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

In order to measure trace plutonium and its isotopes ratio (Pu-240/Pu-239) 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)-U-238-H-1 and (UH2+)-U-238) and tailing of U-238, 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 U-238 interference for (PU)-P-239 measurement using NH3-He reaction gases was explored to be the formation of UNI+ 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 (PU)-P-239, 0.09 fg for Pu-240. The analytical precision and accuracy of the method for Pu isotopes concentration and Pu-240/ Pu-239 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-239 and Pu-240 concentrations and Pu-240/Pu-239 atomic ratios in soil samples collected in coastal areas of eastern China