Revealing the Reactivity of Individual Chemical Entities in Complex Mixtures: the Chemistry Behind Bio-Oil Upgrading.

Bio-oils are precursors for biofuels but are highly corrosive necessitating further upgrading. Furthermore, bio-oil samples are highly complex and represent a broad range of chemistries. They are complex mixtures not simply because of the large number of poly-oxygenated compounds but because each composition can comprise many isomers with multiple functional groups. The use of hyphenated ultrahigh-resolution mass spectrometry affords the ability to separate isomeric species of complex mixtures. Here, we present for the first time, the use of this powerful analytical technique combined with chemical reactivity to gain greater insights into the reactivity of the individual isomeric species of bio-oils. A pyrolysis bio-oils and its esterified bio-oil were analyzed using gas chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry, and in-house software (KairosMS) was used for fast comparison of the hyphenated data sets. The data revealed a total of 10,368 isomers in the pyrolysis bio-oil and an increase to 18,827 isomers after esterification conditions. Furthermore, the comparison of the isomeric distribution before and after esterification provide new light on the reactivities within these complex mixtures; these reactivities would be expected to correspond with carboxylic acid, aldehyde, and ketone functional groups. Using this approach, it was possible to reveal the increased chemical complexity of bio-oils after upgrading and target detection of valuable compounds within the bio-oils. The combination of chemical reactions alongside with in-depth molecular characterization opens a new window for the understanding of the chemistry and reactivity of complex mixtures.

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-ion electrospray ionization (ESI(-)/FT-ICR MS). ESI offers selective ionization of a compound's 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 1100-3600 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 1373 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.