Explicit Mass Spectrometric Determination of Isoprene Epoxydiol (IEPOX)-Derived Secondary Organic Aerosol with a Developed Hydrophilic Interaction Liquid Chromatography (HILIC) Method
Abstract
Acid-catalyzed multiphase chemistry of isoprene epoxydiols (IEPOX) on sulfate aerosol produces substantial amounts of water-soluble secondary organic aerosol (SOA) constituents, including 2-methyltetrols (2-MTs), methyltetrol sulfates (MTSs), and oligomers thereof in atmospheric PM2.5. These constituents have commonly been measured by gas chromatography interfaced to electron ionization mass spectrometry (GC/EI-MS) with prior derivatization, or by reverse-phase liquid chromatography interfaced to mass spectrometry. However, both techniques have limitations in explicitly resolving and quantifying polar SOA constituents due either to thermal degradation or poor separation. With authentic 2-MT and MTS standards synthesized in-house, we developed a hydrophilic interaction liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS) protocol that can chromatographically resolve and accurately measure the major IEPOX-derived SOA constituents in both laboratory-generated SOA and atmospheric PM2.5. 2-MTs were simultaneously resolved with 4-6 isomers of MTS, allowing efficient quantification of both major classes of SOA constituents by a single non-thermal analytical method. The sum of 2-MTs and MTSs accounted for 92±16%, 62±10%, and 21±4% of the laboratory-generated β-IEPOX aerosol mass, laboratory-generated δ-IEPOX aerosol mass, and organic aerosol mass in the southeastern U.S., respectively, where the mass concentration of MTSs were 171-271% the mass concentration of 2-MTs. Notably, improved resolution clearly reveals isomeric patterns specific to MTSs from acid-catalyzed multiphase chemistry of β- and δ-IEPOX. We also demonstrate that conventional GC/EI-MS analyses overestimate 2-MTs by up to 188%, resulting (in part) from the thermal degradation of MTSs. Lastly, C5-alkene triols and 3-methyltetrahydrofuran-3,4-diols are found to be GC/EI-MS artifacts primarily formed from thermal degradation of 2- and 3-MTSs, respectively, and are not detected with the method. Our developed HILIC/ESI-HR-QTOFMS technique can be utilized for explicitly characterizing broader classes of water-soluble SOA constituents and provide greater accuracy and confidence in atmospheric model predictions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A43D..02C
- Keywords:
-
- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0340 Middle atmosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0394 Instruments and techniques;
- ATMOSPHERIC COMPOSITION AND STRUCTURE