High-Performance Method for Determination of Pu Isotopes in Soil and Sediment Samples by Sector Field-Inductively Coupled Plasma Mass Spectrometry

Abstract

Plutonium is extensively studied in radioecology (e.g., soil to plant transfer and radiological assessment) and geochemistry (e.g., sediment dating). Here, we reported a new chemical separation method for rapid determination of Pu in soil and sediment samples, based on the following investigations: extraction behaviors of interfering elements (IEs, for inductively coupled plasma mass spectrometry (ICPMS) measurement) on TEVA resin; decontamination of U using TEVA, UTEVA, and DGA resins; and the impact of coprecipitation on Pu determination. The developed method consists of four steps: HNO₃ leaching for Pu release; CaF₂/LaF₃ coprecipitation for the removal of major metals and U; the proposed TEVA + UTEVA + DGA procedure for the removal of U, Pb, Bi, Tl, Hg, Hf, Pt, and Dy; and ICPMS measurement. The accuracy of this method in determining ^239+240Pu activity and ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu isotopic ratios was validated by analyzing five standard reference materials (soil, fresh water sediment, and ocean sediment). This method is characterized by its stable and high Pu recovery (90-97% for soil; 92-98% for sediment) and high decontamination factor of U (1.6 × 10⁷), which is the highest reported for soil and sediment samples. In addition, the short analytical time of 12 h and the method detection limits, which are the lowest yet reported in literature, of 0.56 μBq g^-1 (0.24 fg g^-1) for ²³⁹Pu, 1.2 μBq g^-1 (0.14 fg g^-1) for ²⁴⁰Pu, and 0.34 mBq g^-1 (0.09 fg g^-1) for ²⁴¹Pu (calculated on the basis of a 1 g soil sample) allow the rapid determination of ultratrace level Pu in soil and sediment samples.