Phospholipid Composition of Human Blood Plasma as Detected by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: New Observations

Abstract

The dependence of matrix-assisted laser desorption/ionization (MALDI) mass spectra of lipids extracted from human blood plasma and corresponding lipid compositions on different experimental conditions was studied. Not only numerous compounds of the lysophosphatidylcholines (LPCs) and phosphatidylcholines (PCs) groups, but also lipid oxidation products, including six oxidized LPCs, are detected. They are present in the original samples and produced by the reaction with air oxygen molecules, resulted in their accumulation in samples under analysis. A higher sensitivity of MALDI detection is observed for less hydrophobic LPCs as compared to more hydrophobic PCs; this phenomenon is explained. The hydrophobicity/ lipophilicity factor is also revealed in replacing the matrix of 2,5-dihydroxybenzoic acid by α-cyano-4- hydroxycinnamic acid. The latter matrix is rarely used in MALDI detection of lipids and may be suitable for the selective determination of LPCs and oxidized LPCs.