Proton transfer reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS) are well-established, portable chemical ionization technologies designed for field deployment.
These techniques provide high-resolution gas detection, capturing multiple measurements per second at ultra-low concentrations—down to pmol mol⁻¹, comparable to a single drop of water in an Olympic-sized swimming pool.
Both methods utilize different reagent ions to ionize target compounds, aiding their identification. A key reagent ion, hydronium (H₃O⁺), selectively ionizes compounds with proton affinities higher than water. This selectivity reduces interference from major atmospheric gases such as nitrogen, oxygen, carbon dioxide, and argon, eliminating the need for sample pretreatment.
By detecting compounds as protonated molecular ions, PTR-MS and SIFT-MS ensure minimal fragmentation due to the low excess energy involved in the proton transfer reaction. This capability allows for the analysis of complex mixtures without requiring traditional chromatographic separation.
Since their introduction in the mid-1990s, these techniques have become indispensable in real-time monitoring across various industries and research fields. Their applications range from air quality monitoring and breath analysis to biomedical research, illicit substance detection, environmental studies, food and flavor science, and security screening.
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