The use of time-of-flight static secondary ion mass spectrometry imaging for the molecular characterization of single aerosol surfaces

The imaging feasibility of time-of-flight static secondary ion mass spectrometry (TOF S-SIMS) has been investigated for the identification of the molecular composition of inorganic constituents at the surface of single aerosol particles. Selected test cases involved the study of single ambient aerosol particles (aerodynamic diameter 2–4 μm) collected by cascade impaction and the characterization of laboratory made CaCO3 particles exposed to HNO3 and H2SO4. A methodological optimization of the experiments helped in identifying a proper collection substrate (silicon wafer), the use of a low particle loading and the application of sputter pre-cleaning as essential aspects to record high quality secondary ion images of molecule specific adduct ions (i.e. one or more analyte molecules attached to a stable ion). Correlation of the features in the ion images at different m/z and the knowledge about the systematic trends in the formation of structural ions from inorganic salts allowed the identification of the molecular composition of the constituents in the studied particles.