A reliable analysis of tissue free fatty acids by gas-liquid chromatography

A convenient and reliable gas-liquid chromatographic method for determining the free fatty acids in biological specimens is described. The free fatty acids were extracted with hexane in the presence of H3PO4 and then back-extracted from the hexane phase into a very small volume of trimethyl (alpha, alpha, alpha-trifluoro-m-tolyl)ammonium hydroxide solution. Direct injection of the resultant quaternary ammonium salts of the fatty acids into a gas-liquid chromatograph unit gave their methyl esters, with a high recovery. The presence of triglycerides, phospholipids, or cholesterol esters did not interfere with the determination of free fatty acids. This method was applied to determination of free fatty acids in the samples of serum or brain. The results were more precise and reliable than those reported with the conventional methods with TLC separation. This method should be a useful aid for providing precise information about the physiological or pathological roles of free fatty acids.