Uranium isotopic analysis in unpurified solutions by ICP-MS

Abstract

Mass spectrometry is a widely used tool for analysis of uranium isotopic composition. For solution based inductively coupled plasma mass spectrometry, uranium isotopes are typically analyzed after purification from complex matrices. In this work, we tested the ability of three mass spectrometers (ThermoScientific iCAP TQ, ThermoScientific Neoma, and Agilent 8900) to analyze uranium isotopes in an unpurified NIST reference material (SRM2780a, Hard Rock Mine Waste) digest solution. Results indicate that ²³⁵U/²³⁸U can be analyzed within 1% of the true value. ²³⁴U/²³⁸U is a more challenging analysis due to low count rates and potential isobar interferences, but strategies to mitigate these effects, such as the use of reaction gases in a collision cell and desolvating nebulizer introduction system, are effective for the triple quadrupole instruments. However, the use of the Neoma MS/MS in reaction mode using O₂ gas was problematic. Nevertheless, analysis of unpurified solutions for quick assessment of uranium isotope compositions is practical, especially when high precision is not required.