Introducing the extended volatility range proton-transfer-reaction mass spectrometer (EVR PTR-MS)

Piel, Felix; Müller, Markus; Winkler, Klaus; Skytte af Sätra, Jenny; Wisthaler, Armin

Proton-transfer-reaction mass spectrometry (PTR-MS) is widely used in atmospheric sciences for measuring volatile organic compounds in real time. In the most widely used type of PTR-MS instruments, air is directly introduced into a chemical ionization reactor via an inlet capillary system. The reactor has a volumetric exchange time of inline-formula∼0.1 s, enabling PTR-MS analyzers to measure at a frequency of 10 Hz. The time response does, however, deteriorate if low-volatility analytes interact with surfaces in the inlet or in the instrument. Herein, we present the extended volatility range (EVR) PTR-MS instrument which mitigates this issue. In the EVR configuration, inlet capillaries are made of passivated stainless steel, and all wetted metal parts in the chemical ionization reactor are surface-passivated with a functionalized hydrogenated amorphous silicon coating. Heating the entire setup (up to 120 inline-formulaC) further improves the time-response performance.

We carried out time-response performance tests on a set of 29 analytes having saturation mass concentrations inline-formulaC0 in the range between inline-formula10−3 and inline-formula105inline-formulaµg m−3. The inline-formula M7inlinescrollmathml normal 1 / e 21pt14ptsvg-formulamathimg82e0823fe03ff0dee1c3117688ee2eff amt-14-1355-2021-ie00001.svg21pt14ptamt-14-1355-2021-ie00001.png -signal decay times after instant removal of the analyte from the sampling flow were between 0.2 and 90 s for gaseous analytes. We also tested the EVR PTR-MS instrument in combination with the chemical analysis of aerosols online (CHARON) particle inlet, and inline-formula M8inlinescrollmathml normal 1 / e 21pt14ptsvg-formulamathimg416b5cf6c9c03be8e7b25ad586ee718a amt-14-1355-2021-ie00002.svg21pt14ptamt-14-1355-2021-ie00002.png -signal decay times were in the range between 5 and 35 s for particulate analytes. We show on a set of example compounds that the time-response performance of the EVR PTR-MS instrument is comparable to that of the fastest flow tube chemical ionization mass spectrometers that are currently in use. The fast time response can be used for rapid (inline-formula∼1 min equilibration time) switching between gas and particle measurements. The CHARON EVR PTR-MS instrument can thus be used for real-time monitoring of both gaseous and particulate organics in the atmosphere. Finally, we show that the CHARON EVR PTR-MS instrument also rapidly detects highly oxygenated species (with up to eight oxygen atoms) in particles formed by limonene ozonolysis.

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Piel, Felix / Müller, Markus / Winkler, Klaus / et al: Introducing the extended volatility range proton-transfer-reaction mass spectrometer (EVR PTR-MS). 2021. Copernicus Publications.

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