Analysis of ultrafine metal oxide particles in aerosols using mobility-resolved time-of-flight mass spectrometry

Abstract

In this work we present a powerful method to gain insight into the formation of inorganic nanoparticles from the gas phase by combining a high-resolution differential mobility analyzer with a time-of-flight mass spectrometer. Exemplary particles are generated by glowing-wire evaporation from tungsten, tantalum, rhenium, niobium and molybdenum and transferred via a new custom-made interface to the mobility classifier that is directly attached to the mass spectrometer. With only minor fragmentation occurring, clusters that represent early stages of particle formation from the gas phase can be detected. Regardless of the inert experimental conditions, only oxides were found for all tested precursor metals. Comparing the recorded mass-mobility data with theoretical predictions from a modified Mason-Schamp equation shows that produced materials possess densities smaller than those of the respective bulk materials. The maximum observed particle sizes were about 2 nm.