Absolute real-time non-destructive ethylene detection with SRI-MS and PTRMS: the example of fruits, leaves and bacteria

The goal of this work is to demonstrate that it is possible to perform quantitative ethylene (C2H4) measurements using PTR-MS. In order to demonstrate that this is possible, we need to investigate the reactions that take place in the PTR-MS with ethylene. New PTR-MS instruments allow to choose between the three primary ions H3O+, O2 + and NO+ [1], hence the name Selective Reagent Ion - Mass Spectrometry (SRI-MS). Moreover, O2 + and NO+ are the ions typically encountered in H3O+ mode and can act as parasitic, precursor ions [2,3].We performed extensive calibrations using ethylene external standards at different instrumental conditions and showed that it is possible to accurately predict ethylene concentrations by considering ethylene reaction with O2 + ions, which are found to proceed at about collision rate. We also showed that NO+ ions do not react with ethylene while for H3O+ ions the reation proceeds much below collision rate.We tested our methodology on real samples (fruits, leaves and bacteria) and compared the results with an optical ethylene sensor. A very good agreement was found. Moreover, we demostrated that SRI-MS has a broader dynamic range and a better linearity than the optical sensor