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Procedures for structural analysis of fatty acids are reviewed. The emphasis is on methods that involve gas chromatography-mass spectrometry and, in particular, the use of picolinyl ester and dimethyloxazoline derivatives. These should be considered as complementing each other, not simply as alternatives. However, additional derivatization procedures can be of value, including hydrogenation and deuteration, and preparation of dimethyl disulfide and 4-methyl-1,2,4-triazoline-3,5-dione adducts. Sometimes complex mixtures must be separated into simpler fractions prior to analysis by gas chromatography-mass spectrometry. Silver ion and reversed-phase high-performance liquid chromatography are then of special value. In particular, a novel application of the latter technique, involving a base-deactivated stationary phase and acetonitrile as mobile phase, is described that is suited to the separation of fatty acids in the form of picolinyl ester and dimethyloxazoline derivatives, as well as methyl esters.

ABSTRACT␥-Linolenic acid (GLA; C18:3 ⌬ 6,9,12 ) is a component of the seed oils of evening primrose (Oenothera spp.), borage (Borago officinalis L.), and some other plants. It is widely used as a dietary supplement and for treatment of various medical conditions. GLA is synthesized by a ⌬ 6 -fatty acid desaturase using linoleic acid (C18:2 ⌬ 9,12 ) as a substrate. To enable the production of GLA in conventional oilseeds, we have isolated a cDNA encoding the ⌬ 6 -fatty acid desaturase from developing seeds of borage and confirmed its function by expression in transgenic tobacco plants. Analysis of leaf lipids from a transformed plant demonstrated the accumulation of GLA and octadecatetraenoic acid (C18:4 ⌬ 6,9,12,15 ) to levels of 13.2% and 9.6% of the total fatty acids, respectively. The borage ⌬ 6 -fatty acid desaturase differs from other desaturase enzymes, characterized from higher plants previously, by the presence of an N-terminal domain related to cytochrome b 5 .

Sardine (Sardina pilchardus) lipids have important nutritional characteristics because of their high level of 3 fatty acids. Studies of the lipid composition of this pelagic species, studies were carried out monthly during one year. Total lipids ranged between 1.2% and 18.4% (w/w). The nonpolar lipids were dominant, mainly composed of triacylglycerols and highest in the fatty season. Phosphatidylcholine (PC), and phosphatidylethanolamine (PE) were the principal polar lipids. They were both high in 3 polyenoic fatty acids mainly 20:53 and 22:63. PC and PE were isolated and their fatty acid profiles determined; PE was higher in 22:63 than PC.

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Natural and synthetic conjugated linoleic acids (CLA) are reputed to have therapeutic properties that are specific to particular geometrical and positional isomers. Analysis of these has presented unique problems that have brought forward distinctive solutions, especially the use of gas chromatography-mass spectrometry and silver-ion high-performance liquid chromatography. In the analysis of CLA present at low levels in tissue samples, it is sometimes necessary to use concentration methods. In this review, the most useful and practical methods for the isolation and analysis of CLA isomers in tissues and in commercial CLA preparations are described.

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