Simultaneous analysis of 237Np and Pu isotopes in environmental samples by ICP-SF-MS coupled with automated sequential injection system

Abstract

A simultaneous analytical method for ²³⁷Np, ²³⁹Pu and ²⁴⁰Pu has been developed using sector field inductively coupled plasma mass spectrometry (ICP-SF-MS) detection combined with an automated sequential injection (SI) separation system. The chemical purification of these actinides was carried out on an actinide-specific extraction chromatographic resin, TEVA-Spec, in an automated SI system. The similar chemical behaviors of Np and Pu on TEVA-Spec was confirmed by recovery test after treating with ascorbic acid in 5 M HNO₃. TEVA-Spec maintained its re-usability, giving high and consistent chemical recovery, and showed good selectivity for Np and Pu and a low memory effect during the consecutive analysis of nine replicate samples. The high chemical recovery (>90%), reliable accuracy and repeatability of ²³⁷Np and Pu isotope purification using the SI system were proved using standard reference materials. Low detection limits of 2.5, 2.1 and 0.42 fg ml⁻¹ were obtained for ²³⁷Np, ²³⁹Pu and ²⁴⁰Pu, respectively, which make it possible to analyze these nuclides in samples of soil and sediment as low as 1 g. With the exception of the preparation process required prior to loading a sample, all chemical purifications were carried out automatically by the programmed SI system, and were completed within 1 hour, which included measurement by ICP-SF-MS. This method was successfully applied to the analysis of the environmental levels of ²³⁷Np and Pu in soil, sediment and in biological samples.