Analysis of Fatty Acids by Gas Liquid Chromatography

The fatty acids (FA) of animal, plant, and microbial origin are predominantly unbranched aliphatic chains with an even number of carbon atoms and a single carboxyl group. FA can be classified as saturated, monounsaturated, or polyunsaturated (Fig. 1 ). Saturates have all single carbon-to-carbon bonds. Monounsaturates contain a single cis double bond, whereas polyunsaturates have two or more. A list of the commonly occurring natural FA in animal tissues is shown in Table 1 . In general, FA do not exist as free carboxylic acids in living cells. In animals, they are mainly esterified into membrane phospholipids (phosphoglycerides and sphingolipids) and cytosolic neutral lipids (triglycerides and cholesteryl esters). In order to analyze the FA components of cell lipids, they must first be converted into nonpolar, volatile derivatives before they can be separated and quantified by the rapid and highly sensitive technique of gas liquid chromatography (GLC).   Fig. 1.  Structural classification of fatty acids. Table 1  Nomenclature of Some Common Natural Fatty Acids

a Abbreviated fatty acid formulae showing the number of carbon atoms (e.g., 12,18,22), the number of double bonds (e.g., 0,1,4), and the position of the first double bond in relation to the n-carbon or methyl end of the molecule (e.g., n-3,n-6).