Mass spectra of lipids

Although the focus of this report is the analysis of physiologically relevant lipid mixtures, some comments on typical patterns of MALDI-TOF mass spectra of lipids will be given on the hand of defined lipids. 

Griesinger, H., Fuchs, B., SUB, R., Matheis, K., Schultz, M., and Schiller, J. Stationary phase thickness determines the quality of thin-layer chromatography/matrix-assisted laser desorption and ionization mass spectra of lipids. Anal. Biochem., 451, 45-47, 2014. 

Figure 13.1 Distinct profiles of ethanolamine glycerophosphoUpid molecular species in lipid extracts of cognitively normal human occipital gray matter and white matter. Brain samples were obtained from the brain bank of the Washington University ADRC Neuropathology/ Tissue Resource Core, and hrain hpids were extracted hy a modified procedure of Bhgh-Dyer [1]. Negative-ion ESI mass spectra of lipid extracts of occipital gray matter (a) and white matter (b) were acquired in the presence of a small amount of LiOH as previously described [33]. Individual molecular species corresponding to each ion peak were identified using MDMS-SL analysis as previously described [34]. Plasmenylethanolamine and phos-phatidylethanolamine are abbreviated as pPE and dPE, respectively. IS denotes internal standard. Source Han [3]. Adapted with permission of Elsevier.

Markey SP, Wenger, DA. 1974. Mass spectra of complex molecules. I. Chemical ionization of sphingolipids. Chem Phys Lipids 12 182. 

Search Lipid Bank for structures and SDBS for mass spectra of common saturated fatty acids (Section 5.1.2), and identify the intense peaks with the above-mentioned characteristics. 

The analysis of simple lipids can be done with good results using common analytical methods without any need for decreasing the molecular weight of the sample by techniques such as pyrolysis. HPLC, SFC or GC procedures were applied for simple lipid analysis, and even the mass spectra of some simple triglycerides are known. As an example, Figure 8.1.1 shows the El mass spectrum of tripalmitin (standard ionization condition). 

Not only the analysis of triglycerides can be done using GC/MS. The EI+ mass spectra of other lipids with relatively small molecules are known. As an example, Figure 8.1.2 shows the mass spectrum for dipalmitoylphosphatidylethanolamine in EI+ standard conditions. 

Figure 21 Zoom scan ESI mass spectra of angiotensin II after deuteration in water (upper) and in contact with lipid vesicles (lower).

Fig. 3. Examples of mass spectra of n-hexane/dichloromethane (FI) extractable surfactants isolated by foam tower stripping from a bulk surface seawater sample (upper), an unslicked microlayer (centre), and a heavily slicked microlayer (lower). The spectra show the dominance of polyoxy components in the bulk seawater surfactants and different degrees of enrichment of more hydrophobic lipid surfactants in the microlayer. Note that these particular spectra were chosen to illustrate the range of composition observed and the impact on surface elasticity (see Figure 4), not to represent bulk seawater, unslicked and slicked microlayers generally...

Fig. 4. The variation of static surface elasticity (s0) with surface pressure (II) for air-seawater interfacial films with compositions corresponding to the FI extracts and mass spectra of Figure 3. The highest elasticities at a given film surface pressure were observed for films dominated by lipid surfactants lowest elasticities were observed for films dominated by polyoxy surfactants...

Fig. 21.3 Typical positive ion MALDI-TOF mass spectra of a chloroform-methanol extract of LDL (a) and HDL (b). The insert emphasizes the most relevant mass range of the FIDL sample. The peak labeled with an asterisk is caused by the matrix. Reprinted with modification from Journal of Lipid Research 42 (2001) 1501-1508...

The interpretation of mass spectra of common wax components are described elsewhere (Hamilton, 1995b Evershed, 1992b Christie, 1994). The mass spectra of fatty acids, alcohols, wax esters and other lipids can be found in an open access website (The AOCS Lipid Library, 2011). Briefly, the identification is performed on the basis of the characteristic fragment and molecular ions. For example, the mass spectra of saturated fatty add methyl... 

Figure 6.13 Mass spectra of products derived from 18-hydroxy-9,10-epoxy Cis acid by cleavage of lipid-derived polymers with BF3-CH3OH or UAID4. Reproduced with permission from Kolattukudy (1980).

Crawford, C. G. and Plattner, R. D. (1984) Phospholipid molecular species quantitation from mass spectra of underivatized lipids. J. Lipid Res.y 25, 518-22. 

Ferretti, A. and Flanagan, V. P. (1994) Mass spectra of piperidine and trimethylsilyl ester derivatives of the major metabolite prostaglandin F. Chem. Phys. Lipids, 74, 65-72. 

The positive-ion MALDI-TOF mass spectra of brain are dominated by PC, LPC and SM, whereas PI is the most abundant negatively charged PL. In order to be able to detect further lipid species, however, a previous separation of the total brain extract into the individual lipid classes is necessary [88]. Because of the rapid performance and simple equipment involved, TLC can be used advantageously when only small amounts of lipids are necessary for subsequent analysis by MS [132]. Indeed, by using a careful sample preparation and suitable TLC conditions, even minor glycolipids can be detected and investigated [133]. 

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