A critical assessment of different transmethylation procedures commonly employed in the fatty acid analysis of aquatic organisms

Several transmethylation procedures have been used for fatty acid analysis of aquatic organisms, although the suitability of the applied procedures has rarely been tested. The aim of this study was to demonstrate how different derivatization procedures can affect the result of fatty acid analysis. Different transmethylation procedures based on the acidic catalysts boron trifluoride, concentrated sulphuric acid, and anhydrous hydrochloric acid were applied to cold-pressed copepod oil and Atlantic salmon flesh lipids rich in wax esters and triacylglycerols, respectively. The results show that (1) the use of unsuitable catalysts and/or incubation conditions may influence the data obtained, which can lead to inaccurate conclusions about the presence of fatty acids in aquatic organisms/ecosystems, (2) different derivatization procedures based on the same catalyst can produce diverging results, and (3) the efficiency of a selected catalyst/procedure should be verified (e. g., by thin-layer chromatography) to ensure the complete transmethylation of fatty acids.