Proton-extraction-reaction mass spectrometry (PER-MS) for monitoring organic and inorganic compounds

• A novel PER-MS with reagent ions OH− was developed for trace analysis.
• PER-MS can detect both organic and inorganic compounds.
• Hydroxyl anions OH− were extracted from the ion source of a discharge in water vapor.
• PER-MS can be used to determine the molecular weight of VOCs unambiguously combined with conventional PTR-MS.

In the conventional proton-transfer-reaction mass spectrometry (PTR-MS), reagent ions of H3O+ were prepared with a discharge source of water vapor. For the identification of VOCs that can not be detected in conventional PTR-MS, other ions, e.g., NO+ and O2+, were exploited. However, these ions must be prepared with other reagent gases. In this work, hydroxyl anions OH− were prepared with only water vapor in the discharge source of conventional PTR-MS to develop a novel proton-extraction-reaction mass spectrometry (PER-MS). By using reverse electric fields for ion extraction and ion drift, the reagent ions OH− in the discharge source were introduced into the drift tube in PER-MS, and interacted with volatile organic compounds (VOCs) via proton extraction reaction. The relative abundances of cluster ions (H2O)nOH− (n = 0–4) at different reduced fields in the drift tube show the similar characteristic of cluster ions to that in conventional PTR-MS. Some common VOCs were introduced into PER-MS, and the deprotonated VOCs were detected. Moreover, carbon dioxide was also detected in PER-MS via the association reaction. The results show the ability of PER-MS to detect both organic and inorganic compounds. The newly developed PER-MS combined with conventional PTR-MS can supply more powerful analytical ability in many application fields.

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