Estimation of the formation rates of polyatomic species of heavy metals in plutonium analyses using a multicollector ICP-MS with a desolvating nebulizer

Analyses of International Atomic Energy Agency (IAEA) and environmental samples for the Pu isotopic content are conducted normally at very low concentrations of Pu—usually in the range of parts per trillion and even more often at the parts per quadrillion level. To analyze such low concentrations, the interferents in the analytical solution must be reduced as much as possible. Polyatomic interferents (PIs), formed by heavy elements (HEs) from Hf to Bi, are known to create problems for Pu isotopic analyses, because even the relatively high resolution of a modern multicollector (MC) inductively coupled plasma-mass spectrometer (ICP-MS) is insufficient to separate Pu isotopes from such PIs in most cases. Desolvating nebulizers (DSNs) (e.g., APEX and AridusII) reduce significantly the formation of PIs compared to the use of wet plasma. The purpose of this work was to investigate the rate of PI formation produced by HMs when a high-resolution (HR) MC-ICP-MS with a DSN was used for Pu isotopic analyses and to estimate the influence of the HEs present in the sample on the results of the analyses. The NU Plasma HR MC and AridusII DSN were used in this investigation. This investigation was done for the interferents for all Pu isotopes normally analyzed by ICP-MS, including 244Pu, with the exception of 238Pu, which most of the time cannot be analyzed using an ICP-MS, because of the overwhelming presence of 238U in the solutions. The PI formation rates were determined and reported. Selected IAEA samples were scanned for the presence of HEs and the influence of HEs on the results of Pu isotopic analyses was evaluated.