[en] Direct-inlet mass spectrometry is a method for analysis of individual particles without manually locating and isolating them. In this method, particles entrained in air are admitted directly into the ion source of a surface-ionization mass spectrometer. Although the method has so far been considered only for the real-time analysis of airborne particles, it also has potential for the analysis of particles in collected samples. For the latter application, the particles would be resuspended from a collecting medium and introduced into the direct-inlet mass spectrometer. Both micrometer and submicrometer particles would be analyzed. The isotopic composition of the uranium or plutonium contained in each individual particle would be measured. 6 figures