Trihydroxy long-chain bases in bovine milk sphingomyelin

Comprehensive shotgun lipidomics of human meibomian gland secretions using MS/MSall with successive switching between acquisition polarity modes

The lipid composition of human meibomian gland secretions (meibum) has been analyzed using both targeted and untargeted mass spectrometric approaches, each of which has its advantages and disadvantages. Herein we report the results of shotgun lipidomic profiling of human meibum using a new approach that combines the advantages of targeted and untargeted analyses to yield highly sensitive and comprehensive profiles. Samples containing an estimated 7-13 µg (8-16 nL) of human meibum lipids were analyzed using MS/MSall, an untargeted approach for MS/MS. Using MS/MSall with ESI and successive polarity switching, we obtained tandem mass spectra in both modes at every 1 Da step for all ions in the m/z 200-1,200 range. In approximately 12 min, a total of 2 MS spectra and 2,000 MS/MS spectra were acquired for each sample, from which targeted analysis information was extracted. This approach allowed for the comprehensive and highly sensitive detection of meibum lipids, including species low in abundance. Altogether, more than 600 unique lipid molecular species were identified in meibum, 3 times more than previously reported in untargeted analyses of meibum samples. This untargeted MS and MS/MSall approach may be extended to other biological systems for the detection of lipids with sensitivity comparable to targeted analysis.

Preparation and gas chromatographic-mass spectrometric analysis of N-acetyl-O-trimethylsilyl derivatives of long-chain base residues of natural sphingomyelin

A procedure for the preparation of long-chain base residues of egg yolk, bovine milk and bovine brain sphingomyelin was developed. The bases were converted to N-acetyl-O-trimethylsilyl (TMS) derivatives before being submitted to gas chromatography and mass spectrometry. The chromatographic profile of the milk sample was complex with thirteen peaks, whereas the profiles of brain and egg yolk long-chain bases were simple and remarkably similar.

Quantification and comparison of some natural sphingomyelins by on-line high-performance liquid chromatography/discharge-assisted thermospray mass spectrometry

Sphingomyelins obtained from bovine brain, chicken egg yolk and bovine milk fat were analysed. Separation was performed by reversed-phase high-performance liquid chromatography utilizing a binary solvent gradient consisting of n-butanol-water-1-propanol-isooctane. Detection was accomplished by light scattering and on-line discharge-assisted thermospray (plasmaspray) ionization mass spectrometry. The positive ion mass spectra exhibit prominent ions related to the amine base structure and fragments which can be utilized for identification of molecular species. The abundance of the fragments containing the fatty acid reflects relatively well the fatty acid composition of natural sphingomyelin mixtures. Bovine brain sphingomyelin has, for example, two distinctive major molecular species composed of C24:1 and C18:0 acids as indicated by the m/z 630.6 and m/z 548.5 ions, respectively. While egg yolk exhibits ions of m/z 520.6 which indicate the presence of C16:0, bovine milk sphingomyelin has several prominent ions of m/z 632.5, 618.6 and 604.7, reflecting the proportions of C24:0, C23:0 and C22:0, respectively.