Selective reagent ion-time of flight-mass spectrometry study of six common monoterpenes

One of the most common volatile organic compounds (VOCs) group is monoterpenes. Monoterpenes share the molecular formula C₁₀H₁₆, they are usually cyclic and have a pleasant smell. The most common monoterpenes are limonene (present in citrus fruits) and α-pinene (present in conifers’ resin). Different monoterpenes have different chemical, biological and ecological properties thus it is experimentally very important to be able to differentiate between them in real time. Real time instruments such as Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS), offer a real time solution for monoterpene measurement but at the cost of selectivity resulting in all monoterpenes being seen at the same m/z. In this work we used Selective Reagent Ion-Time of Flight-Mass Spectrometry (SRI/PTR-ToF-MS) in order to explore the differences in ion branching when different ionizations (H₃O⁺, NO⁺ and O₂ ⁺) and different drift tube reduced field energies (E/N) were used. We report a comprehensive ion library with many unique features, characteristic for individual monoterpenes.