New Practice for Measurement of Volatile Organic Compounds Using H3O+ Ionization Proton-Transfer Reaction Mass Spectrometry (PTR-MS) for Indoor Environments
1. Scope
This standard practice outlines accepted procedures for measurement of volatile organic compounds (VOCs) using hydronium ion (H3O+) ionization proton-transfer reaction mass spectrometry (PTR-MS) under environmental conditions that are typical of those found in indoor environments, such as offices, residential buildings, and test chambers. Procedures to prepare and initialize an instrument for measurement, construct a sampling line and characterize performance, and convert instrument signal into indoor air concentrations are outlined. These procedures can be used to develop standard operating procedures for specific PTR-MS applications. This standard scope is limited to PTR-MS and is not inclusive of other reagent ions that can be used in real-time chemical ionization mass spectrometers. PTR-MS is used in this standard to describe a chemical ionization mass spectrometer that satisfies all the following criteria: capable of ionizing analytes with H3O+ as the primary reagent ion, real-time (i.e., at least 1 second) data acquisition, and is field-deployable. From this point on all instances of PTR-MS refer to the instrument and “proton-transfer reaction mass spectrometry” will be used when referring to the technique. Because the logistics and data quality objectives of each application using a PTR-MS will be unique, standardized procedures for measuring the concentrations of specific gases are not explicitly set forth in this practice. Instead, general procedures that are applicable to all PTR-MS instruments and most applications are described. Users should consult manufacturers for instrument-specific guidance and/or refer to scientific literature when considering applications not covered by this standard. This practice describes procedures appropriate for both short (e.g., minutes to hours) and long-term (e.g., days to weeks) sampling of indoor air.
Keywords
Proton-transfer reaction mass spectrometry; volatile organic compounds; real-time environmental monitoring; indoor air quality; environmental chambers; residential buildings
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.
