Abstract
Electron impact excitation of ions from organics (EIEIO), also referred to as electron-induced dissociation, was applied to singly charged SM molecular species in the gas phase. Using ESI and a quadrupole TOF mass spectrometer equipped with an electron-ion reaction device, we found that SMs fragmented sufficiently to identify their lipid class, acyl group structure, and the location of double bond(s). Using this technique, nearly 200 SM molecular species were found in four natural lipid extracts: bovine milk, porcine brain, chicken egg yolk, and bovine heart. In addition to the most common backbone, d18:1, sphingosines with a range of carbon chain lengths, sphingadienes, and some sphinganine backbones were also detected. Modifications in natural SMs were also identified, including addition of iodine/methanol across a carbon-carbon double bond. This unparalleled new approach to SM analysis using EIEIO-MS shows promise as a unique and powerful tool for structural characterization.
Highlights
Electron impact excitation of ions from organics (EIEIO), referred to as electron-induced dissociation, was applied to singly charged SM molecular species in the gas phase
EIEIO (KEe = 10 eV) was applied to a synthetic standard, SM(d18:1,12:0) (Fig. 2A), and the resulting spectrum was rich enough in diagnostic fragment ions to provide near complete structural characterization for this SM molecular species
Optimization of the kinetic energy of the electron beam (KEe) utilized for EIEIO The selection of the optimum level of KEe was essential for SM analysis using EIEIO, as we observed during our study on PCs [8]
Summary
Electron impact excitation of ions from organics (EIEIO), referred to as electron-induced dissociation, was applied to singly charged SM molecular species in the gas phase. Using ESI and a quadrupole TOF mass spectrometer equipped with an electron-ion reaction device, we found that SMs fragmented sufficiently to identify their lipid class, acyl group structure, and the location of double bond(s). Using this technique, nearly 200 SM molecular species were found in four natural lipid extracts: bovine milk, porcine brain, chicken egg yolk, and bovine heart. Using EIEIO to fragment glycerophospholipids, information regarding lipid class (or head group), acyl chain length, the number and location of double bonds, and the regioisomeric structure were obtained in a single experiment in the positive ion mode.
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