Lipidomics precursors

The novel approaches in LC-MS-based lipidomics, such as ultra-high performance LC (UHPLC), combined with high-resolution MS methodologies allow fast and reliable analysis of various classes of lipids (33). The modem instruments, with fast duty cycles, allow acquisition of high and low collision energy data simultaneously to provide both data on precursor ions and fragmentation data for all detectable molecular ions (34). 

Figure 2.2 Scan types utilized in lipidomic analysis by ESl-MS/MS. An MS/MS instrument consists of an initial mass (m/z) analyzer (MSi), a collision cell, and a second mass (m/z) analyzer (MSj). The two mass (m/z) analyzers and collision cell are separated in space on a beam instrument, such as tandem quadrupoles and Q-TOFs, and in time in ion traps. Product-ion, precursor-ion, and neutral-loss scans are performed by respectively scanning MSj, MSj, or MSj and MS2 in parallel. Multiple reaction monitoring (MRM) chromatograms are recorded with MSj and MSj fixed for transitions of interest. MS or MS/MS/MS spectra are recorded when a third mass (m/z) analyzer MS3 is utilized following a second collision cell. MS and further MS" spectra are often recorded on ion-trap instruments.

The strategy in focused lipidomics is to utilize specific fragment ions, obtained via product, precursor, or neutral loss scanning (Section 3.3.3.1), to categorize all lipids in a particular class. Specificity can be unproved with appropriate chromatographic separation, such as reversed- and normal- (hydrophilic liquid interaction chromatography (HILIC)) phase LC, as well as GC. 

Sud M, Fahy E, Cotter D, et al. LMSD LIPID MAPS structure database. Nucleic Acids Res. 2007 35 D527-D532. Tajima Y, Ishikawa M, Maekawa K, et al. Lipidomic analysis of brain tissues and plasma in a mouse model expressing mutated human amyloid precursor protein/tau for Alzheimer s disease. Lipids Health Dis. 2013 12 68. Woods AS, Jackson SN. Brain tissue lipidomics direct probing using matrix-assisted laser desorption/ ionization mass spectrometry. AAPS J. 2006 8(2) E391-395. 

---