PNNL

Abstract

The analyses of IAEA and environmental samples for Plutonium isotopic content are conducted normally at very low concentrations of Pu - usually in the range of part per trillion level and even more often at the parts per quadrillion level. To analyze such low concentrations, the interferences in the analytical solution must be reduced as much as possible. Polyatomic interferences (PIs), formed by the heavy metals (HMs) from Hf to Bi are known to create the problems for Pu isotopic analyses, because even the relatively high resolution of a modern multicollector ICP-MS is not enough to separate Pu isotopes from this PIs in most of the cases. Desolvating nebulizers (DSN) (e.g. APEX and AridusII) reduce significantly the formation of PIs compare to the use of wet plasma. The purpose of this work was to investigate the rate of formation of PIs, produced by HMs, when high resolution MC ICP-MS with desolvating nebulizer was used for Pu isotopic analyses and to estimate the influence of the metals present in the sample on the results of analyses. The NU Plasma HR Multicollector and AridusII desolvating nebulizer were used in this investigation. This investigation was done for all Pu isotopes normally analyzed by ICP-MS, including 244Pu, with the exception of 238Pu, which most of the time can’t be analyzed by ICP-MS, because of the overwhelming presence of 238U in the solutions. The formation rates were determined and reported for all 12 HMs from Hf to Bi. Selected IAEA samples were scanned for the presence of HMs and the influence of HMs on the results of Pu isotopic analyses was evaluated. It was found that the implemented separation procedure provides sufficient separation of HM from Pu, although the effect of PIs on the measurement of low level isotopes like 241Pu and 242Pu in some cases can still be observed.