The Fingerprint of Essential Bio-Oils by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Six essential oils were analyzed by Fourier transform ion cyclotron resonance mass spectrometry coupled to negative electrospray ionization (ESI(-)/FT-ICR MS). ESI offers selective ionization of compounds polar functional groups containing nitrogen and oxygen heteroatoms. ESI in negative-ion mode allows the identification of the acidic compounds. The results showed that the samples contain between 1,100 – 3,600 individual molecular compositions, which corresponds to the greatest number of species detected to date in essential oils obtained from aromatic plant material. The compositions cover a mass range between m/z 150 - 500 with up to 41 carbon atoms. The dominant organic constituents of the essential oils correspond to species incorporating 2 - 5 oxygen atoms, detected as deprotonated/sodiated/chlorinated species. A set of 580 molecular assignments were found in common across all the samples, and for the first time, a set of unique molecular systems were identified, and up to 1,373 species as a unique composition for each essential oil. The molecular distributions plotted in van Krevelen diagrams (classified by their H/C vs. O/C values) suggest the presence of species with long alkyl chains and low numbers of rings plus double bonds.