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New Practice for Measurement of Volatile Organic Compounds Using H3O+ Proton Transfer Reaction Mass Spectrometry (PTR-MS) in Indoor Environments
1. Scope
Overview of Instrumentation and Ion Chemistry
- Mass spectrometry, H3O+ ion chemistry (with noting of impurity NO+ and O2+ reagent ion chemistries), and VOCs well-suited for PTR-MS measurement
- Types of instruments that use H3O+ chemical ionization, highlighting notable differences
Sampling Methods
- Materials, flowrates, supplemental pumps and temperature control
- Limitations
Calibration and Quantification
- Approaches
- Recommended VOC calibration mixtures for indoor air quality analyses
- Methods Quantifying ions from parameterizations of calibrated VOC sensitivities versus proton-transfer rate coefficients
- Determination of relative transmission efficiency as a function of mass-to-charge ratio
- Determination of proton-transfer rate coefficients
- Correcting measured sensitivities for fragmentation and duty cycle
Data processing steps, calculations, and assessing data quality
- Assessing uncertainties from isomers and product ion interferences in measured VOC concentrations
- Methods of data post-processing: reagent ion normalization, humidity corrections, and duty cycle corrections
- Differences in VOC quantification as a function of mass resolution (e.g., use of quadrupole versus time-of-flight mass analyzers)
Keywords
proton-transfer mass spectrometry; volatile organic compounds; chemical ionization mass spectrometry
Rationale
Recent technological advances in air monitoring instrumentation (e.g. proton transfer reaction mass spectrometry, PTR-MS) have enabled the measurement of chemicals at orders of magnitude higher time and lower concentration resolutions compared to older instrumentation. However, quantification using this new equipment is challenged in part because of a paucity of standards that define operational best practices and data quality control procedures. Increasingly, standard test methods are recommending PTR-MS instruments for measurement of volatile organic compounds in indoor environments (e.g., ASHRAE 145.2 and 145.4, ASTM D6670, ISO 16000-3). Measurement and quantification of volatile organic compounds indoors is currently performed in a variety of applications including product emissions testing, chamber and in-duct testing and safety verification of air cleaning technologies, and wildfire smoke damage testing—to name a few. Additionally, the private consumer market demands for disaster response and smoke damage measurements are growing.
