PTR-MS: Moving mass spectrometry into the field.

Advanced Technology: Proton Transfer Reaction Mass Spectrometer (PTR-MS)

Mass spectrometry is a critical component in many analytical techniques used to identify and quantify organic compounds in a variety of sample matrices, from both environmental and industrial sources. The foundational principle is that individual chemical compounds have a known molecular weight that can be used to identify and quantify them.

The physics behind the analytical methods are complex, but simply put, a charge is added to each molecule (ionizing) to allow for mass separation, detection, and quantification using a mass spectrometer. This analysis commonly results in the fragmentation of larger molecules into smaller ones, complicating interpretation because the pattern of the fragmented masses needs to be identified and used to identify and quantify the original larger molecules.

Due to the delicate nature of these analytical operations, most mass spectrometers can only operate within the stable confines of a laboratory. The advent of PTR-MS technology addressed several limitations of the benchtop units used in the laboratory. PTR-MS is a “soft” ionization mass spectrometer. Charge is added to each molecule using water, oxygen, or nitrogen oxide molecules which suppress the fragmentation of the compounds, allowing for a more robust analysis of the mass spectrum.

PTR-MS is particularly adept at the identification and measurement of volatile organic compounds (VOCs) in air. It can provide real-time, continuous measurement of multiple volatile organic compounds (VOCs) at ultra-trace levels, i.e., in the parts per trillion (ppt) and low parts per billion (ppb) range. A truck-mounted solution also gives the instrument mobility for environmental monitoring and sourcing investigations.

The PTR-MS has been used in many peer-reviewed studies for the detection of VOCs. Studies include ambient measurements for the investigation of the air quality of urban and suburban areas.^1,2 The information that the PTR-MS provides can be used in air quality source apportionment studies to gain insight into the sources of different air toxins such as toluene, xylene, and benzene; biogenic compounds emitted by vegetation, such as isoprene, monoterpenes, and sesquiterpenes; and other compounds such as acetaldehyde, formaldehyde, and acetone.^3,4

Other studies have used the PTR-MS for the detection of emissions from different sources, such as biomass burning^5,6, cooking activities⁷, and diesel exhaust⁸. Other applications include the testing of emissions from materials, investigation of indoor air quality, and vapor intrusion studies^9-12. Most recently the device was used for the breath analysis and identification of biomarkers of Covid-19 patients¹³. The ability of real-time detection of VOCs makes the PTR-MS the ideal instrument for these applications.

Application: Headspace sampling

Due to its high sensitivity and low time resolution, the PTR-MS is the perfect tool for headspace sampling. RJ Lee Group has implemented the PTR-MS in several headspace projects for the detection of emissions from carbon black, canned food products, as well as products such as gloves and face masks. In a previous study, RJ Lee Group investigated the compounds emitted by a medical device.

The device was placed in a testing Tedlar bag, which was filled with clean air. The PTRMS was used to monitor the VOC concentration inside the bag. After the device was turned on, the concentration of 6 compounds increased. After two hours of testing, compounds such as butadiene and hexynes had reached a plateau at a concentration lower than 5 ppb (Figure 1). The concentration of acetone, acetic acid, isoprene and butene continued increasing during the whole testing period.

Application: Mobile field measurements

The PTR-MS can also be used to study the air quality of an area. The combination of the PTRMS with RJ Lee Group’s mobile laboratory can allow for temporal and spatial resolution air quality measurements. Our scientists have conducted numerous fenceline monitoring and community air quality monitoring projects.

In one study we measured the ambient concentration of benzene in the greater area of Philadelphia. We were able to identify the higher emitters and investigate their impact on the neighboring communities. 

The concentration of benzene in the greater Philadelphia area. The altitude and the color of the series are proportional to the concentration of benzene.

PTR-MS technology offers an unparalleled combination of speed, sensitivity, and mobility, making it ideal for real-time air monitoring, environmental analysis, and quality control in diverse industries. By bringing advanced VOC analysis directly to the point of need, PTR-MS eliminates the limitations of traditional, lab-based methods—providing actionable insights instantly.

RJ Lee Group's mobile capabilities empower customers to make faster, data-driven decisions and maintain compliance without costly delays or sample degradation. For organizations looking to elevate their analysis capabilities, PTR-MS represents not just a tool, but a powerful advantage in a competitive landscape.

References: 

1. De Gouw, J. A., Welsh-Bon, D., Warneke, C., Kuster, W. C., Alexander, L., Baker, A. K., Beyersdorf, A. J., Blake, D. R., Canagaratna, M., Celada, A. T., et al.: Emission and chemistry of organic carbon in the gas and aerosol
phase at a sub-urban site near Mexico City in March 2006 during the MILAGRO study. Atmos. Chem. Phys.,9, 3425-3442, 2009.
2. Shah, R. U., Coggon, M. M., Gkatzelis, G. I., McDonald, B. C., Tasoglou, A., Heinz Huber, Jessica Gilman, J., Warneke, C., Robinson, A. L. Presto, A.: Observational evidence of the importance of secondary organic aerosol of
volatile chemical products, Environ. Sci. Technol.,54 (2), 714-725, 2020.
3. Kaltsonoudis, C., Kostenidou, E., Florou, K., Psichoudaki, M., Pandis, S. N.: Temporal variability and sources of VOCs in urban areas of the eastern Mediterranean, Atmos. Chem. Phys., 16, 14825–14842, 2016.
4. Crippa, M., Canonaco, F., Slowik, J. G., El Haddad, I., DeCarlo, P. F., Mohr, C., Heringa, M. F., Chirico, R., Marchand, N., Temime-Roussel, B., Abidi, E., Poulain, L., Wiedensohler, A., Baltensperger, U., and Prévôt, A. S. H.:
Primary and secondary organic aerosol origin by combined gas-particle phase source apportionment, Atmos. Chem. Phys., 13, 8411–8426, 2013.
5. Tasoglou, A., Saliba, G., Subramanian, R., Pandis, S. N.: Absorption of Chemically Aged Biomass Burning Carbonaceous Aerosol, J. Aerosol. Sci., 113, 141–52, 2017.
6. Gilman, J. B., Lerner, B. M., Kuster, W. C., Goldan, P. D., Warneke, C., Veres, P. R., Roberts, J. M., de Gouw, J. A., Burling, I. R., and Yokelson, R. J.: Biomass burning emissions and potential air quality impacts of volatile
organic compounds and other trace gases from fuels common in the US, Atmos. Chem. Phys., 15, 13915–13938, 2015.
7. Klein, F., Platt, S. M., Farren, N. J., Detournay, A., Bruns, E. A., Bozzetti, C., Daellenbach, K. R., Kilic, D., Kumar, N. K., Pieber, S. M., et al.: Characterization of gas-phase organics using proton transfer reaction time-of-flight
mass spectrometry: cooking emissions, Environ. Sci. Technol., 50, 1243-1250, 2016.
8. Inomata, S., Tanimoto, H., Fujitani, Y., Sekimoto, K., Sato, K., Fushimi, A., Yamada, H., Hori, S., Kumazawa, Y., Shimono, A., et al.: On-line measurements of gaseous nitro-organic compounds in diesel
vehicle exhaust by proton-transfer-reaction mass spectrometry, Atmos. Environ., 73, 195-203, 2013.
9. Sears, J.; Rogers, T.; McCoskey, J.; Lockrem, L.; Watts, H.; Pingel, L.; Conca, J. Proton Transfer Reaction Mass Spectrometry as a Real-Time Method for Continuous Soil Organic Vapor Detection. In Continuous Soil Gas
Measurements: Worst Case Risk Parameters; ASTM International: 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, 32-44, 2013.
10.Peinado, I., Marco, M., Franco, B., Scampicchio, M..: Hyphenation of Proton Transfer Reaction Mass Spectrometry with Thermal Analysis (TG/TR-MS) for Monitoring the Thermal Degradation of Retinyl Acetate, Rapid
Commun. Mass Spectrom. 32, 57-62, 2018.
11. Rosales, C. M. F., Jiang, J., Lahib, A., Bottorff, B. P., Reidy, E. K., Kumar, V., Tasoglou, A., Huber, H., Dusanter, S., Tomas, A., Boor, B. E., Stevens, P. S.: Chemistry and human exposure implications of secondary organic aerosol
production from indoor terpene ozonolysis, Sci. Adv., 8, 2022.
12.Wu, T., Tasoglou, A., Huber, H., Stevens, P. S., Boor, B. E.: Influence of Mechanical Ventilation Systems and Human Occupancy on Time-Resolved Source Rates of Volatile Skin Oil Ozonolysis Products in a LEED-Certified
Office Building, Environ. Sci. Technol. Lett., 24, 16477-16488, 2021.
13.Liangou, A., Tasoglou, A., Heinz J. H. J., Wistrom, C., Brody, K., Menon, P. G., Bebekoski, T., Menschel, K., Davidson-Fiedler, M., DeMarco, K., Salphale, H. Wistrom, J., Wistrom, S., Lee, R. J.: A novel method for the
identification of COVID-19 biomarkers in human breath using the PTR-ToF-MS, EclinicalMedicine, 42, 101207, 2021.