Reliable determination of 237Np in environmental solid samples using 242Pu as a potential tracer

This paper reports an analytical method for rapid determination of neptunium (Np-237) in environmental solid samples exploiting automated sequential injection (SI)-based anion exchange separation. Pivotal issues on analytical method performance were investigated including sorption behavior of Np-237 onto various AG 1-type anion exchangers; suitability of Pu-242 as a tracer for Np-237 determination in environmental solid samples; and long-term chemical stability of tetravalent Np. Experimental results revealed that the degree of resin cross-linking has a significant influence on the separation efficiency in terms of chemical yields of Np-237 and removal of interfering nuclides. Although ca. 30% of sorbed Np onto AG 1-x 4 was stripped out during HCl rinsing step for the removal of Th, chemical yield ratios of Np-237 to Pu-242 were proven steady with an average value of 0.67 +/- 0.04 (n = 15) under selected experimental conditions. Disulfite-8 M HNO3 was selected as a redox pair for valence adjustment to Np(IV) and the tetravalent Np in the sample solution was demonstrated to be stabilized for up to 5 days under 3 degrees C. The analytical results for reference materials showed a good agreement with the expected values, thereby demonstrating the usefulness of Pu-242 as a non-isotopic tracer for Np-237 chemical yield monitoring. The on-column separation procedure fosters rapid analysis as required in emergency situations since each individual sample can be handled within 2.5 h, and leads to a significant decrease in labor intensity compared to conventional batch-wise protocols. (C) 2011 Elsevier B.V. All rights reserved.