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

237Np, 239Pu and 240Pu are radionuclides which have radiological and chemical toxicity and long half-lives. To study the environmental distribution and behaviors of 237Np and Pu isotopes, the reliable determination of these radionuclides in environmental samples is required. This work presents a method developed for simultaneous analysis of ultra-trace level 237Np and Pu isotopes in soil and sediment samples by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). 242Pu was used as a yield tracer for 237Np as well as for Pu isotopes. A single chromatographic column packed with anion exchange resin (AG MP-1M) was used for the separation of 237Np and Pu isotopes from the matrix elements and other potential interferences. The use of a single resin column is advantageous since it simplifies the separation procedure, thus reducing the possibility of chemical fractionation between 237Np and the non-isotopic 242Pu tracer. The SF-ICP-MS measurement precision of the 237Np/242Pu atom ratio for sub-fg/mL level 237Np and 242Pu was 0.97%, and the overall fractionation between 237Np and 242Pu for the whole analysis procedure was 1.010±0.038. Besides, the removal of U which was the primary interference for both 237Np and Pu isotopes measurement was efficient although only single resin column was employed. The decontamination factor of U was 1.8×106 to 1.7×107, and that ensured the interference effect of 238U to the 237Np, 239Pu and 240Pu measurements was negligible or could be easily corrected. Four standard reference materials were analyzed to check the reliability of this method and the concentrations of 237Np and Pu isotopes determined agreed well with the certificated or reported values, illustrating 242Pu was an effective non-isotopic tracer for 237Np determination. Finally, the developed method was successfully employed in the analysis of the global fallout level of 237Np and Pu isotopes in Japanese paddy soil samples to study their environmental behaviors