Mass spectrometry of the phosphatidyl amino alcohols: detection of molecular species and use of low voltage spectra and metastable scanning in the elucidation of structure

Abstract

The basic fragmentation mechanisms occurring in the mass spectra of the phosphatidylcholines have been described previously, and evidence was adduced to show that many of the more abundant ions are related by electron impact-induced processes. A molecular ion was demonstrated for dioleoyl glycerylphosphorylcholine by accurate mass measurement and by metastable scanning.In the present paper, results are reported which further extend the previous work by including a more detailed investigation of “nonapparent” fragment ions for a series of phosphatidylcholines with different acyl side chains and also for a series of phosphatidyl amino alcohols of fixed acyl composition. The results demonstrate the effect of the choline quaternary nitrogen on the stability of the molecular ion, and estimates for the appropriate rate constants are given. Nitrogen-containing fragments have been demonstrated by recording spectra at low electron voltages.The work has also been extended to include natural phosphatidylcholine preparations of mixed acyl composition, and the possibility of detecting particular molecular species has been established. Quantitative estimates may be made using suitable synthetic phosphatidylcholines, and results are presented to show the variation of the molar correction factor with acyl chain length.

Keywords

• “nonapparent” fragment ions
• quaternary nitrogen
• amino alcohols
• low electron voltage
• natural mixtures