Examining the collision‐induced decomposition spectra of ammoniated triglycerides. III. The linoleate and arachidonate series

Abstract

A series of positionally pure triglycerides (TAGs) of the form LXL, YLY, AXA, and YAY was synthesized and analyzed by reversed-phase high-performance liquid chromatography/tandem mass spectrometry. L and A represent the linoleate and arachidate moieties, respectively, and X and Y represent large arrays of fatty acid moieties of various chain lengths, degree of unsaturations, double-bond positions, and cis/trans configurations. The abundances of the collision-induced decomposition (CID) products of ammoniated TAGs were examined as a function of these parameters. The major CID products, the diglyceride (DAG) product ions and the MH(+) ions, are plotted as functions of chain length for the saturated and monounsaturated series of X and Y. The following trends are observed in the data. TAGs with higher degrees of unsaturation tend to show greater relative abundances of MH(+) in the CID spectra of their ammoniated precursor ions. The position of the fatty acid constituents along the glycerol backbone also seems to influence the abundances of the MH(+) ion in the CID spectra of the ammoniated precursor ions. A fatty acid constituent with double bonds along the fatty acid chain positioned close to the carbonyl promotes the formation of the DAG product ion that corresponds to its loss upon CID of the ammoniated precursor ion. Linoleic acid substituents also seem to promote the formation of DAG product ions, but to a lesser extent. Data for the YAY TAGs are used to predict the abundances of the product ions in the CID spectra of ammoniated YAX TAGs. These data are discussed in context of a broader project to develop and validate software algorithims to support a platform for comprehensive analysis of complex mixtures of TAGs.

Sequential Collision- and Ozone-Induced Dissociation Enables Assignment of Relative Acyl Chain Position in Triacylglycerols

“…12,15 Further complications arise where the FA identity influences the product ion abundance. [17][18][19] Rather than relying on ion abundance ratios in CID spectra, an explicit marker ion for assigning positional isomerism in TGs is desirable. This approach was first demonstrated with high energy (> 1 keV) CID of [TG + M] + ions on a multi-sector instrument and has since been replicated on tandem time-offlight platforms.…”

Theory and Practice of UHPLC and UHPLC–MS

“…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. They report trends in ratios of fragment ions of regioisomers depending on the alkyl chain length and the DB number.…”

“…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 […”

The use of stable-isotopically labeled oleic acid to interrogate lipid assembly in vivo: assessing pharmacological effects in preclinical species

“…Because variations in the ionization effi ciency of molecular lipids with different acyl chain compositions are known (17)(18)(19), we believe that the use of labeled internal standards with acyl chain composition identical to the analyte is required for accurate quantitation. The internal standards used in the investigations reported here were as follows: for triglycerides, 100 nM 21 -triolein internal standard for triglycerides, a diheptadecanoyl internal standard for phosphatidylcholines, and a heptadecanoyl internal standard for cholesteryl esters.…”