Equivalent Carbon Number and Interclass Retention Time Conversion Enhance Lipid Identification in Untargeted Clinical Lipidomics

Chromatography is often used as a method for reducing sample complexity prior to analysis by mass spectrometry, and the use of retention time (RT) is becoming increasingly popular to add valuable supporting information in lipid identification. The RT of lipids with the same headgroup in reversed-pha...

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Bibliographic Details
Published in:Analytical chemistry (Washington) 2022-03, Vol.94 (8), p.3476-3484
Main Authors: White, Jake B, Trim, Paul J, Salagaras, Thalia, Long, Aaron, Psaltis, Peter J, Verjans, Johan W, Snel, Marten F
Format: Article
Language:English
Subjects:
Carbon
Chemistry
Conversion
Coronary artery
Equivalence
Fatty acids
Glycerophospholipids
Heart surgery
Humans
Libraries
Lipidomics
Lipids
Mass spectrometry
Mass spectroscopy
Phase separation
Plasma
Retention
Retention time
Scientific imaging
Spectroscopy
Tandem Mass Spectrometry - methods
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Summary:Chromatography is often used as a method for reducing sample complexity prior to analysis by mass spectrometry, and the use of retention time (RT) is becoming increasingly popular to add valuable supporting information in lipid identification. The RT of lipids with the same headgroup in reversed-phase separation can be predicted using the equivalent carbon number (ECN) model. This model describes the effects of acyl chain length and degree of saturation on lipid RT. For the first time, we have found a robust correlation in the chromatographic separation of lipids with different headgroups that share the same fatty acid motive. This relationship can be exploited to perform interclass RT conversion (IC-RTC) by building a model from RT measurements from lipid standards that allows the prediction of RT of one lipid subclass based on another. Here, we utilize ECN modeling and IC-RTC to build a glycerophospholipid RT library with 517 entries based on 136 tandem mass spectrometry-characterized lipid RTs from NIST SRM-1950 plasma and lipid standards. The library was tested on a patient cohort undergoing coronary artery bypass grafting surgery (n = 37). A total of 156 unique circulating glycerophospholipids were identified, of which 52 (1 LPG, 24 PE, 5 PG, 18 PI, and 9 PS) were detected with IC-RTC, thereby demonstrating the utility of this technique for the identification of lipid species not found in commercial standards.
ISSN:0003-2700
1520-6882
DOI:10.1021/acs.analchem.1c03770