Ionization of Gas-Phase Polycyclic Aromatic Hydrocarbons in Electrospray Ionization Coupled with Gas Chromatography

Abstract

Herein, gas-phase polycyclic aromatic hydrocarbons (PAHs) as nonpolar compounds were ionized to protonated molecular ions [M + H] without radical cations and simultaneously analyzed using gas chromatography (GC)/electrospray ionization (ESI)-tandem mass spectrometry (MS/MS). The ionization profile, dissociation, and sensitivity were first investigated to understand the significant behavior of gas-phase PAHs under ESI. The formation of protonated molecular ions of PAHs was distinguished according to the analyte phase and ESI spray solvents. The protonated PAHs exhibited characteristic dissociations, such as H-loss, H-loss, and acetylene-loss, via competition of internal energy. In addition, GC/ESI-MS/MS resulted in relatively lower concentration levels (better sensitivity) for the limits-of-detection (LODs) of PAHs than liquid chromatography (LC)/ESI-MS/MS, and it seems to result from the characteristic ionization mechanism of the gas-phase analyte under ESI. Furthermore, the LODs of gas-phase PAHs depended on molecular weight and proton affinity (PA). Consequently, we demonstrated the relationship among the analyte phases, sensitivities, and structural characteristics (molecular weight and PA) under ESI. The gas-phase PAHs provided enhanced protonation efficiency and sensitivity using GC/ESI-MS/MS, as their molecular weight and PA increased. Based on these results, we offered important information regarding the behavior of gas-phase analytes under ESI. Therefore, the present GC/ESI-MS/MS method has potential as an alternative method for simultaneous analysis of PAHs.

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

“…Various PAHs (17-25, Table 1) were observed in only ceanothus, chamise, and sagebrush BBOA. PAHs in Table 1 are detected from positive ion mode ESI, and although positive mode ESI is not optimal for observing PAHs, larger PAHs are still detectable by this method (Cha et al, 2018). The same PAHs were previously observed by Lin et al (2018) for sagebrush using atmospheric pressure photoionization (APPI) coupled with HPLC-PDA-HRMS, which is more sensitive for the detection of nonpolar aromatic compounds.…”

“…Tar balls are largely externally mixed spheres or spherical aggregates produced from smoldering combustion or through multiphase secondary chemistry (Sedlacek et al, 2018;Tóth et al, 2014). In terms of their chemical composition, tar balls are thought be comprised primarily of oxygenated organic compounds, similar to that of BBOA (Chakrabarty et al, 2010;Girotto et al, 2018;Pósfai et al, 2004;Sedlacek et al, 2018).…”

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

“…Various PAHs (17-25, Table 1) were observed in only ceanothus, chamise, and sagebrush BBOA particles. PAHs in Table 1 are detected from positive ion mode ESI, and although positive mode ESI is not optimal for observing PAHs, larger PAHs are detectable by this method (Cha et al, 2018). The same PAHs were previously observed by Lin et al, 2018 for sagebrush using atmospheric pressure photoionization (APPI) coupled with HPLC/PDA/HRMS, which is more sensitive for the detection of non-polar aromatic 325 compounds.…”

Nontargeted Screening Using Gas Chromatography–Atmospheric Pressure Ionization Mass Spectrometry: Recent Trends and Emerging Potential

“…Similarly, in extractive electrospray ionization (EESI), the charged droplets collide with and ionize a secondary aerosol spray. In principle, the same approach could be used to ionize gaseous molecules exiting a GC column, but to date, GC-ESI has only been attempted by one group [65,66]. The results of Cha et al [65] showed that GC-ESI could achieve linearity, repeatability, robustness and detection limits comparable to standard GC-MS and LC-MS methods.…”