Reactive carbon fiber ionization-mass spectrometry for characterization of unsaturated hydrocarbons from plant aroma

Carbon fiber ionization (CFI)-mass spectrometry (MS) is an ambient technique that can be used to detect samples in gas, liquid, and solid forms simply by using a piece of carbon fiber as the ionization emitter. Reactive MS can be performed to selectively detect target analytes by conducting fast reactions during ionization. Most ambient ionization MS techniques used to monitor chemical reactions are limited to liquid-phase reactions. Herein, we develop reactive CFI-MS to be a suitable tool for monitoring of reaction products derived from volatile unsaturated hydrocarbons in the gas phase. Hydroamination is a fast reaction that can form a carbon-nitrogen bond through the addition of an amine to unsaturated hydrocarbons. In this study, reactive CFI-MS was used to selectively characterize aroma molecules, which are unsaturated hydrocarbons derived from plants, through hydroamination. A piece of carbon fiber was placed close (~ 1 mm) to the inlet of the mass spectrometer and deposited with dried methylamine. The sample in either liquid or solid form was placed underneath the carbon fiber. The volatiles derived from the sample reacted with amine on the carbon fiber were simultaneously determined once the mass spectrometer was switched on. For proof of concept, ethylene glycol dimethacrylate, which has double bonds and is highly volatile, was initially selected as the model sample to demonstrate the feasibility of using reactive CFI-MS to detect its hydroamination derivative. Banana, garlic, and ginger, which possess aroma molecules with unsaturated hydrocarbons, were selected as real-world samples. Graphical abstract.