Uranium isotope analysis of particles using particle-inlet mass spectrometry

There is considerable interest in developing methods to measure uranium isotopes in environmental samples, both for nuclear nonproliferation purposes and for environmental monitoring near nuclear facilities. Trace levels of anthropogenic uranium can be difficult to detect in bulk environmental samples due to relatively abundant natural uranium, which can occur in concentrations exceeding 1 ppm. An alternative is to analyze single particles isolated from the bulk sample. Particle analysis offers enhanced sensitivity and selectivity compared to bulk analysis because anthropogenic uranium often occurs as micron-sized uranium oxide particles, which can be separated and individually analyzed. The authors have developed a mass spectrometric method for measuring the isotopic composition of individual particles in heterogeneous particulate samples without having to isolate them from the sample. The technique, called particle-inlet mass spectrometry (PIMS), analyzes the elemental or isotopic composition of particles by directly admitting them in aerosol form into a mass spectrometer. The PIMS technique is rapid: Particulate samples, such as soils, can be measured in minutes, and airborne particles, such as dusts, can be measured in real time. The PIMS technique is highly sensitive: uranium isotopes can be measured in micron-sized UO2 particles that contain ≤10-11 g of uranium