Structure and Retention Time in the Gas-liquid Chromatography of Unsaturated Fatty Acids on Polyester Substrates

Abstract

IT is generally accepted that plots of log₁₀ retention time in the gas-liquid chromatography of the longer chain normal saturated fatty acid methyl esters against the number of carbon atoms in the fatty acid chain give a straight line with both non-polar and polar substrates. On the other hand, various simple plots of similar values obtained from unsaturated fatty acid esters with polar substrates, correlating chain length or number of double bonds, yield surprisingly little information^1–4. In the course of gas-liquid chromatographic examination of the methyl esters of the fatty acids of marine oils the retention-time data of a number of identified unsaturated fatty acids examined by different workers^1,4–9, all using polyester substrates, were plotted on semilog paper against the number of carbon atoms in the fatty acid chain. Despite the fact that a number of differing polyester substrates were used, the resulting plots showed a surprising overall similarity. This suggested that the key to the relation of the plotted points lay in the structural position of the methylene-interrupted double bond systems in the fatty acid chains in the case of the polyethylenic fatty acids, and in the position of the isolated double bonds in the monoethylenic fatty acids, rather than in the type of polyester.