Ethylene: absolute real-time high-sensitivity detection with PTR/SRI-MS: the example of fruits, leaves and bacteria

Ethylene is a gaseous hormone playing a fundamental role in many systems and its detection and quantification is often crucial for several research fields. In the present work we investigated the possibility to employ Proton Transfer Reaction-Mass Spectrometry (PTR-MS) instruments modified by a Selective Reagent Ionization (SRI) upgrade to detect ethylene in real time with high sensitivity. Compared to commercial laser-based instruments the performance of SRI-MS is similar in terms of detection limits and superior as far as response time and dynamic range are concerned. We showed that, with SRI coupled to a time-of-flight (ToF) mass analyzer, absolute ethylene determination is possible. We experimentally determined the reaction rate coefficients for ethylene reactions with H3O+, O2+ and NO+ as primary ions in the SRI-MS drift tube and proved that in the case of O2+ such reaction proceeds at collision rate, while in the case of H3O+ and NO+ the reaction is less efficient. Reaction product yields and their eventual dependence on the buffer gas were investigated. New product ions that were not previously reported were found. We concluded that among the explored instrumental set-ups, the preferable one for ethylene detection with SRI-ToF-MS is O2+ mode, considering the C2H4+ ion signal at m/z 28.0307. We finally showed that SRI-MS is a powerful tool for ethylene investigations in biological samples