Rapid determination of Pu isotopes and atom ratios in small amounts of environmental samples by an on-line sample pre-treatment system and isotope dilution high resolution inductively coupled plasma mass spectrometry

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Abstract
Isotope dilution (ID) high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) combined with an on-line sample pre-treatment method was applied to the trace determination of 239Pu, 240Pu and 240Pu/239Pu ratios in small amounts of environmental samples. To reduce the interference effect of 238U, a microconcentric nebulizer, MCN-6000®, was used as a sample introduction method, which showed a 5-fold lower UH+/U+ ratio than the conventional pneumatic nebulizer. 238U separation and preconcentration of Pu were performed sequentially on two extraction resins, Sr-Spec® and TEVA-Spec®, which were sequentially combined in PrepLabTM, an integrated liquid handing system. By reducing the final sample volume to 2.4 ml, injecting it into the HR-ICP-MS system and employing the MCN-6000, the analysis of Pu isotopes is feasible in 1 g of soil and sediment having the environmental level of Pu. The detection limits for 239Pu, 240Pu and 242Pu by this method were about 4 fg ml−1 (9.2 µBq ml−1), 3 fg ml−1 (25 µBq ml−1) and 6 fg ml−1 (0.87 µBq ml−1), respectively. These represent total amounts of 9.6, 7.2 and 14 fg for 239Pu, 240Pu and 242Pu in a final sample volume. After digestion of the sample, the 238U elimination and Pu preconcentration procedures were fully automated. Sample preparation is therefore far simpler and the full sample analysis process can be achieved within about 5 h. The analytical reliability was confirmed using several certified or standard reference materials (NIST SRM-4350b, IAEA-6, IAEA-300, IAEA-367, IAEA-368, IAEA-375).

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