Separation Behavior of Octadecadienoic Acid Isomers and Identification of cis ‐ and trans ‐Isomers Using Gas Chromatography

Using a strongly polar cyanopropyl capillary column we have investigated the gas chromatography (GC) separation behaviors of 24 octadecadienoic acid methyl ester (18:2ME) isomers compared against saturated methyl stearate (18:0ME) and arachidic acid methyl ester (20:0ME), and the dependency on the GC column temperature. The 24 isomers were obtained by performing cis ‐to trans ‐isomerization of six regioisomers: five of the 18:2ME isomers were prepared by the partial reduction of methyl α‐linolenate and methyl γ‐linolenate C18 trienoic acids with different double bond positions, whereas the sixth isomer, 18:2ME (c5, c9), was obtained from a raw constituent fatty acid methyl ester (FAME) sample extracted from Japanese yew seeds. There are no reference standards commercially available for 18:2ME isomers, and in elucidating the elution order of these isomers this study should help the future identification of cis ‐ and trans ‐type of 18:2ME. We also report the identification method of cis ‐ and trans ‐type of FAME using equivalent chain lengths and attempt the identification of cis ‐ and trans ‐type of 18:2ME isomers from partially hydrogenated canola oil.