Session: Session 3

Developments in lichen taxonomy recognition by ASAP-HRMS

Introduction : The use of references in natural product identification under Schymanski scale is a real challenge, because of the access of exact chemical structure, with acceptable yield. In this work the synthesis of monochlorinated lichexanthone leads to four isobaric isomers, known to be present in Lichens, like Lecanora alboflavida or Myriecelis antiqua, as crude material or extract.



Methodology : A method was developed and optimized to highlight discriminations of these isomers, including tandem mass spectrometry, R-Script writing and optimization and visualization with the online solution of MetaboAnalyst 6.0. Real samples with already measured contributions were used to test the method, as proof of principle. M^+., [M+H]⁺ and [M-H]^- were evaluated.



Results : Around 400 MS spectra were recorded for optimization purpose and real sample measurements. The influence of collision energy were really critical for MS/MS comparison even with a difference of some eV. By the application with real samples, PCA and PLS-DA showed rapidely the existence of well defined groups. Kiviat diagram and matrix calculation were tested to ease the estimation of the contribution, with partial aggreement with LC-UV-MS data.



Conclusion : The method exhibits its limitation on the crude material, with the desorption at the same temperature of isobaric compounds, at nominal mass and exact mass level on the M^+.. At a first glance the use of the [M-H]^- already allows to validate with a good similarity the composition proposed by LC-UV-MS. As expected the gap of sensitivity between the technologies, here UV and quadrupole  vs. orbitrap, brings new opportunities of detection and puts in frontline the huge potential of orbitrap based workflows.