Top-down lignomics analysis of the French oak lignin by atmospheric pressure photoionization and electrospray ionization quadrupole time-of-flight tandem mass spectrometry: Identification of a novel series of lignans.

We report herein the top-down lignomic analysis of virgin released lignin (VRL) extracted from the French oak wood using atmospheric pressure photoionization quadrupole orthogonal time-of-flight mass spectrometry (APPI-QqTOF-MS) (+ ion mode). Eight major protonated lignin oligomers were identified using the APPI-QqTOF-MS/MS of this complex VRL mixture without any kind of purification. This series of protonated oligomer ions were identified as neolignan cedrusin (1), five different aryltetralin lignans dimers (2-6), one lignan-dehydroshikimic acid complex (7), and a lignan trimer (8). Similarly, electrospray ionization (ESI)-QqTOF-MS (+ ion mode) allowed us to identify three extra aryltetralin lignan derivatives (9-11). The Kendrick mass defect analysis was used for the simplification of this complex APPI-QqTOF-MS into a compositional map, which displayed clustering points of associated ions possessing analogous elemental composition. This series of novel protonated molecules were selected and subjected to low-energy collision-induced dissociation (CID)-MS/MS analyses. The obtained gas-phase fragmentation patterns helped to tentatively assign their most likely structures. Also, it was found that the use of different APPI and ESI ambient ionization techniques enhances the ionization of different types of lignin oligomers.