Speciating volatile organic compounds in indoor air: using in-situ GC to interpret real-time PTR-MS signals

Published

December 18, 2024

Author(s)

Jenna Ditto, Han Huynh, Jie Yu, Michael Link, Dustin Poppendieck, Megan Claflin, Marina Vance, Delphine Farmer, Arthur Chan, Jonathan Abbatt

Abstract

Proton transfer reaction mass spectrometry (PTR-MS) is often employed to characterize gas-phase compounds in both indoor and outdoor environments. PTR-MS measurements are usually made without upstream chromatographic separation, so it can be challenging to differentiate between an ion of interest, its isomers, and fragmentation products from other species all detected at the same mass-to-charge ratio. These isomeric and fragmentation interferences can confound the determination of accurate compound mixing ratios, the assignment of accurate chemical properties, and corresponding analyses of chemical fate. In this study, we deployed a gas chromatograph upstream of a PTR-MS to investigate interferences caused by isomers and fragmentation products for select indoor air-relevant chemicals. Measurements were made in a test house across a variety of indoor chemical sources, oxidants, and environmental conditions during the Chemical Assessment of Surfaces and Air (CASA) study. Observed interferences at each extracted ion chromatogram ranged from 0 % (C2H6OH+, C8H24O4Si4H+, and C10H30O5Si5H+) to 98 % (at C5H9+). For many ions, interferences varied between indoor conditions, and there were also differences between interferences across indoor versus outdoor measurements. The relative contribution of sets of key structural isomers (e.g., C6-C8 carbonyls, xylenes, trimethylbenzenes, and monoterpenes) remained consistent throughout the measurement period despite changing indoor conditions. These relatively stable isomer distributions yielded stable chemical property assignments for these isomer sets. Taken together, these observations can inform future interpretations of PTR-MS signals measured without upstream chromatography in different indoor conditions.

Citation

Environmental Science: Processes and Impacts

Pub Type

Journals

Download Paper

https://doi.org/10.1039/D4EM00602J

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Keywords

indoor air quality, volatile organic compounds, gas chromatography, chemical ionization mass spectrometry

Citation

Ditto, J. , Huynh, H. , Yu, J. , Link, M. , Poppendieck, D. , Claflin, M. , Vance, M. , Farmer, D. , Chan, A. and Abbatt, J. (2024), Speciating volatile organic compounds in indoor air: using in-situ GC to interpret real-time PTR-MS signals, Environmental Science: Processes and Impacts, [online], https://doi.org/10.1039/D4EM00602J, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958645 (Accessed December 2, 2025)