Fragmentation Analysis of α-Pinene Oxidation Products Using High-Resolution Collision-Induced Dissociation Mass Spectrometry for Application to Functional Group Prediction in Monoterpene Oxidation Products without Chromatography

Monoterpenes are oxidized in the atmosphere, forming highly oxygenated organic molecules as key precursors for secondary organic aerosols. The resulting oxidation products are well-known to have a large number of structural isomers with multiple oxygen-containing functional groups. However, the precise structures and functionalities of most isomers remain unidentified. In this study, we developed an online analytical method for indicating the presence of oxygen-containing functional groups (carboxyl, hydroxyl, hydroperoxyl, and carbonyl groups) included in gas-phase monoterpene oxidation products. This approach utilizes high-resolution collision-induced dissociation mass spectrometry (HR-CID-MS) in combination with an ambient ionization technique based on atmospheric pressure chemical ionization. We established a relationship between oxygen-containing functional groups and neutral loss observed in the CID spectra of (de)protonated α-pinene oxidation products. The method was applied to α-pinene ozonolysis products, successfully predicting functional groups in known compounds and enabling the characterization of previously unreported ozonolysis products.