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Webinar Series: Sampling with Vocus CI-TOF Mass Spectrometers -Part 1

vocus inlet design and sampling


Inlet design is a critical part of any experiment that samples and characterizes air. In this webinar series, we present important concepts for inlet design, and suggest how different experiments may be connected to Vocus chemical ionization mass spectrometers.

If you have questions about the webinar, have a suggestion for a topic to include in future versions, or would like to add to the webinar bibliography, please feel free to contact us at

Key Discussion Points – Part 1

  • Understanding inlet effects on time response and sensitivity
  • Practical considerations for building an inlet
  • Common problems with sampling and how to avoid them
  • Inlet passivation and depassivation
  • Correcting data for inlet effects

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Webinar Bibliography

Examples of inlet effects:

Rivera-Rios, J. C., Nguyen, T. B., Crounse, J. D., Jud, W., St. Clair, J. M., Mikoviny, T., Gilman, J. B., Lerner, B. M., Kaiser, J. B., de Gouw, J. A., Wisthaler, A., Hansel, A., Wennberg, P. O., Seinfeld, J. H., and Keutsch, F. N.:Conversion of hydroperoxides to carbonyls in field and laboratory instrumentation: Observational bias in diagnosing pristine versus anthropogenically controlled atmospheric chemistry, Geophys. Res. Lett., 41, 8645–8651, doi:10.1002/ 2014GL061919, 2014.

Bernhammer, A.-K., Breitenlechner, M., Keutsch, F. N., and Hansel, A.: Technical note: Conversion of isoprene hydroxy hydroperoxides (ISOPOOHs) on metal environmental simulation chamber walls, Atmos. Chem. Phys., 17, 4053–4062,, 2017.

Kleffman, J., Becker, K. H., Wiesen, P.: Heterogeneous NO2 conversion processes on acid surfaces: possible atmospheric implications. Atmos. Environ., 32 (16), 2721-2729, 1998.

Analyte/inlet interactions:

Liu, X., Deming, B., Pagonis, D., Day, D. A., Palm, B. B., Talukdar, R., Roberts, J. M., Veres, P. R., Krechmer, J. E., Thornton, J. A., de Gouw, J. A., Ziemann, P. J., and Jimenez, J. L.: Effects of gas–wall interactions on measurements of semivolatile compounds and small polar molecules, Atmos. Meas. Tech., 12, 3137–3149,, 2019.

Pagonis, D., Krechmer, J. E., de Gouw, J., Jimenez, J. L., and Ziemann, P. J.: Effects of gas–wall partitioning in Teflon tubing and instrumentation on time-resolved measurements of gas-phase organic compounds, Atmos. Meas. Tech., 10, 4687–4696,, 2017.

Deming, B. L., Pagonis, D., Liu, X., Day, D. A., Talukdar, R., Krechmer, J. E., de Gouw, J. A., Jimenez, J. L., and Ziemann, P. J.: Measurements of delays of gas-phase compounds in a wide variety of tubing materials due to gas–wall interactions, Atmos. Meas. Tech., 12, 3453–3461,, 2019.

Palm, B. B., Liu, X., Jimenez, J. L., and Thornton, J. A.: Performance of a new coaxial ion–molecule reaction region for low-pressure chemical ionization mass spectrometry with reduced instrument wall interactions, Atmos. Meas. Tech., 12, 5829–5844,, 2019.

Huang, Y., Zhao, R., Charan, Sp. M., Kenseth, C. M., Zhang, X., Seinfeld, J. H. Unified theory of vapor-wall mass transport in teflon-walled environmental chambers. Environ. Sci. Technol., 52(4), 2134-2142,, 2018.

Neuman, J. A., Huey, L. G., Ryerson, T. B., Fahey, D. W. Study of inlet materials for sampling atmospheric nitric acid. Environ. Sci. Technol. 1999, 33, 7, 1133-1136.

Inlet passivation:

Roscioli, J. R., Zahniser, M.S., Nelson, D.D., Herndon, S.C., Kolb, C.E.: New Approaches to Measuring Sticky Molecules: Improvement of Instrumental Response Times Using Active Passivation. J. Phys. Chem. A., 129, 9, 1347-1357,, 2016.

Pollack, I. B., Lindaas, J., Rosciolli, J. R., Agnese, M., Permar, W., Hu, L., Fischer, E. V.: Evaluation of ambient ammonia measurements from a research aircraft using a closed-path QC-TILDAS operated with active continuous passivation. Atmos. Meas. Tech., 12, 3717-3742,, 2019.

Webinar Presenter

Dr. Abigail Koss is an Application Scientist at TOFWERK USA in Boulder, CO. She is an international PTR-MS expert, with extensive experience in environmental fieldwork for atmospheric chemistry. Her research focal points include chemical ionization instrument development and interpretation techniques for large mass spectrometry datasets.