Simultaneous determination of ultra-trace level 237Np and Pu isotopes in soil and sediment samples by SF-ICP-MS with a single column chromatographic separation

This work presents a method developed for simultaneous analysis of ultra-trace level Np-237 and Pu isotopes in soil and sediment samples by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). Pu-242 was used as a yield tracer for Np-237 as well as for Pu isotopes. A simple single chromatographic column packed with anion exchange resin (AG MP-1M) was used for the separation of Np-237 and Pu isotopes from the matrix elements and other potential interferences. The SF-ICP-MS measurement precision of the Np-237/Pu-242 atom ratio for sub-fg/mL level Np-237 and (PU)-P-242 was 0.97%, and the overall fractionation between Np-237 and (PU)-P-242 for the whole analysis procedure was 1.010 +/- 0.038. Besides, the single column chromatographic separation realized high decontamination factor of U (1.8 x 10(6) to 1.7 x 10(7)), and that ensured the interference effect of U-238 to the Np-237, Pu-239 and Pu-240 measurements was negligible or could be easily corrected. Four standard reference materials were analyzed for method validation, and the results illustrated Pu-242 was an effective non-isotopic tracer for Np-237 determination. Finally, the developed method was successfully employed in the analysis of the global fallout level of Np-237 and Pu isotopes in Japanese paddy soil samples to study their environmental behaviors.