Organosulfates - A new component of humic-like substances in atmospheric aerosols?

Ion trap mass spectrometry (ITMS) was used to obtain further qualitative information about the chemical composition of humic-like substances (HULIS) in atmospheric particulate matter. Particles <= 10 mu m (PM10) were collected on quartz fiber filters for 24 h in the region of Basel (Switzerland) and extracted with water. HULIS were separated from inorganic salts by size exclusion chromatography (SEC) and detected by electrospray ionization in the negative ion mode (ESI(-)). Series of consecutive fragment ion spectra (MSn) were recorded by ITMS. Full scan mass spectra of the extracts showed a mass distribution pattern characteristic for HULIS. Different molecular ions were selected from this pattern for further fragmentations. Among them the molecular ion m/z 299 was considered as representative and intensively studied. Many MS2 and MS3 fragment spectra contained a fragment m/z 97 and a neutral loss of 80 u. Time-of-flight (TOF) MS and deuterium exchange experiments identified m/z 97 as hydrogen sulfate. MS2 and MS3 fragment spectra supported the existence of sulfate covalently bound to HULIS. The fragmentation behavior of sulfated HULIS could be confirmed by model compounds.