Determination of Technetium-99 in Aqueous Solutions by Inductively Coupled Plasma Mass Spectrometry: Effects of Chemical Form and Memory

Abstract

The effects of chemical form and instrumental memory on the determination of technetium-99 ( ⁹⁹ Tc) in aqueous environmental samples by ICP-MS were investigated. Using an assortment of cationic, anionic and neutral Tc and Re complexes, a comparison of the ICP-MS method with the established methods of liquid scintillation counting (LSC) for Tc and neutron activation analysis (NAA) for Re gave lower than expected Tc and Re values by ICP-MS owing to loss of sample in the delivery system. Oxidation of the complexes prior to analysis and the addition of Triton X-100 to the sample solution eliminated this problem. Instrumental memory, resulting from interactions of ⁹⁹ Tc with the peristaltic pump tubing and the alumina injection port tube, caused significant increases in the background count rate during analysis. Aspiration with a nitric acid solution between sample runs to clean the system effectively eliminated this problem. These techniques were applied to simulated tap water and actual river water samples, and the accuracy was assessed through LSC and spike recovery experiments. The detection limit of the ICP-MS method was found to be 0.6 ppt with an RSD of less than 10%, and these results were within 4% of the LSC results. The sensitivity of the ICP-MS method for the determination of ⁹⁹ Tc is much superior to that of the alternative radioanalytical methods when accounting for the data acquisition time for identical, low-concentration samples such as are often found in the environment.