title: On Mass Ambiguities in High-Resolution Shotgun Lipidomics.
abstract: Mass-spectrometry-based lipidomics aims to identify as many lipid species as possible from complex biological samples. Due to the large combinatorial search space, unambiguous identification of lipid species is far from trivial. Mass ambiguities are common in direct-injection shotgun experiments, where an orthogonal separation (e.g., liquid chromatography) is missing. Using the rich information within available lipid databases, we generated a comprehensive rule set describing mass ambiguities, while taking into consideration the resolving power (and its decay) of different mass analyzers. Importantly, common adduct species and isotopic peaks are accounted for and are shown to play a major role, both for perfect mass overlaps due to identical sum formulas and resolvable mass overlaps. We identified known and hitherto unknown mass ambiguities in high- and ultrahigh resolution data, while also ranking lipid classes by their propensity to cause ambiguities. On the basis of this new set of ambiguity rules, guidelines and recommendations for experimentalists and software developers of what constitutes a solid lipid identification in both MS and MS/MS were suggested. For researchers new to the field, our results are a compact source of ambiguities which should be accounted for. These new findings also have implications for the selection of internal standards, peaks used for internal mass calibration, optimal choice of instrument resolution, and sample preparation, for example, in regard to adduct ion formation.
authors.affiliation: Berlin Institute of Health Technology Platform Metabolomics, Max-Delbrück-Centrum for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.
authors.forename: Chris
authors.identifier: 0000-0001-5756-3988
authors.initials: C
authors.lastname: Bielow
authors.affiliation: Berlin Institute for Medical Systems Biology, Max-Delbrück-Centrum for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Mastrobuoni
authors.affiliation: Berlin Institute for Medical Systems Biology, Max-Delbrück-Centrum for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.
authors.forename: Marica
authors.initials: M
authors.lastname: Orioli
authors.affiliation: Berlin Institute of Health Technology Platform Metabolomics, Max-Delbrück-Centrum for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.|Berlin Institute for Medical Systems Biology, Max-Delbrück-Centrum for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kempa
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D016208:Databases, Factual; D008055:Lipids / Q000032:analysis* / Q000097:blood; D008099:Liver / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D008055:Lipids; D012964:Sodium