Development of a hydrophilic interaction liquid chromatography (HILIC) method for the chemical characterization of water-soluble isoprene epoxydiol (IEPOX)-derived secondary organic aerosol

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, methyltetrol sulfates, and oligomers thereof in atmospheric fine particulate matter (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 electrospray ionization high-resolution mass spectrometry (RPLC/ESI-HR-MS). However, both techniques have limitations in explicitly resolving and quantifying polar SOA constituents due either to thermal degradation or poor separation. With authentic 2-methyltetrol and methyltetrol sulfate standards synthesized in-house, we developed a hydrophilic interaction liquid chromatography (HILIC)/ESI-HR-quadrupole time-of-flight mass spectrometry (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-Methyltetrols were simultaneously resolved along with 4-6 diastereomers of methyltetrol sulfate, allowing efficient quantification of both major classes of SOA constituents by a single non-thermal analytical method. The sum of 2-methyltetrols and methyltetrol sulfates accounted for approximately 92%, 62%, and 21% 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 methyltetrol sulfates was 171-271% the mass concentration of methyltetrol. Mass concentrations of methyltetrol sulfates were 0.39 and 2.33 μg m-3 in a PM2.5 sample collected from central Amazonia and the southeastern U.S., respectively. The improved resolution clearly reveals isomeric patterns specific to methyltetrol sulfates from acid-catalyzed multiphase chemistry of β- and δ-IEPOX. We also demonstrate that conventional GC/EI-MS analyses overestimate 2-methyltetrols by up to 188%, resulting (in part) from the thermal degradation of methyltetrol sulfates. Lastly, C5-alkene triols and 3-methyltetrahydrofuran-3,4-diols are found to be largely GC/EI-MS artifacts formed from thermal degradation of 2-methyltetrol sulfates and 3-methyletrol sulfates, respectively, and are not detected with HILIC/ESI-HR-QTOFMS.

Chemical composition of isoprene SOA under acidic and non-acidic conditions: effect of relative humidity

“…Silylation of polar compounds results in reduced polarity, enhanced volatility, and increased thermal stability, and they enable the GC-MS analysis of many compounds otherwise involatile or too unstable for these techniques. Therefore, appropriate caution should be taken, for example, with desulfation reactions associated with primary organosulfates (Takano et al, 1992;Kolender et al, 2004;Bedini et al, 2016Bedini et al, , 2017Cui et al, 2018), and corrections might be warranted when analyzing methyltetrols.…”

“…The presence of 2-methyltetrols and 2methylglyceric acid and their sulfated analogues in isoprene SOA at a wide range of RH conditions suggests that SOA water content does not significantly affect their formation. Early chamber studies on isoprene ozonolysis by Jang et al (2002) and Czoschke et al (2003) showed enhanced SOA yields in the presence of acidified aerosol seeds. Recent laboratory results showed that the acidity of aerosol seeds plays a major role in the reactive uptake of isoprene oxidation products by particle phases (Paulot et al, 2009;Surratt et al, 2010;Lin et al, 2012;Gaston et al, 2014a, b;Riedel et al, 2015).…”

“…An enhancement of isoprene (ISO)-SOA yields is controlled by various factors including NO x concentration Chan et al, 2010;Surratt et al, 2006Surratt et al, , 2010 and the acidity of preexisting aerosol (Jang et al, 2002;Czoschke et al, 2003;Edney et al, 2005;Kleindienst et al, 2006;Surratt et al, 2007aSurratt et al, , 2010Jaoui et al, 2010;Szmigielski et al, 2010). The strength of the acidity depends on the aerosol liquid water content and the relative humidity (RH; Nguyen et al, 2011;Zhang et al, 2011;Lewandowski et al, 2015;Wong et al, 2015), which are coupled.…”

Impact of anthropogenic emissions on biogenic secondary organic aerosol: observation in the Pearl River Delta, southern China

“…Due to the lack of authentic standards, surrogate standards were used to quantify BSOA tracers except PNA. Specifically, erythritol, PNA, and octadecanoic acid were used for the quantification of SOA I tracers (Ding et al, 2008), other SOA M tracers , and CA , respectively. The method detection limits (MDLs) for erythritol, PNA, and octadecanoic acid were 0.01, 0.02, and 0.02 ng m −3 , respectively.…”

Quantification of known and unknown terpenoid organosulfates in PM10 using untargeted LC–HRMS/MS: contrasting summertime rural Germany and the North China Plain

“…Nonetheless, more recent studies have shown that, in particular, the application of new developments in separation techniques, such as hydrophilic interaction LC (also referred to as HILIC), can substantially increase the number of detectable isoprene OS and facilitate their identification and quantification (Cui et al 2018;Hettiyadura et al 2015Hettiyadura et al , 2017Hettiyadura et al , 2019.…”