Quantitative and positional analysis of fatty acids

As a result of steady advances made in the analytical methodology of fatty acids and glycerolipids, it is now possible to identify, quantitate, and in many instances to isolate individual molecular species of fatty acids and their glyceryl esters. Essentially complete resolution of most natural fatty acids is now possible by GLC on polar capillary columns, which are commercially available for routine application. Combinations of GLC with mass spectrometry provide identification of many unknown acids but are not necessary for work with most known acids. Likewise, GLC on polar capillary columns can provide essentially complete resolution of the diacyl-, alkylacyl-, and alkenylacyl-glycerols. Although separations of the lower molecular weight triacylglycerols are also possible, the resolution of long chain triacylglycerols would appear to be best accomplished by HPLC. Thus, HPLC on microparticulate reversed-phase columns has yielded complete resolution of the critical pairs, triplets, and quadruplets of natural long chain triacylglycerols. Provided sufficiently large fractions can be collected, a stereospecific analysis of the individual triacylglycerols or their simple mixtures should yield both positional placement and molecular association of the component fatty acids from which exact structures of the component triacylglycerols could be reconstructed. A complete separation of intact natural glycerophospholipids has also been recently demonstrated by means of HPLC, and it is possible that this technique will completely revolutionize the identification and separation of the molecular species of glycerophospholipids, although quantitation remains a problem for the time being. Also the separations have not yet been extended to the alkylacyl- and alkenylacyl-glycerophospholipids. Since the various fractions arising from HPLC may be collected, it should be possible to obtain meaningful positional analyses of fatty acids by means of specific enzymic hydrolyses. The high purity of the fractions should allow a reliable estimation of the proportions of the reverse isomers and of fully saturated triacylglycerols, which are not resolved by the chromatographic techniques. The small fractions available from HPLC will place increased importance on the microtechniques of enzymic hydrolyses and fatty acid and acylglycerol analyses. The essentially complete analyses of the molecular species of the glycerolipids made up of the common fatty acids will greatly simplify the structural analyses of membrane and lipoprotein lipids, especially if combined with automated operation and computerized data processing.(ABSTRACT TRUNCATED AT 400 WORDS)