A new milestone for ultra-low 236U/238U isotope ratio measurements by ICP-MS/MS

Abstract

Uranium isotope composition in environmental samples allows to trace its origin. Therefore, the analytical community has been working for several years to reduce the detection limit of the ²³⁶U/²³⁸U isotopic ratio using mass spectrometry, and in particular the ICP-MS/MS technology. The latest generation of ICP-MS/MS, recently commercialized, has improved performance, including better ion transmissions and an extended dynamic range of mass detection. These improvements, the coupling with an efficient desolvating module and the addition of oxygen in the collision/reaction cell permitted to remove the interferences of ²³⁶U⁺ ion measurements (abundance sensitivity of the major isotopes and polyatomic interferences, notably ²³⁵UH⁺ ions). For the first time a precise determination of the ²³⁶U/²³⁸U isotopic ratio up to 10⁻¹¹ was demonstrated, validated by the analysis of certified reference materials and environmental samples previously measured by AMS. This new limit is a new milestone in the determination of ultra-low ²³⁶U/²³⁸U isotope ratios and opens the way to various geochemical applications.