Detection of Polycyclic Aromatic Hydrocarbons in High Organic Carbon Ultrafine Particle Extracts by Electrospray Ionization Ultrahigh-Resolution Mass Spectrometry

Abstract

The detection of polycyclic aromatic hydrocarbons (PAHs) by electrospray ionization (ESI) without additional reagents or targeted setup changes to the ionization source was observed in ultrafine particle (UFP) extracts, with high organic carbon (OC) concentrations, generated by a combustion aerosol standard (CAST) soot generator. Particulate matter (PM) was collected on filters, extracted with methanol, and analyzed by ESI Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Next to oxygen-containing species, pure hydrocarbons were found to be one of the most abundant compound classes, detected as [M + Na]+ or [M + H]+ in ESI+ and mostly as [M – H]− in ESI–. The assigned hydrocarbon elemental compositions are identified as PAHs due to their high aromaticity index (AI > 0.67) and were additionally confirmed by MS/MS experiments as well as laser desorption ionization (LDI). Thus, despite the relatively low polarity, PAHs have to be considered in the molecular attribution of these model aerosols and/or fresh emissions with low salt content investigated by ESI.

Chemometric Analysis Combined with GC × GC-FID and ESI HR-MS to Evaluate Ultralow-Sulfur Diesel Stability

“…The authors concluded that the low polar content characteristic of the matrix studied is the main factor corroborating the detection of hydrocarbons by ESI. 71 In the present study, the distribution of DBE for the HC class, illustrated in Figure S12 for the negative- and positive-ion mode, showed the detection of aromatic species with DBE greater than 4, corroborating the results reported by Schneider et al…”

“…The ionization of hydrocarbons by ESI (+) is a more complex process and involves factors related to the composition of the matrix and, above all, the ionization process characteristic of ESI. , In a study reported by Schneider et al, the ionization of polyaromatic hydrocarbons led to the formation of ions of the [M + H] + type. The authors concluded that the low polar content characteristic of the matrix studied is the main factor corroborating the detection of hydrocarbons by ESI . In the present study, the distribution of DBE for the HC class, illustrated in Figure S12 for the negative- and positive-ion mode, showed the detection of aromatic species with DBE greater than 4, corroborating the results reported by Schneider et al…”

“…Hydrocarbons were detected by ESI in both ionization modes. The detection of this class of compounds is also related to the low content of polar constituents in ULSD samples, which contributes to reduce the ion suppression effect of polar compounds on hydrocarbons, enabling their ionization and subsequent detection of that class . In ESI (−) analysis, the HC class refers to the presence of hydrocarbons with a Csp 3 , which promotes deprotonation due to the formation of an aromatic carbanion that is stabilized by resonance …”

“…The detection of this class of compounds is also related to the low content of polar constituents in ULSD samples, which contributes to reduce the ion suppression effect of polar compounds on hydrocarbons, enabling their ionization and subsequent detection of that class. 71 In ESI (−) analysis, the HC class refers to the presence of hydrocarbons with a Csp 3 , which promotes deprotonation due to the formation of an aromatic carbanion that is stabilized by resonance. 72 The ionization of hydrocarbons by ESI (+) is a more complex process and involves factors related to the composition of the matrix and, above all, the ionization process characteristic of ESI.…”