Results from the Zurich sea water (ZSW) intercomparison study for U- and Pu-isotopes

Approximately 350L of sea water samples were collected to prepare a large volume (Zurich Sea Water, ZSW) intercomparison sample for 236 U and other actinides. Here we report the results of the intercomparison study for U- and Pu-isotopes. ZSW was processed in six different chemistry labs and measured on five AMS systems and one MC-ICP-MS system, respectively. The analysis of the reported U-isotopic data shows that the scatter, indicated by the one sigma uncertainty for a single measurement, of the 236 U/ 238 U ratios and the 236, 238 U-concentrations is 5 % and 3 %, respectively. A Chi-squared analysis shows that the external error (lab-scatter) is 1–2 % and 3 % for the 236, 238 U-concentrations and the 236 U/ 238 U ratios, respectively. The fact that ZSW has been characterized by many different (A)MS labs makes it a valuable internal standard for quality control for the analysis of anthropogenic U- and Pu-isotopes in seawater.