AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Extractive Electrospray Ionisation (EESI): A Novel Mass Spectrometry Technique for the Online Characterization of Organic Aerosol
PETER GALLIMORE, Markus Kalberer, University of Cambridge
Abstract Number: 381 Working Group: Instrumentation and Methods
Abstract Organic compounds are often the dominant fraction of tropospheric aerosol. Despite this, our understanding of the composition of organic aerosol is limited. A lack of detailed knowledge of the chemical composition of aerosols limits our understanding of their effect on climate and air quality.
We present a new technique for online measurement of the compounds present in organic aerosol: Extractive Electrospray Ionization (EESI) coupled to Mass Spectrometry (MS). In this method, a plume of charged solvent droplets is generated using an Electrospray Ionisation (ESI) source. Aerosol particles are directed into this spray and particle-into-droplet extraction occurs, dissolving the soluble aerosol components. The volatile solvent evaporates and gas-phase aerosol analyte ions are formed and sampled at the MS inlet. We present here a custom-designed EESI source which has been designed and optimized to interface with a commercial Ultra-High Resolution Mass Spectrometer.
EESI-MS offers a number of advantages: The online ionization mechanism provides composition information on aerosols in flow-tube and chamber studies with a time resolution of seconds, without the potentially large sampling artefacts introduced by collecting aerosols onto substrates for offline analysis. The ionization process produces molecular ions with minimal fragmentation, which greatly aids the interpretation of spectra for complex mixtures.
We have demonstrated high sensitivity for aerosols composed of oxidized organic compounds. For example, tartaric acid aerosol can be detected at mass concentrations below 0.1 micrograms per cubic meter, with a dynamic range of about 3.5 orders of magnitude, using tandem MS experiments.
EESI can be used for detailed aerosol composition studies and elucidation of particle-phase reaction kinetics. Time-resolved measurements of ozonolysis reaction products of oleic acid aerosol show the formation of oligomers. The average length and oxygen:carbon ratio of these oligomers increase with reaction time, which has implications for particle viscosity, hygroscopicity and phase.