Session: Advances in Mass Spectrometry:

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds containing multiple aromatic rings formed during incomplete combustion. They are known mutagens and carcinogens. PAHs in the particulate matter (PM) are increasing concerns because some polar PAHs found in PM of wildfire smoke may be more harmful than the non-polar PAHs. Levels of PAHs in the PM are critical to evaluate their health effects. However, quantification of PAHs using the conventional chromatographic approaches is often time consuming and laborious. Herein, we describe a novel method for quantifying non-polar and polar PAHs in the PM of smoke by direct analysis in real-time mass spectrometry (DART-MS).
Air was drawn through the cassettes with a clean quartz filter using SKC Airchek sampling pump at 3 L/min. A reference method based on gas chromatography-mass spectrometry (GC-MS) was developed by following EPA standard method (Compendium Method TO-13A). The filter was extracted by methanol-dichloromethane mix. The sample extract was evaporated using a nitrogen evaporator to dryness, reconstituted using 2 mL of methylene chloride, and then filtered using a nylon syringe filter before the GC-MS analysis. Precut filter samples were placed on a thermal desorption device, and the desorbed PAHs were detected directly by DART-MS. The certified PM samples and field PM samples were analyzed by both GC-MS and DART-MS methods, and the results were compared.
Significant levels of multiple non-polar PAHs and polar PAHs were detected in the PM of air samples collected in California during the wildfire season of fall 2020. The proposed DART-MS method allows the simultaneous quantification of non-polar PAHs, hydroxyl PAHs, nitro-PAHs, and oxygenated PAHs with minimum sample preparation. It can potentially serve as an alternative approach for wildfire smoke composition analysis, with higher throughput than the chromatographic methods.

Steven Pham

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