Flow Field-Flow Fractionation with Mass Spectrometry for Top-Down and Bottom-Up Lipidomics

As lipidomics has attracted increased attention in life science, advanced mass spectrometry (MS) technologies have been combined with other separation techniques to improve and expand the branch of study. This review intends to provide general knowledge of offline and online coupling of flow field-flow fractionation (FlFFF)—a technique that encompasses the separation of nano- to micro-scale biomolecules—with MS for analysis of blood plasma lipoproteins, processes that are considered bottom-up and top-down approaches, respectively. The first part of this review focuses on the bottom-up method using multiplexed hollow fiber FlFFF (MxHF5) and nanoflow liquid chromatography electrospray-ionization tandem mass spectrometry (nLC-ESI–MS/MS) for non-targeted identification of lipids. In this protocol, plasma lipoproteins of different types are collected using MxHF5, and the lipids within the lipoproteins are then extracted and analyzed via nLC-ESI–MS/MS. The second part of the review describes the top-down approach, which uses online coupling of miniaturized FlFFF to ESI–MS for a fast screening of targeted lipids. Here, the separation of lipoproteins and detection of their component lipids are achieved simultaneously. While both methods aim to quantify the lipids within lipoproteins, the bottom-up approach provides an extensive lipidome, whereas the top-down method is suitable for high-speed targeted lipidomic analysis. This review discusses variants of FlFFF-ESI–MS/MS that offer effective analytical technologies for lipidomics.