Ultra-Trace Analysis of Fallout Plutonium Isotopes in Soil: Emerging Trends and Future Perspectives

Abstract

The measurement of isotopic abundances and ratio variations of plutonium can provide important information about the sources and behaviours of radiogenic isotopes in the environment. The detection of ultra-trace isotopes of plutonium is increasing interest in the scientific literature for the determination of soil erosion rates due to their long retention times in the environment. The characteristics of plutonium within the environment make it an ideal tracer for the determination of soil redistribution rates and its robustness presents the opportunity to replace more commonly used radioisotopes such as 137Cesium and 210Lead. However, ultra-trace analysis of plutonium (fg g−1) presents analytical challenges which must be overcome in a variety of soil types. Inductively Coupled Plasma Mass Spectrometry has proven valuable for detection of plutonium in a range of environmental samples. However, severe polyatomic interferences from uranium isotopes significantly limits its application. Due to the improvements in detection sensitivity and reaction cell technology, inductively coupled plasma tandem mass spectrometry, which is also commonly referred to as triple quadrupole inductively coupled plasma tandem mass spectrometry (ICP-MS/MS), has emerged as an exceptional tool for ultra-trace elemental analysis of plutonium isotopes in environmental samples overcoming the limitations of standard quadrupole ICP-MS such as limited sensitivity and cost of analysis. In this review, common methods reported in the literature for the separation and subsequent detection of plutonium isotopes are compared to recent advances in analysis using ICP-MS/MS technology. Graphical Abstract

Optimisation of plutonium separations using TEVA cartridges and ICP-MS/MS analysis for applicability to large-scale studies in tropical soils

“…[7][8][9][10] In recent years, ICP-MS has gained popularity due to its low detection limits, short analytical time, high sample throughput, relatively simple operation, and lower instrument cost. 5,[11][12][13][14] Despite the benets of ICP-MS, the technique is severely constrained by polyatomic interferences, most notably uranium hydrides (UH + ). In addition, 238 U tailing interferes with the detection of mass-to-charge ratio (m/z) 239 due to its concentration being several orders of magnitude greater than that of 239 Pu in soils.…”

“…This method is increasingly utilised for the determination of Pu isotopes due to its enhanced abundance sensitivity, which effectively eliminates the interference of the 238 U peak tailing on the measurement of 239 Pu and 240 Pu. 7,8,14,22 In addition, the main interference of 238 UH + on 239 Pu can be eliminated by utilising different reaction gases in the collision-reaction cell. 4,7,8,10,15,23 The quadrupole mass lter positioned in front of the collision-reaction cell permits the pre-selection of species, thereby enhancing the reaction efficiency of the collision cell and prohibiting the formation of secondary polyatomic interference.…”