Normal phase HPLC method for combined separation of both polar and neutral lipid classes with application to lipid metabolic flux.

Three normal phase HPLC methods were produced to separate lipid classes on a PVA-Sil stationary phase including: 9 polar lipids (method 1); 13 combined polar and neutral lipids (method 2); and a combined method that further separates the neutral lipids into 2-4 subclasses based on the presence of fatty acids containing a polar functional group (e.g. hydroxyl) for a total of 20 lipid classes and subclasses separated in a single run (method 3). Polar lipids separated include: the phosphoglycerolipids PG, PE, PI, PS, PC and LPC; the galactoglycerolipids MGDG and DGDG; and a sulfoglycerolipid SQDG. Neutral lipids include TAG, DAG, and MAG classes and sub-classes containing 0-3, 0-2, and 0-1 hydroxy fatty acids, respectively. The hexane/isopropanol/methanol/aqueous system separates polar lipids without the use of chloroform such that it is suitable for radioactivity analysis by in-line flow scintillation counting. Each method was optimized using the natural lipid standards comprised of diverse molecular species that were detected by ELSD. All molecular species of each lipid class eluted together as single peak detected by ELSD. The methods were demonstrated to be suitable for resolving lipid extracts from animal, microbial, and plant sources as well as application to 14C based metabolic tracing of lipid metabolism in leaves and seeds.