Quality control requirements for the correct annotation of lipidomics data.

Upon low-energy CID/HCD, lipid precursors produce relatively few abundant and highly informative fragments that enable unequivocal lipid class attribution and identification of fatty acid moieties. Nonetheless, the key for correct unequivocal lipid species annotation lies in two other peculiarities of lipids that do not pertain to the interpretation of MS SP n sp spectra: (a) lipids often form more than one adduct ion in electrospray ionization; (b) all chromatographic modes exhibit a regular retention behavior of lipids, for example, the equivalent carbon number (ECN) model used for reversed-phase chromatography[8]-[10]. While double bond position, geometry, and regioisomerism have only minor influence on lipid retention, typically lipid species only elute in the retention time range expected for their ECN. Specifically, the authors relied exclusively on software-assisted lipid assignments that were not confirmed by an independent inspection of matched spectra to recognize abundant structurally unique lipid fragments. [Extracted from the article]