Quantitative Analysis of Polar Lipids in the Nanoliter Level of Rat Serum by Liquid Chromatography/Mass Spectrometry/Mass Spectrometry

Abstract

Polar lipids in serum, including lysophospholipids (LPLs) and free fatty acids (FFAs), have a broad range of biological activities and require a suitable method for their quantitative analysis. Conventional methods use multistep procedures to simultaneously purify and analyze polar lipids and non-polar lipids in serum. However, the methods could result in inaccurate quantifications of polar and/or non-polar lipids because compounds with different polarities have different behaviors in solvent extraction and mass spectrometric ionization. In this study, a method was designed to analyze polar lipids in serum based on the polarities of LPLs and FFAs. The method consisted of extraction without filtration and analysis of the crude extract without multistep purification. Fifty LPLs and 32 FFAs were detected in rat serum. The concentrations of LPLs (1272.1 μmole/L in female and 999.8 μmole/L in male) and FFAs (1910.9 μmole/L in female and 1651.4 μmole/L in male) were determined. Peak areas of MS ion in Extract Ion Chromatogram (EIC) were used for the quantification in this study. The approach of quantification should be perfectly suitable for precise quantification of a specific serum component by adding its isotope standard to the serum before extraction.