Application of methoxy‐bromomercuri‐adduct fractionation to the analysis of fatty acids of partially hydrogenated marine oils

The fatty acids of a refined and of a partially hydrogenated menhaden oil, iodine value (IV) 84.5, were separated into different classes (e.g., monoene, diene, including pentaene and hexaene) by thin layer chromatography (TLC) of their methoxy‐bromomercuri‐adducts (MBM). In the solvent system hexane: dioxane, the separation of fatty acids occurred according to the degree of unsaturation. No influence was exerted by either the geometry or the position of the ethylenic bonds. The effect of the various chain lengths (C 14 −C 22 ) was to broaden the bands, but no overlap occurred among the chain lengths. A wide range of C 20 unsaturated fatty acids were prepared by the hydrazine reduction of 20∶5‐Δ5,8,11,14,17. These were separated into groups as MBM adducts and identified by comparison of their experimental and calculated equivalent chain lengths (ECL) in gas liquid chromatography (GLC) on SILAR‐5CP and SILAR‐7CP columns. This confirmed that GLC did not totally separate all groups of isomers of different degrees of unsaturation. The quantitative analysis of both refined and partially hydrogenated (IV‐84.5) menhaden oils by GLC was effected by the recovery of the fatty acid methyl esters from the MBM adduct TLC bands with the addition of methyl heptadecanoate (17∶0) as an internal standard, followed by analysis of the different fractions on open‐tubular columns coated with SILAR‐5CP. For methylene‐ and nonmethylene‐interrupted unsaturated acids, 100% recovery from the MBM adducts was achieved, but in the case of the conjugated dienes the maximal recovery was 70%.