High-resolution analysis by nano-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry for the identification of molecular species of phospholipids and their oxidized metabolites.

Nano-electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) was applied to identify the molecular species of phosphatidylethanolamine of Caenorhabditis elegans, which has a high concentration of phospholipids with a fatty acyl chain having an odd number of carbon atoms. The molecular species of diacyl phosphatidylethanolamine with one fatty acyl chain having an odd number of carbon atoms and one fatty acyl chain having an even number of carbon atoms was identified separately from alkyl-acyl phosphatidylethanolamine with an alkyl chain having an even number of carbon atoms and a fatty acyl chain having an even number of carbon atoms. Furthermore, nano-ESI-FTICRMS was applied to the direct identification of oxidized phosphatidylcholine from soybean. The mass peaks of individual molecular species of oxidative phosphatidylcholine, such as 34:3 diacyl phosphatidylcholine with peroxide (+2O) (m/z 788.544) or 34:2 diacyl phosphatidylcholine with peroxide (+2O) (m/z 790.560), can be separated from the peaks of the molecular species of the non-oxidative phospholipids. This suggests that the mass peaks with a difference of less than 0.1 mass units in their molecular weight can be separated and that their individual exact molecular compositions can be obtained by the FTICRMS analysis. The high resolution and high accuracy of FTICRMS are very effective in the analysis of molecular species of phospholipids and their derivatives.