Determination of ultra-low level plutonium isotopes (239Pu, 240Pu) in environmental samples with high uranium

Publication date: 1 September 2018
Source:Talanta, Volume 187
Author(s): Shan Xing, Weichao Zhang, Jixin Qiao, Xiaolin Hou
In order to measure trace plutonium and its isotopes ratio (²⁴⁰Pu/²³⁹Pu) 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 (²³⁸U¹H and ²³⁸UH2⁺) and tailing of ²³⁸U, but significantly improving the measurement sensitivity of plutonium isotopes by employing NH3/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 ²³⁸U interference for ²³⁹Pu measurement using NH3-He reaction gases was explored to be the formation of UNH⁺ and UNH2⁺ in the reactions of UH⁺ and U⁺ with NH3, while no reaction between NH3 and Pu⁺. The detection limits of this method were estimated to be 0.55 fg mL^-1 for ²³⁹Pu, 0.09 fg mL⁻¹ for ²⁴⁰Pu. The analytical precision and accuracy of the method for Pu isotopes concentration and ²⁴⁰Pu/²³⁹Pu 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 ²³⁹Pu and ²⁴⁰Pu concentrations and ²⁴⁰Pu/²³⁹Pu atomic ratios in soil samples collected in coastal areas of eastern China.

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