Mass spectrometry of triglycerides: I. Structural effects

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. Presented in part at the AOCS Meeting, New Orleans, April 1970. Part V of a series on Mass Spectrometry of Lipids. For IV see Lipids 4:421–427 (1969).