ASAP-MS and DART-MS as ancillary tools for direct analysis of the lichen metabolome.

Abstract

Lichens contain unique metabolites that most often need to be characterized from a limited amount of material. While thin layer chromatography is still the preferred analysis method for most lichenologists, liquid chromatography gives a deeper insight in the lichen metabolome, but an extractive step is needed before any analysis. Therefore, ambient ionization mass spectrometry (MS) analysis of lichen samples using Atmospheric Solid Analysis Probe (ASAP) and Direct Acquisition in Real Time (DART) techniques is evaluated. We looked for a faster method to screen the metabolome by disrupting the classical workflow of analysis. Four lichens selected for their metabolic diversity were analyzed with MS; namely Evernia prunastri, Lichina pygmaea, Parmelia saxatilis, and Roccella fuciformis. ASAP and DART analyses were compared against the reference electrospray ionization with a bioinformatic process including Van Krevelen diagrams as well as the multivariate comparison of the ionization methods in positive and negative modes. Metabolite profiles obtained from DART and ASAP analyses of lichen samples are consistent with classical analyses of lichen extracts. Through an easy and rapid experiment and without any extraction solvent, a large and informative profile of lichen metabolites is obtained when using complementary ionization modes of these high resolution mass spectrometry methods. ASAP-MS and DART-MS are two ancillary methods that provide a comprehensive evaluation of the lichen metabolome.