Examining the collision‐induced decomposition spectra of ammoniated triglycerides as a function of fatty acid chain length and degree of unsaturation. I. The OXO/YOY series

Abstract

A series of positionally pure triglycerides (TAGs) of the form OXO and YOY, where O is the oleate moiety and X and Y are large arrays of different fatty acid moieties, was synthesized and analyzed by reversed-phase high-performance liquid chromatography/tandem mass spectrometry. The intensities of the collision-induced decomposition (CID) products of ammoniated TAGs (ammonium ion adducts) were examined as a function of chain length, degree of unsaturation, double-bond position, and cis/trans configuration of X and Y. The major CID products, the diglyceride fragment ions and the MH+ ion, were plotted as functions of chain length for the saturated and mono-unsaturated series of X and Y. Different trends for each of these series were observed. Trends in the abundances of these fragment ions were also characterized as a function of degree of unsaturation in the TAGs. In general, the fractional abundances of the MH+ ions vary linearly with degree of unsaturation. However, the presence of double bonds positioned close to the carbonyl carbon of the fatty acid chain promotes the formation of the diglyceride fragment ion corresponding to loss of that fatty acid. Mechanisms of the formation and decomposition of ammoniated TAGs are proposed that fit the trends observed in the data. Extensions of this work are described, and a vision of a derived library of CID spectra is discussed as a platform for comprehensive analysis of complex TAG mixtures.

Detection of the abundance of diacylglycerol and triacylglycerol molecular species in cells using neutral loss mass spectrometry

“…Much of our present understanding of the role of TAGs comes from measurement of either the total quantity of TAG present in cells, or fatty acids that can be released from TAGs after isolation and saponification rather than knowledge of changes in unique TAG molecular species. In recent years there has been renewed interest in the development of mass spectrometric methods using electrospray ionization and atmospheric pressure chemical ionization to analyze TAGs at the molecular species level [16][17][18][19]. We recently reported a strategy using MS 3 to analyze TAGs from a complex mixture as the NH 4 + adduct ions generated by electrospray ionization [20].…”

Theory and Practice of UHPLC and UHPLC–MS

“…Their range is limited and prices are rather high for small amounts probably because of difficult preparative isolation. For this reason, Evans et al (Li and Evans, 2005) have developed a synthetic procedure for regioisomeric TG starting from regioisomerically pure 1,3-diacylglycerols or 2-monoacylglycerols dissolved in chloroform, then 4-dimethylaminopyridine and selected FA chlorides are added dropwise with continuous stirring for 30 min, which yields pure TG regioisomers. This procedure has been used for synthesis of a wide range of regioisomeric series OXO/YOY (Li and Evans, 2005), PXP/YPY (Li et al, 2006), LXL/YLY, and AXA/YAY (Gakwaya et al, 2007), where X and Y are saturated FAs from C4:0 to C24:0 and unsaturated FAs containing one to six DBs.…”

“…Mass spectra of TG provide two basic types of ions sufficient for the structural assignment (Byrdwell et al, 1996;Mottram et al, 1997;: (1) molecular adducts with protons (2) Mottram et al, 1997Mottram et al, , 2001, electrospray ionization (Malone and Evans, 2004;Li and Evans, 2005;Li et al, 2006;Gakwaya et al, 2007;Herrera et al, 2010;Leveque et al, 2010), and matrix-assisted laser desorption/ionization (Pittenauer and Allmaier, 2009 Mottram et al, 1997Mottram et al, , 2001Holcapek et al, , 2005Cvacka et al, 2006;Lísa et al, 2007aLísa et al, ,b, 2009aLeskinen et al, 2008), as illustrated in the example of regioisomers SLnO/SOLn/OSLn in Fig. 4.8.…”

“…4.8. The simple approach just determines the prevailing FAs in the middle sn-2 position based on the lower relative abundance of the corresponding [M þ HeR i COOH] þ fragment ion Mottram et al, 1997Mottram et al, , 2001Dugo et al, 2004;Lísa and Holcapek, 2008), but the type of FAs (mainly DB number and positions) (Holcapek et al, 2005;Li and Evans, 2005;Li et al, 2006;Gakwaya et al, 2007) also affects relative abundances of corresponding [M þ HeR i COOH] þ fragment ions. An interesting example of the strong effect of DB position is the ratio of […”

Differential sensing for the regio- and stereoselective identification and quantitation of glycerides

“…Furthermore, the ability of a glyceride to be ionized using these methods often varies. For example, ion abundance generally increases with increasing number of double bonds in the fatty acid alkyl chain and can also depend on fatty acid alkyl chain length (21). These significant variations in ion abundance mean that ionization methodologies must be developed and tailored to a specific application to satisfactorily detect each glyceride of interest (19).…”