Ion-molecule reactions (IMR) are at the very core of trace gas analyses in modern chemical ionization (CI) mass spectrometer instruments, which are increasingly being used in diverse areas of research and industry. The focus of this Perspective is on the ion chemistry that underpins gas-phase analytical CI methods. Special attention is given to the soft chemical ionization method known as selected ion flow tube-mass spectrometry (SIFT-MS). The processes involved in the ion chemistry of the reagent cations, H3O+, NO+, and O2+•, and the anions, O-•, O2-•, OH-, and NO2-, are discussed in some detail. Stressed throughout is that an understanding of these processes is mandatory to obtain reliable analyses of humid gaseous media such as ambient air and exhaled breath. It is indicated that further research is needed to understand the consequences of replacing helium in some situations by the more readily available nitrogen as the carrier gas in SIFT-MS.

Department of Chemistry University of Canterbury Private Bag 4800 Christchurch 8140 New Zealand

J Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences Dolejškova 3 18223 Prague 8 Czech Republic

References provided by Crossref.org

A SIFT Study of Reactions of Positive and Negative Ions With Polyfluoroalkyl (PFAS) Molecules in Dry and Humid Nitrogen at 393 K

Recent developments and applications of selected ion flow tube mass spectrometry (SIFT-MS)

Robust Automated SIFT-MS Quantitation of Volatile Compounds in Air Using a Multicomponent Gas Standard

How to Use Ion-Molecule Reaction Data Previously Obtained in Helium at 300 K in the New Generation of Selected Ion Flow Tube Mass Spectrometry Instruments Operating in Nitrogen at 393 K

Selected ion flow tube mass spectrometry for targeted analysis of volatile organic compounds in human breath