Preparation, isolation and identification of non-conjugated C18:2 fatty acid isomers

Abstract Non-conjugated geometric/positional isomers of linoleic acid ( c 9, c 12-18:2) are often present in processed foods and oils. The following work presents a simple addition/elimination reaction for preparation of non-conjugated 18:2 fatty acid isomers. A mixture containing positional and geometric isomers of C18:2 fatty acids was produced by addition of hydrobromic acid to the fatty acid double bonds, followed by its elimination with a strong sterically hindered base. Pure 8,12-, 8,13-, 9,12-, and 9,13-18:2 fatty acid methyl esters were isolated from the synthetic mixture by a combination of sub-ambient RP-HPLC and Ag + -HPLC. The determination of the double bond position was achieved by GC–MS using picolinyl esters derivatives. The determination of the fatty acid double bond geometric configuration was obtained by partial hydrogenation of the isolated isomer with hydrazine, followed by the GC-FID analysis.