Rapid and comprehensive evaluation of microalgal fatty acids via untargeted gas chromatography and time-of-flight mass spectrometry.

Due to their high triacylglyceride content, microalgae are intensively investigated for bio-economy and food applications. However, lipid analysis is a laborious task incorporating extraction, transesterification and typically gas chromatographic measurement. Co-elution induces a significant risk of fatty acid misidentification and thus, additional purification steps like thin layer chromatography are needed. Contrary to database matching approaches, solely targeted analysis is facilitated as compound identification is driven by matching retention times or indices with standard substances. In this context, a rapid workflow for the analysis of algal fatty acids is presented. In-situ transesterification was used to simplify sample preparation and conditions were optimized towards fast processing. If results are needed at the very day of sampling, direct processing without a preceding drying step is feasible to obtain a rough estimate about the occurrence of the major compounds. Coupling gas chromatography and time-of-flight mass spectrometry enables untargeted analysis. Unknown compounds may be identified by structural reconstruction of their respective fragmentation patterns and by database matching to routinely avoid mismatches by co-elution of disturbing agents. The developed workflow was successfully applied to derive the exact stereochemistry of all fatty acids from Chlorella vulgaris and a systematic shift depending on physiological state of the cells was confirmed.