Extractive Electrospray Ionization Mass Spectrometry (EESI-MS) is a relatively new technique used for direct, real time analysis of gases, liquids, solids and aerosols with little to no sample preparation. Unlike ESI-MS, EESI-MS involves the interaction of charged electrospray droplets with a separate flow of particles containing the analyte of interest. The probe depth of the analyte particles by interaction with the charged electrospray droplets defines the quantitative and qualitative properties of the EESI mass spectra. Previous studies on EESI-MS indicate either complete coalescence of the analyte particles with the electrospray droplets, or an interaction with a temporal and hence depth dependence, contingent upon the sample and electrospray solvent used. In this study, model components of atmospherically important secondary organic aerosols (SOA) were studied using EESI-MS. The behavior of EESI-MS toward SOA was probed by coating NaCl particles with various thicknesses of organic diacids. Results indicate that the signal strength depends on the solubility of the organic acid in the electrospray solvent, in agreement with previous studies, and also that the outer 10-15 nm of the particles are most susceptible to extraction into the electrospray droplets. To get more insight into the mechanism of EESI-MS, the particles were also studied using aerosol mass spectrometry (AMS), which typically samples the entire particle composition. Results of this study, combined with the EESI-MS results, suggest that the mass spectra obtained with EESI will not necessarily reflect the overall particle composition, especially for particles that are spatially inhomogeneous. However, an advantage of EESI-MS is that it can be tuned through the choice of solvent to emphasize the surface composition of atmospherically important aerosol particles.

Understanding the mechanism of extractive electrospray ionization mass spectrometry for analyzing model secondary organic aerosols

251st National Meeting (2016)

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