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 quan-tification is often crucial for several research fields. In the present work we investigated the possibilityto employ Proton Transfer Reaction-Mass Spectrometry (PTR-MS) instruments modified by a SelectiveReagent Ionization (SRI) upgrade to detect ethylene in real time with high sensitivity. Compared to com-mercial laser-based instruments the performance of SRI-MS is similar in terms of detection limits andsuperior as far as response time and dynamic range are concerned. We showed that, with SRI coupledto a time-of-flight (ToF) mass analyzer, absolute ethylene determination is possible. We experimentallydetermined the reaction rate coefficients for ethylene reactions with H3O+, O2+and NO+as primary ionsin the SRI-MS drift tube and proved that in the case of O2+such reaction proceeds at collision rate, whilein the case of H3O+and NO+the reaction is less efficient. Reaction product yields and their eventualdependence on the buffer gas were investigated. New product ions that were not previously reportedwere found. We concluded that among the explored instrumental set-ups, the preferable one for ethyl-ene detection with SRI-ToF-MS is O2+mode, considering the C2H4+ion signal at m/z 28.0307. We finallyshowed that SRI-MS is a powerful tool for ethylene investigations in biological samples.