Ultra-trace determination of plutonium in marine samples using multi-collector inductively coupled plasma mass spectrometry

Abstract

Sources of plutonium isotopes to the marine environment are well defined, both spatially and temporally, which makes Pu a potential tracer for oceanic processes. This paper presents the selection, optimisation and validation of a sample preparation method for the ultra-trace determination of Pu isotopes (Pu-240 and Pu-239) in marine samples by multi-collector (MC) ICP-MS. The method was optimised for the removal of the interference from U-238 and the chemical recovery of Pu. Comparison of various separation strategies using AG1-X8, TEVA, TRU, and UTEVA resins to determine Pu in marine calcium carbonate samples is reported. A combination of anion-exchange (AG1-X8) and extraction chromatography (UTEVA/TRU) was the most suitable, with a radiochemical Pu yield of 87 +/- 5% and a U decontamination factor of 1.2 x 10(4). Validation of the method was accomplished by determining Pu in various IAEA certified marine reference materials. The estimated MC-ICP-MS instrumental limit of detection for Pu-239 and Pu-240 was 0.02 fg mL(-1), with an absolute limit of quantification of 0.11 fg. The proposed method allows the determination of ultra-trace Pu, at femtogram levels, in small size marine samples (e.g., 0.6-2.0 g coral or 15-20 L seawater). Finally, the analytical method was applied to determining historical records of the Pu signature in coral samples from the tropical Northwest Pacific and Pu239+240 concentrations and Pu-240/Pu-239 atom ratios in seawater samples as part of the 2008 GEOTRACES intercalibration exercise. (C) 2010 Elsevier B.V. All rights reserved.