y-Linolenic acid (6c,9c, 12c-18:3) has recently become important for dietary and pharmaceutical applications. The reported occurrence of y-linolenic acid in seed oils from plant families known to produce fatty acids, including 18:3 acids, with AS-cis and AS-trans double bonds makes it necessary to distinguish between Sc,9c,12c-, St,9c,12c-and 6~,9~,12~-octadecatrienoic acids by gas chromatography (CC) alone in routine screening operations. The separation of these acids using two different capillary GC systems has been investigated. The successful separation of octadecatrienoic acids with 5c, 5t and 6c double bonds is shown by way of gas chromatograms of the fatty acid methyl esters obtained from the seed oils of four different species of the family Ranunculaceae and of Xeranthemum and Pinus.

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SummarySeed oils from the Compositae plant family are known to contain a variety of unusual fatty acids. Subsequent to the recent discovery of c-linolenic acid in Saussurea and Youngia, further Mongolian Compositae species were investigated for their seed oil fatty acid composition. A number of D3trans-fatty acids (16 : 1D3t, 18 : 1D3t and 18 : 3D3t, 9c, 12c) were found in the seed oils of Heteropappus hispidus and Asterothamnus centrali-asiaticus. The latter fatty acid, but not the trans-monoenes, was also found in one species of Artemisia. These unusual fatty acid isomers were characterized by capillary gas-liquid chromatographic (GLC) separations in combination with other chromatographic techniques (analytical thin layer chromatography, TLC and preparative argentation TLC), and infrared spectrocsopy (IR). Their identity was further confirmed by co-chromatography with other seed oils known to contain these trans-fatty acids. The fact that within the Compositae plant family there are apparently two or three distinct groups of genera containing D3trans-fatty acids is discussed.