Major human plasma lipid classes determined by quantitative high-performance liquid chromatography, their variation and associations with phospholipid fatty acids

An HPLC method with evaporative light-scattering detection (ELSD) was optim ized and validated for the simultaneous quantitation of cholesteryl esters (CEs), triacylglycerols (TGs), free cholesterol (FC) and phosphatidylcholin e (PC) in human plasma. The separation of CEs from TGs, the most variable p lasma lipid class, was improved by speeding up the gradient steps and by in creasing the re-equilibration time between runs. The calibrations were made at levels of 0.14-14 mug lipid/injection. The intra- and inter-day precisi on values of the method ranged between 1.9 and 4.5 and 2.3-7.2% (RSD, n=6), respectively, including determinations at two concentration levels. In com parison to other lipid classes, quantitation of PC proved to be equally rep eatable despite its lowest detector response. The relative recoveries varie d from 97.0 to 110.3%, showing good accuracy of the method. The methodologi cal variation of the lipid classes covered 0.6-3.1% of their total variatio n in the study population (n=48). The CE/FC ratio showed an even closer rel ationship with phospholipid linoleic acid (18:2n-6; r=0.65, P<0.001) than w ith serum cholesterol levels, while eicosapentaenoic acid (20:5n-3) was sig nificantly associated with PC (r=0.41, P<0.01). The CE/FC ratio increased ( P<0.01) during soyabean oil substitution and the level of PC increased (P<0 .01) during cold-pressed rapeseed oil substitution. (C) 2001 Elsevier Scien ce B.V. All rights reserved.