Determination of ultra-low level plutonium isotopes (Pu, Pu) in environmental samples with high uranium.

In order to measure trace plutonium and its isotopes ratio (Pu/Pu) in environmental samples with a high uranium, an analytical method was developed using radiochemical separation for separation of plutonium from matrix and interfering elements including most of uranium and ICP-MS for measurement of plutonium isotopes. A novel measurement method was established for extensively removing the isobaric interference from uranium (UH and UH) and tailing of U, but significantly improving the measurement sensitivity of plutonium isotopes by employing NH/He as collision/reaction cell gases and MS/MS system in the triple quadrupole ICP-MS instrument. The results show that removal efficiency of uranium interference was improved by more than 15 times, and the sensitivity of plutonium isotopes was increased by a factor of more than 3 compared to the conventional ICP-MS. The mechanism on the effective suppress of U interference for Pu measurement using NH-He reaction gases was explored to be the formation of UNH and UNH in the reactions of UH and U with NH, while no reaction between NH and Pu. The detection limits of this method were estimated to be 0.55 fg mL for Pu, 0.09 fg mL for Pu. The analytical precision and accuracy of the method for Pu isotopes concentration and Pu/Pu atomic ratio were evaluated by analysis of sediment reference materials (IAEA-385 and IAEA-412) with different levels of plutonium and uranium. The developed method were successfully applied to determine Pu and Pu concentrations and Pu/Pu atomic ratios in soil samples collected in coastal areas of eastern China.