Gas-liquid chromatographic profiling of plasma lipids using high-temperature-polarizable capillary columns

We have examined the potential usefulness in plasma lipid profiling of capillary columns coated with a high-temperature-polarizable phenylmethyl silicone liquid phase, previously employed for gas-liquid chromatography (GLC) of natural triacylglycerols. The column yielded an excellent resolution for plasma triacylglycerols, cholesteryl esters and the trimethylsilyl (TMS) and tert-butyldimethylsilyl (t-BDMS) ethers of free cholesterol, as well as of the TMS and t-BDMS ethers of the diacylglycerols and ceramides released from plasma phospholipids by phospholipase C digestion. The various lipid classes were resolved into molecular species according to chain length and number of double bonds. The different molecular species were recovered in variable proportions as indicated by comparisons of peak area percentages obtained on the polar columns with those recorded on non-polar columns, which have been previously shown to give correct quantitative proportions. The cholesteryl esters are thermally degraded at high temperatures and must be eluted at as low a temperature as possible. Under the selected experimental conditions, the cholesteryl esters were found to partly interdigitate with the triacylglycerol species of carbon numbers 46-48. The TMS and t-BDMS ethers of diacylglycerols and ceramides emerged clearly ahead of the leading triacylglycerol of the 42 acyl carbon series. However, the diacylglycerol and ceramide species overlapped and interdigitated extensively with each other. Due to low polarity below 280 degrees C, the polarizable-liquid phase was not suitable for the resolution of the molecular species of monoacylglycerols and free fatty acids, which were separated on the basis of carbon number only. Nevertheless, capillary GLC on the polarizable liquid phases provides a novel and informative profiling of plasma lipids, the application of which to the assay of plasma lipid abnormalities deserves further examination.