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In order to measure trace plutonium and its isotopes ratio ( 240 Pu/ 239 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 ( 238 U 1 H and 238 UH 2 + ) and tailing of 238 U, but significantly improving the measurement sensitivity of plutonium isotopes by employing NH 3 /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 238 U interference for 239 Pu measurement using NH 3 -He reaction gases was explored to be the formation of UNH + and UNH 2 + in the reactions of UH + and U + with NH 3 , while no reaction between NH 3 and Pu + . The detection limits of this method were estimated to be 0.55 fg mL -1 for 239 Pu, 0.09 fg mL −1 for 240 Pu. The analytical precision and accuracy of the method for Pu isotopes concentration and 240 Pu/ 239 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 239 Pu and 240 Pu concentrations and 240 Pu/ 239 Pu atomic ratios in soil samples collected in coastal areas of eastern China. [ABSTRACT FROM AUTHOR]

To accurately determine ultra-trace Pu isotopes in small environmental samples, we explored ICP-MS/MS in NH 3 –He mode, and investigated mechanism of 238U interference removal and measurement sensitivity improvement for plutonium isotopes. The interference of uranium and uranium hydrides was effectively eliminated using 0.4 mL/min NH 3 as reaction gas by shifting them to U(NH m) n + and UH(NH m) n +. The overall interference of uranium was reduced to <2.4 × 10−7, while remaining excellent 239Pu sensitivity (13,900 Mcps/(mg/L)) mainly due to ion focusing effect of Pu by helium gas. On this basis, the purification of plutonium using a single AG1- × 4 column was proved to be sufficient for accurate determination of plutonium isotopes by the developed detection method, and the detection limits for the method were estimated to be 0.16 fg (0.4 μBq) for 239Pu, 0.046 fg (0.4 μBq) for 240Pu and 0.039 fg (0.15 mBq) for 241Pu. The method was validated by analyzing plutonium isotopes in certificated reference materials and reported environmental samples of only 1–2 g. The analytical results of ultra-trace Pu isotopes in small amounts (∼1 g) of lake sediments obtained by the developed method were successfully applied to sediment dating. [Display omitted] • The overall interference of uranium was reduced to <2.4 × 10−7 by mass-shift mode. • Ion focusing effect of Pu by He gas and KED resulted in excellent Pu sensitivity. • Single AG1- × 4 column is sufficient for accurate measurement of Pu in small samples. • Low detection limits of 0.4 μBq for both 239Pu and 240Pu and 0.15 mBq for 241Pu. • Measured results of ultra-trace Pu isotopes succeed in sediment dating application. [ABSTRACT FROM AUTHOR]