Proton transfer reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS) are well-established, field-deployable chemical ionization technologies known for their portability.
These techniques enable the high-resolution detection of numerous gases, capturing multiple measurements per second at extremely low concentrations—down to pmol mol⁻¹, equivalent to a single drop of water in an Olympic-sized swimming pool.
Both methods employ various reagent ions to ionize target compounds, facilitating their identification. One of the most commonly used reagent ions is the hydronium ion (H₃O⁺), which ionizes all substances with proton affinities greater than that of water. This characteristic minimizes interference from major atmospheric components such as argon, carbon dioxide, nitrogen, and oxygen, eliminating the need for sample pretreatment.
PTR-MS and SIFT-MS detect compounds as protonated molecular ions, preserving their integrity due to the minimal excess energy involved in the proton transfer reaction. This feature allows for the identification of compounds in complex mixtures without requiring conventional chromatographic separation.
These techniques are particularly valuable in time-sensitive applications, offering real-time measurements across various industries and research fields since their introduction in the mid-1990s. Their applications include air quality monitoring, breath analysis, biomedical research, illegal substance detection, environmental studies, food and flavor science, and safety and security.
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