Mass spectrometry of triglycerides: I. Structural effects
TL;DR: Evidence which indicates the possibility of determining the location of unsaturation by the interruption of homology of the [RCO+128+14n]+ series, brought about by the addition of deuterium to the unsaturated linkages, is introduced.
Abstract: Mass spectra of several triglycerides of specific structure or with specific deuterium labeling have been measured with a low resolution mass spectrometer. With saturated triglycerides the abundances of ions characteristic of the component acids, [M-RCO2]+, increase with increasing chain length, and [M-RCO2CH2]+ decrease with increasing chain length. Unsaturation in the acyl moiety causes the abundant formation of [RCO-1]+. Structures have been suggested for a number of the main peaks obtained from saturated triglycerides, and high resolution spectra of one triglyceride agree with the postulated structures. The peaks, [RCO+74]+, [RCO+115]+ and [RCO+128+14n]+, represent structures which contain the glyceryl portion of the triglyceride, since in case of the replacement of its hydrogens with deuteriums, these peaks are shifted accordingly. Evidence which indicates the possibility of determining the location of unsaturation by the interruption of homology of the [RCO+128+14n]+ series, brought about by the addition of deuterium to the unsaturated linkages, is introduced. Further evidence is also presented, which indicates that the [M-RCO2CH2]+ ions arise from the positions 1 and 3 and, in agreement with earlier studies from other laboratories, it is thus possible to identify the acyl groups attached to the 1 and 2 positions of the glyceryl moiety.
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TL;DR: ESI-MS and APCI-MS were found to be complementary techniques, which together contributed to a better understanding of the identities of the products formed by oxidation of triacylglycerols.
Abstract: Two mass spectrometers, in parallel, were employed simultaneously for analysis of triacylglycerols in canola oil, for analysis of triolein oxidation products, and for analysis of triacylglycerol positional isomers separated using reversed-phase high-performance liquid chromatography. A triple quadrupole mass spectrometer was interfaced via an atmospheric pressure chemical ionization (APCI) interface to two reversed-phase liquid chromatographic columns in series. An ion trap mass spectrometer was coupled to the same two columns using an electrospray ionization (ESI) interface, with ammonium formate added as electrolyte. Electrospray ionization mass spectrometry (ESI-MS) under these conditions produced abundant ammonium adduct ions from triacylglycerols, which were then fragmented to produce MS/MS spectra and then fragmented further to produce MS/MS/MS spectra. ESI-MS/MS of the ammoniated adduct ions gave product ion mass spectra which were similar to mass spectra obtained by APCI-MS. ESI-MS/MS produced diacylglycerol fragment ions, and additional fragmentation (MS/MS/MS) produced [RCO](+) (acylium) ions, [RCOO+58](+) ions, and other related ions which allowed assignment of individual acyl chain identities. APCI-MS of triacylglycerol oxidation products produced spectra like those reported previously using APCI-MS. APCI-MS/MS produced ions related to individual fatty acid chains. ESI-MS of triacylglycerol oxidation products produced abundant ammonium adduct ions, even for those molecules which previously produced little or no intact molecular ions under APCI-MS conditions. Fragmentation (MS/MS) of the [M+NH(4)](+) ions produced results similar to those obtained by APCI-MS. Further fragmentation (MS/MS/MS) of the diacylglycerol fragments of oxidation products provided information on the oxidized individual fatty acyl chains. ESI-MS and APCI-MS were found to be complementary techniques, which together contributed to a better understanding of the identities of the products formed by oxidation of triacylglycerols.
196 citations
TL;DR: The mass spectra of APCI mass spectrometry showed that minimal fragmentation occurs, resulting primarily in diglyceride [M−RCOO]+ ions and [M+1]+ protonated molecular ions.
Abstract: Atmospheric pressure chemical ionization (APCI) mass spectrometry was investigated as a new method for analysis of a mixture of triglycerides separated by reverse-phase high-performance liquid chromatography. A mixture of homogeneous (monoacid) triglyceride standards containing fatty acids with zero to three double bonds was analyzed to demonstrate the quality of mass spectra obtained by using the APCI interface. The mass spectra showed that minimal fragmentation occurs, resulting primarily in diglyceride [M−RCOO]+ ions and [M+1]+ protonated molecular ions. The degree of unsaturation within the acyl chains had a marked effect on the proportion of diglyceride ions vs. the [M+1]+ ions formed in the APCI source. The mass spectra of triglycerides containing fatty acids with two or three double bonds showed predominantly protonated triglyceride ions, with diglyceride peaks representing 13 to 25% of the base peak. The triglycerides containing singly unsaturated fatty acids gave diglyceride ions as the base peak, and [M+1]+ ions with an intensity 20 to 28% that of the base peak. Only diglyceride ions were observable in the spectra of triglycerides containing saturated fatty acids.
114 citations
TL;DR: The results with rearranged butterfat confirmed the validity of pancreatic lipase hydrolysis as a means of generating representative diglycerides from milk fat triglycerides and it was shown that butyric acid in the 3 position was preferentially paired with myristic, palmitic and oleic acids in the 1 position, which was also characteristic of the other short chain acids.
Abstract: The enantiomeric nature of the triglycerides of bovine milk fat was reinvestigated by determining the stereospecific distribution of fatty acids in rearranged butterfat, following partial hydrolysis with pancreatic lipase, and in certain molecular distillates of native butterfat, following Grignard degradation. The results with rearranged butterfat confirmed the validity of pancreatic lipase hydrolysis as a means of generating representative diglycerides from milk fat triglycerides. The Grignard degradation and lipolysis gave identical distributions for fatty acids when included as part of the assay system in the stereospecific analysis. Characteristically, butyric acid and the other short chain acids occupied the 3 position in the native butterfat, while in the rearranged oil they were distributed more or less randomly. Gas chromatographic analysis of the short chain glycerides on polyester columns allowed an effective resolution of butyryl, caproyl and caprylyl glycerides of identical numbers of total acyl carbons and double bonds. The method was especially well suited for resolution of the 2,3-diglycerides, which were recovered either as the more polar fraction from thin layer chromatography of the X-1,2-diacylglycerols, or by acetolysis of the residual phenolphosphatides resulting from phospholipase A digestion. It was shown that butyric acid in the 3 position was preferentially paired with myristic, palmitic and oleic acid in the 2 position, and palmitic and oleic acid in the 1 position, which was also characteristic of the other short chain acids.
102 citations
TL;DR: The effects of the traditional processing methods of linseed oil on its triacylglycerol (TAG) composition were studied, using the following analytical methods: high performance size exclusion chromatography (HPSEC), Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry (HPLC-APCI-MS).
Abstract: Different oil processing methods were performed, which included washing with water and treatment with lead-based driers, with and without heating to different temperatures, giving a set of 7 oils to be investigated. The effects of the traditional processing methods of linseed oil on its triacylglycerol (TAG) composition were studied, using the following analytical methods: high performance size exclusion chromatography (HPSEC), Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry (HPLC-APCI-MS), direct temperature resolved mass spectrometry (DTMS), matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), and electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). A decrease of the initial cis-double bonds and the formation of trans-double bonds upon heating of the oils was observed. Heating a lead and oil mixture to 150°C, or heating the oil alone to 300°C led to the highest degree of oxidation. A difference was observed for the oxidation patterns for oils with and without the addition of lead. Furthermore, levels of oxygen incorporation were higher when lead was added to the oil. High temperature treatment of the oils resulted in an increased average molecular weight. The changes in the initial conformation of the double bond systems observed with FTIR were supported by HPLC-APCI-MS measurements that showed the formation of a number of new isomeric TAGs in the heated oil compared to freshly pressed, untreated oil. Oligomerisation up to hexamers was observed with HPSEC, and MALDI-TOF-MS. The formation of oligomers up to trimers only, however, was observed with ESI-FTICR-MS. Incorporation of oxygen was mainly observed with MALDI-TOF-MS and ESI-FTICR-MS whereas with DTMS and FTIR hardly any evidence was found for this.
102 citations
TL;DR: In this paper, complex mixtures of wax esters, steryl esters and triacylglycerols were analyzed using combined high resolution gas chromatography and electron impact and chemical ionization quadrupole mass spectrometry.
Abstract: Complex mixtures of wax esters, steryl esters and triacylglycerols isolated from representative biological and geochemical samples have been analyzed using combined high resolution gas chromatography and electron impact and chemical ionization quadrupole mass spectrometry. These low volatility neutral lipids containing up to 65 carbons were chromatographed intact on 15–20 m high-temperature (upper limit: 370 C) persilylated SE-52 and SE-30 glass capillary columns. Discrimination effects due to adsorptive losses and degradation were minimized using a nonvaporizing on-column injector and a direct all-glass capillary connection (370 C) to the quadrupole mass spectrometer. Structural information regarding the fatty acid and alcohol moieties was found to be maximal for methane-CI spectra in the case of wax and steryl esters, whereas EI spectra were most useful in interpreting triacylglycerol structures. Principal features of the EI and CI fragmentation patterns are discussed. The molecular composition of complex mixtures of these lipids is reconstructed for selected samples.
93 citations
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114 citations
TL;DR: The complete series of methylene-interrupted cis-cis -octadecadienoic acids (analogues of linoleic acid), from the 2,5- to 14,17-isomer, has been synthesized as discussed by the authors.
102 citations
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TL;DR: Deuterium labeled monoacid triglycerides were synthesized and their mass spectra provided further support for proposed structures of principal ions, knowledge about the formation of [M-18]+, the interexchange of hydrogen atoms between 2 and the 5,6 or 7 positions and the explusion of part of the alkyl chain.
Abstract: Deuterium labeled monoacid triglycerides were synthesized and their mass spectra were measured. The spectra provided further support for proposed (1) structures of principal ions, knowledge about the formation of [M-18]+, the interexchange of hydrogen atoms between 2 and the 5,6 or 7 positions and the explusion of part of the alkyl chain.
70 citations