Fragmentation Patterns of Glycerolipids

Ether or vinyl ether-linked species in mono-, di-, and triglycerides are usually present in low abundance [2,3]. Therefore, unless the fragmentation patterns of these ether-linked glycerides are well characterized, only the patterns of their ester-linked counterparts are presented in this chapter. Similarly, among glycolipid species, the patterns of glycosyl DAG species that are the most characterized are discussed in the chapter. 

and triglyceride species cannot readily be ionized by protonation from nonaqueous solutions, even in the presence of organic acids (e.g., formic acid, acetic acid) under ESI conditions [4]. However, these species can be readily ionized as their adducts of ammonium, lithium, sodium, etc. (i.e., [M- -X +, A=NH4, Li, Na,. ..) in the positive-ion mode [3-11]. Similar to the glycerophospholipids as discussed in Chapter 7, an appropriate modifier has to be added to the lipid solution to form one of these kinds of adducts. If more than one modifiers are present in the lipid solution, ionization as their adducts depends on the concentrations as well as their 

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

Since a prominent charge site is absent in the glyceride species, the structure of FA substituent(s) significantly contributes to their ionization, particularly in the case of sodium adducts [10]. Therefore, the instrument response factors for ionization of these glyceride species as ammonium and alkaline adducts are apparently very different, depending on both the number of carbon atoms and of double bonds in the FA chains [10], 

Derivatization has been widely used to enhance the ionization efficiency and selectivity of mono- and diglyceride species in order to be sensitively and specifically analyzed by ESI-MS [12-14]. The fragmentation features of the derivatized mono-and diglyceride species are mentioned in the chapter if they are available. 

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The following are a few examples to demonstrate how an elucidated fragmentation pattern can be used for identification of individual species of a lipid class present in biological samples by MDMS-SL. These examples well represent different lipid classes (e.g glycerophospholipids, sphingolipid, and glycerolipids), different mass levels (from low abundance to abundance), different polarities (Ifom polar to non-polar), etc. 

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