint, Re could be used for these purposes, due to the chemical similarities between Re and Tc. Thus, the use of a radioactive tracer for Tc recovery calculation could be avoidable. However, results from the more recent intercomparison exercise shows that the use of Re as a chemical yield tracer appears to underestimate the Tc concentration relative to the result obtained with isotopes of Tc. In this work, we show the methodology used for designing a simple separation method for the measurement of 99Tc in environmental samples. Tc recovery is estimated throughout the Re recovery calculation by the ID-ICP MS technique. For chemical separation, a chromatographic resin has been used. Interfering elements are removed using a resin washing step carefully designed to avoid any element fractionation between Re and Tc, being this step of major importance to assure the equivalence of the chemical recoveries for both elements. Such an agreement was tested using 5 replicates of five seaweed samples. The average recoveries for 95mTc and Re were 93±6% and 95±7%, respectively, those were within the uncertainty intervals for each other. The results here explained demonstrated the possibility of applying Re chemical recoveries to calculate the Tc concentrations with the advantage of not introducing systematic errors.