Concurrent determination of 237Np and Pu isotopes using ICP-MS: analysis of NIST environmental matrix standard reference materials 4357, 1646a, and 2702

An optimized method was developed to analyze environmental soil and sediment samples for 237Np, 239Pu, and 240Pu by ICP-MS using a 242Pu isotope dilution standard. The high yield, short time frame required for analysis, and the commercial availability of the 242Pu tracer are significant advantages of the method. Control experiments designed to assess method uncertainty, including variation in inter-element fractionation that occurs during the purification protocol, suggest that the overall precision for measurements of 237Np is typically on the order of ±5%. Measurements of the 237Np concentration in a Peruvian Soil blank (NIST SRM 4355) spiked with a known concentration of 237Np tracer confirmed the accuracy of the method, agreeing well with the expected value. The method has been used to determine neptunium and plutonium concentrations in several environmental matrix standard reference materials available from NIST: SRM 4357 (Radioactivity Standard), SRM 1646a (Estuarine Sediment) and SRM 2702 (Inorganics in Marine Sediment).