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Characterization of aerosol nitroaromatic compounds: Validation of an experimental method
Citation:
Jaoui, M., M. Lewandowski, J. Offenberg, M. Colon, K. Docherty, AND Tad Kleindienst. Characterization of aerosol nitroaromatic compounds: Validation of an experimental method. Journal of Mass Spectrometry. John Wiley & Sons, Ltd., Indianapolis, IN, 53(8):680-692, (2018). https://doi.org/10.1002/jms.4199
Impact/Purpose:
Ambient aerosols are complex mixtures of water, carbonaceous compounds, inorganic salts, metals, and mineral dust.1 These particles can have direct environmental impacts by scattering light or absorbing solar radiation, leading to visibility degradation2,3 and altering the amount of solar radiation reaching the surface of the earth.4 Ultrafine particles can also indirectly affect cloud properties and the hydrological cycle by acting as cloud condensation nuclei.5,6 In addition, it is fairly well established that extended exposures to fine particulate matter (PM2.5) can lead to adverse health effects.7,8 It is expected that understanding the molecular composition will be required to help explain the toxic properties associated with PM2.5.
Description:
The analytical capabilities associated with the use of silylation reactions have been extended to a new class of organic molecules, nitroaromatic compounds (NACs). These compounds are a possible contributor to urban particulate matter of secondary origin which would make them important analytes due to their (1) detrimental health effects, (2) potential to affect aerosol optical properties, and (3) and usefulness for identifying PM2.5 from biomass burning. The technique is based on derivatization of the parent NACs by using N,O‐bis‐(trimethylsilyl)‐trifluoro acetamide, one of the most prevalent derivatization reagent for analyzing hydroxylated molecules, followed by gas chromatography‐mass spectrometry using electron ionization (EI) and methane chemical ionization (CI). This method is evaluated for 32 NACs including nitrophenols, methyl‐/methoxy‐nitrophenols, nitrobenzoic acids, and nitrobenzyl alcohols. Electron ionization spectra were characterized by a high abundance of ions corresponding to [M+] or [M+ − 15]. Chemical ionization spectra exhibited high abundance for [M+ + 1], [M+ − 15], and [M+ + 29] ions. Both EI and CI spectra exhibit ions specific to nitro group(s) for [M+ − 31], [M+ − 45], and [M+ − 60]. The strong abundance observed for [M+] (EI), [M+ − 15] (EI/CI), or [M+ + 1] (CI) ions is consistent with the high charge stabilizing ability associated with aromatic compounds. The combination of EI and CI ionization offers strong capabilities for detection and identification of NACs. Spectra associated with NACs, containing hydrogen, carbon, oxygen, and nitrogen atoms only, as silylated derivatives show fragment/adduct ions at either (a) odd or (b) even masses that indicate either (a) odd or (b) even number of nitro groups, respectively. Mass spectra associated with silylated NACs exhibited 3 distinct regions where characteristic fragmentation with a specific pattern associated with (1) ─OH and/or ─COOH groups, (2) ─NO2 group(s), and (3) benzene ring(s). These findings were confirmed with applications to chamber aerosol and ambient PM2.5.
URLs/Downloads:
DOI: Characterization of aerosol nitroaromatic compounds: Validation of an experimental method
https://doi.org/10.1002/jms.4199