Metabolites were identified based on a comparison of retention time and mass spectrum to an authentic standard analysed under identical conditions following guidelines of the Metabolomics Standards Initiative (level 1) (Sumner et al., 2007 (link)).
Elemental compositions of putative structures were calculated using the SmartFormula tool from the DataAnalysis 4.0 software (Bruker Daltonics GmbH, Bremen, Germany), which provides a ranking according to the best fit of measured and theoretical isotopic pattern within a specific mass accuracy window. The quality of the isotopic fit was expressed by the mSigma-value. For level 2 identification (Sumner et al., 2007 (link)), a number of databases were used to search for the structural identity of the metabolites and these included; the human metabolome database (http://www.hmdb.ca/ ), the Kegg ligand database (http://www.genome.jp/kegg/ligand.html ), the BiGG database (http://bigg.ucsd.edu/ ), the PubChem database (http://pubchem.ncbi.nlm.nih.gov/ ), the LIPID MAPS database (http://www.lipidmaps.org/ ), the MassBank database (http://www.massbank.jp ) and the Metlin database (http://metlin.scripps.edu ).
Elemental compositions of putative structures were calculated using the SmartFormula tool from the DataAnalysis 4.0 software (Bruker Daltonics GmbH, Bremen, Germany), which provides a ranking according to the best fit of measured and theoretical isotopic pattern within a specific mass accuracy window. The quality of the isotopic fit was expressed by the mSigma-value. For level 2 identification (Sumner et al., 2007 (link)), a number of databases were used to search for the structural identity of the metabolites and these included; the human metabolome database (