THESIS
2023
1 online resource (xiv, 79 pages) : illustrations (chiefly color)
Abstract
Organosulfates (OSs) are prominent components of secondary organic aerosols (SOA) and
have far-reaching implications for the environment. Among the various OS species, C
2-3
organosulfates (C
2-3OSs) have emerged as a crucial small-size subset with high reactivity that
contribute significantly to not only the overall abundance of OSs but also the new SOA
formation. Considering their important role as oxidation products derived from isoprene,
precise quantification data of C
2-3OSs allows for refined modeling of isoprene chemistry,
enabling a more accurate perception of its broader implications in atmospheric processes.
Despite the importance of airborne C
2-3OSs, few unambiguous measurements of these
compounds have been conducted, resulting in a critical data gap that needs to be addressed...[
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Organosulfates (OSs) are prominent components of secondary organic aerosols (SOA) and
have far-reaching implications for the environment. Among the various OS species, C
2-3
organosulfates (C
2-3OSs) have emerged as a crucial small-size subset with high reactivity that
contribute significantly to not only the overall abundance of OSs but also the new SOA
formation. Considering their important role as oxidation products derived from isoprene,
precise quantification data of C
2-3OSs allows for refined modeling of isoprene chemistry,
enabling a more accurate perception of its broader implications in atmospheric processes.
Despite the importance of airborne C
2-3OSs, few unambiguous measurements of these
compounds have been conducted, resulting in a critical data gap that needs to be addressed for
a comprehensive understanding of the relevant atmospheric chemistry. Existing data are often
obtained through offline liquid chromatography/mass spectrometry (LC/MS) methods that vary
in instrument configurations among different laboratories, particularly in the separation
techniques employed. This variability can lead to uncertainties when comparing results.
In this work, we evaluated the efficacy of two previously adopted LC methods – reverse-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) – coupled with ESI(-)-Orbitrap MS, in characterizing and quantifying PM
2.5-bound C
2-3OSs. Our results demonstrated that HILIC outperformed RPLC in retentive capacities and peak
resolving abilities, generating more reliable results closer to the true concentrations. In contrast,
RPLC failed to provide satisfactory outcomes, neither qualitatively nor quantitatively, due to
its poor retention of small polar analytes. The results from RPLC were significantly
underestimated, which was attributed to the prevalent matrix effect (ME) occurring in the gradient-front and the lack of adequate internal standards (ISs) for compensation. The presence
of abundant bisulfate ion eluting in proximity to the analytes was speculated as the dominant
endogenous suppressor attenuating the signal. Surprisingly, our supplementary experiment with
triple-quadrupole Qtrap MS showed that multiple reaction monitoring (MRM) mode produced
even more negatively biased results than the high-resolution Orbitrap system, indicating its
higher susceptibility to ME. False-positive signals resulting from insufficient mass resolution
were also identified.
Overall, this work serves as a case study highlighting the need for atmospheric chemistry
analysts to take note of the potential challenges and consider adopting appropriate analytical
methods to ensure accurate and reliable results in their research.
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