Analysis of Long-Chain Unsaturated Fatty Acids by Ionic Liquid Gas Chromatography

Four ionic liquid (IL) columns, SLB-IL59, SLB-IL60, SLB-IL65, and SLB-IL111, were evaluated for more rapid analysis or improved resolution of long-chain methyl and ethyl esters of omega-3, omega-6, and additional positional isomeric and stereoisomeric blends of fatty acids found in fish oil, flaxseed oil, and potentially more complicated compositions. The three structurally distinct IL columns provided shorter retention times and more symmetric peak shapes for the fatty acid methyl or ethyl esters than a conventional polyethylene glycol column (PEG), resolving cis- and trans-fatty acid isomers that coeluted on the PEG column. The potential for improved resolution of fatty acid esters is important for complex food and supplement applications, where different forms of fatty acid can be incorporated. Vacuum ultraviolet detection contributed to further resolution for intricate mixtures containing cis- and trans-isomers, as exemplified in a fatty acid blend of shorter chain C18:1 esters with longer chain polyunsaturated fatty acid (PUFA) esters.