Determination of plutonium isotopes in seawater reference materials using isotope-dilution ICP-MS

We analyzed the activities of 239Pu, 240Pu, 239+240Pu, 241Pu, the ratio of number of atoms (atom ratio) for 240Pu/239Pu, and the activity ratio of 241Pu/239+240Pu in seawater reference materials, IAEA-443 and IAEA-381, using a highly sensitive isotope dilution sector field inductively coupled plasma mass spectrometry method. With a mean chemical yield of 65 % determined with 242Pu as a tracer, we found that the experimentally established values in IAEA-443 for 239Pu, 240Pu, 241Pu and 239+240Pu activities are almost the same as those in IAEA-381. Regarding the 239+240Pu activity, we provided the most precise and accurate result among the twelve laboratories which participated in the interlaboratory comparison. In addition, for the 240Pu/239Pu atom ratio, our results for IAEA-381 (0.2315 +/- 0.0008) and IAEA-443 (0.2325 +/- 0.0008) are in good agreement with the IAEA information value (0.229 +/- 0.006), but have much smaller uncertainty. Since the new seawater reference material, IAEA-443, is commercially available, it can be used not only for method validation for seawater plutonium isotope ratio and activity analysis, but also for more general use as a plutonium isotope standard for mass discrimination correction for other environmental samples