Mass Spectrometry-Based Lipidomics Approaches

In this chapter, the lipidomics approaches developed based on the electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) technologies (see Chapter 2) are described. Although matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has played many important roles in lipidomics and is also discussed in the chapter, it is no doubt that the majority of the platforms for lipidomics analysis currently used are based on ESI-MS in conjunction with MS/MS analyses. 

Ions are generated in an electrospray ion source after a stream of lipid solution is pushed into the ion source chamber by a mechanical force (see Chapter 2). Depending on whether lipid analysis conducted with the lipid solution delivered to the ion source chamber is under a constant lipid concentration condition, these ESI-MS-based lipidomics approaches can be classified into two major categories  

Lipidomics Comprehensive Mass Spectrometry cf Lipids, First Edition. Xianlin Han. 2016 John Wiley Sons, Inc. Published 2016 by John Wiley Sons, Inc. 

---

In the high mass accuracy/resolution mass spectrometry-based shotgun lipidomics approach, the overlaps between SM and M-f1 C isotopologue of PC species, and between PC subclasses can be resolved [35]. Moreover, the linkages of alkyl vs. alkenyl at the sn-1 position of glycerol and the fatty acyl chains of diacyl species are also identified by product-ion analysis [35,36]. Clearly, this approach provides much more structural information than that of the tandem MS approach as aforementioned. 

To reflect these different levels of structural information, a system of shorthand notation for lipid structures derived from MS analysis was proposed [39] and becomes widely accepted. For example, for analysis of PC species, it was proposed to notate with PC(nominal mass) or PC(m n) to represent a detected species by the tandem MS approach (where m and n are the total number of carbon atoms and double bonds of aliphatic chains in the species, respectively) with PC(mi i i2 2) or PC(o-mi ni m2 2) to reflect the identification of individual fatty acyl chains and the ether bond by the high mass resolution mass spectrometry-based shotgun lipidomics and with VCim1.n1lm2.n2) or VCio-m1.n1lm2.n2) to denote the total identification of PC species by MDMS-SL. Similarly, MRM-based methods after... 

As the development of lipidomics field, mass spectrometric analysis of plant lipids has been advanced accordingly. The branch of lipidomics in analysis of plant cellular lipids utilizing mass spectrometry was specifically called plant lipidomics [1], As described early in the book (Chapter 3), all kinds of MS-based lipidomics approaches, particularly those based on ESl-MS or ESI-MS/MS, could be used in plant lipidomics. The advantages of ESl-MS-based methods over traditional lipid analytical approaches for analysis of plant lipids were extensively discussed [1-3]. 

---