Separation of 20:4n-6 and 20:4n-7 by capillary gas-liquid chromatography

The use of a capillary column coated with 100% cyanopropyl polysiloxane (CP(TM)Sil 88) allows the separation of several fatty acids associated with fat deficiency. Starting with liver mitochondrial phospholipids of weanling rats fed a fat-free diet, an unusual fatty acid was isolated, along with 20:4n-6, by thin-layer chromatography on AgNO3-impregnated silica gel plates. After partial hydrazine reduction of these acids, the resulting monoenes were isolated and subjected to ozonolysis in BF3/methanol. The resulting monomethyl and dimethyl esters were identified by gas chromatography/mass spectrometry. Our data indicate that the unusual component corresponds to 20:4n-7. Based on published biochemical and analytical studies and on our own chromatographic retention data, some of the other unusual fatty acids were tentatively identified as 18:2n-7, 20:2n-7 and 20:3n-7. The CP(TM)Sil 88 column appears to be a simple and useful tool for the separation of fatty acids of the palmitoleate series.