A novel strategy for Pu determination in water samples by automated separation in combination with direct ICP-MS/MS measurement.

ABSTRACT

Methods for Pu determination in water samples has been longtime studied but they generally involved tedious manual operations. In this context, we proposed a novel strategy for accurate determination of ultra-trace Pu in water samples by the combination of fully automated separation with direct ICP-MS/MS measurement. A recently commercialized extraction resin TK200 was used for single-column separation due to its distinctive nature. Acidified waters up to 1 L were directly loaded to the resin at high flow rate (15 mL min-1) with omitting the frequently used co-precipitation process. Small volumes of dilute HNO3 were used for column washing, and Pu was efficiently eluted within only 2 mL 0.5 mol L-1 HCl-0.1 mol L-1 HF with a stable recovery (65%). This separation procedure was fully automated under the control of user program, meanwhile the final eluent was compatible for direct ICP-MS/MS measurement without extra sample treatment. In that way, both the labor intensity and reagent consumption were minimized compared with existing methods. With the high decontamination (104 to 105) of U in the chemical separation and the further elimination of uranium hydrides under oxygen reaction model during ICP-MS/MS measurement, the overall interference yields of UH+/U+ and UH2+/U+ were down to 10-15. The limits of detection (LODs) of this method reached 0.32 µBq L-1 for 239Pu and 2.00 µBq L-1 for 240Pu, which were much lower than those stipulated in the general guidelines for drinking water standards, suggesting this method was promising in routine or emergency radiation monitoring. Furthermore, the established method was successfully applied in a pilot study to determine global fallout derived Pu in surface glacier samples with extremely low concentrations of 239+240Pu, which suggested the method would also be feasible in glacial chronology studies in the future.