Establishment of a Direct-Injection Electron Ionization-Mass Spectrometry Metabolomics Method and Its Application to Lichen Profiling.

Direct-injection electron ionization-mass spectrometry (DI-EI-MS) is a multivariate analysis method useful for characterizing biological materials. We demonstrated the use of DI-EI-MS for metabolic profiling using several closely related lichen species: Cladonia krempelhuberi, C. gracilis, C. pseudogymnopoda, and C. ramulosa. The methodology involves conversion of total ion chromatograms to integrated chromatograms and assessment of reproducibility. The qualitative DI-EI-MS method was used to profile the major and/or minor constituents in extracts of lichen samples. It was possible to distinguish each lichen sample by altering the electron energy in DI-EI-MS and examining the resulting data using one-way analysis of variance. Previously undetectable peaks, which are easy to fragment could be revealed by varying the electron energy. Our results suggest that metabolic profiling using DI-EI-MS would be useful for discriminating between subgroups within the same species. This is the first study to report the use of DI-EI-MS in a metabolomics application.