10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Ultrahigh Resolution Orbitrap Elite Mass Spectrometry Reveals Unprecedented Molecular Detail in Atmospheric Aerosol
LYNN MAZZOLENI, Simeon Schum, Matthew Brege, Tyler Leverton, Elizabeth Rose, Maryam Khaksari, Michigan Technological University
Abstract Number: 1618 Working Group: Instrumentation
Abstract Atmospheric organic aerosol is a very complex mixture containing components ranging from hydrophobic condensed aromatics to highly oxidized molecules. The compounds include C, H, N, O, and S, where N and S can exist in either oxidized or reduced forms. Ionization methods control what type of molecules are introduced into a mass spectrometer, thus a variety of ionization methods can be used for an accurate assessment of the overall organic aerosol composition. Specifically, the combination of electrospray ionization and atmospheric pressure photoionization is ideal for widespread coverage. Identification of unambiguous molecular formulas for accurate mass measurements requires low measurement error and sufficient mass resolution to separate common isobars. One of the commonly observed isobars in atmospheric aerosol involves molecular formulas that differ by 3.4 mDa due to the exact mass difference of C3 vs. SH4.
The ultrahigh resolving power of the second-generation high field Orbitrap Elite mass spectrometer (R = 240,000 at m/z 400) is sufficient for separation of common aerosol compositional isobars up to ~ 500 Da permitting an accurate assessment of S-containing compounds. The accurate mass measurements of the Orbitrap Elite can be further improved using a combination of custom internal and external calibration methods to refine the assignment of unambiguous molecular formulas. This is especially critical for compositions that include N and S, since the number of possible equivocal molecular formulas increases with increasing molecular weight. Thus, accurate mass measurements with less than 1 ppm mass error are needed to reduce the equivocal formulas.
In this presentation, we will demonstrate the power of ultrahigh resolution Orbitrap Elite mass spectrometry (MS) measurements with a focus on new ionization methods that provide new insights on the detailed molecular composition of ambient organic aerosol. We also present unprecedented molecular complexity using a segmented scanning approach with ultrahigh resolution MS/MS. These results suggest that a wide range of components from hydrophobic condensed aromatics to highly oxidized molecules are present in the aqueous extracts of organic aerosol. A more thorough understanding of organic aerosol composition is vital for an improved estimation of aerosol properties and studies involving fate and transport of pollutants.