Highly unsaturated fatty acids. III. Isolation of methyl eicosapentaenoate, ethyl docosapentaenoate, and ethyl docosahexaenoate from cod liver oil esters by chromatography

Abstract

Summarya) Displacement chromatography using a charcoal‐isopropanol‐methyl behenate system has been successfully applied to the isolation of docosahexaenoic acid and ethyl docosahexaenoate from cod liver oil concentrates.b) Methyl eicosapentaenoate was isolated from cod liver oil methyl esters by combined elution chromatography on silicic acid and displacement chromatography.c) Using silicic acid as adsorbent and petroleum ether‐chloroform as solvent, ethyl docosapentaenoate was isolated from cod liver oil ethyl esters.d) With a spinning band fractionation column it was found that fractional distillation of methyl esters of cod liver oil at 0.5 mm. Hg. resulted in increasing conjugation in the distillate as the fractionation proceeded. Fractional distillation is to be avoided as a final step in purification of polyunsaturated esters.e) The end absorption of conjugated pentaenoic acids is so large at the characteristic maximum for hexaene (3,750 Å) that simultaneous equations are required for the calculation of hexaenoic and pentaenoic acids.f) Fifteen minutes of treatment with 21% KOH‐ethylene glycol at 180° is not optimum for isomerization of ethyl docosapentaenoate from cod liver oil. The optimum isomerization times for hexaenoic acids of various sources are 4 to 6 minutes, considerably different from the 15 minutes established for arachidonate.