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cis and trans Analysis of fatty esters by gas chromatography: Octadecenoate and octadecadienoate isomers
Author(s) -
Emken E. A.
Publication year - 1972
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02533162
Subject(s) - diastereomer , chemistry , cis–trans isomerism , peracetic acid , isomerization , structural isomer , diene , chromatography , organic chemistry , stereochemistry , catalysis , natural rubber , hydrogen peroxide
A gas chromatographic method has been developed for quantitative determination of the cis and trans percentages in octadecenoate and octadecodienoate esters. To separate cis‐ and trans ‐monoene and diene isomers on a packed GC column, the fatty esters were stereospecifically epoxipized with peracetic acid. A simple and quantitative epoxidation procedure allows the cis ‐ and trans ‐epoxyoctadecanoates to be analyzed without prior isolation from the reaction mixture. No positional or geometric isomerization of the double bond occurred during epoxidation. Synthetic mixtures containing cis ‐ and trans ‐6,‐9 and‐12 octadecenoate isomers were completely separated into cis and trans fractions trans ‐15‐Octadecenoate was the only isomer investigated that partially interfered in the analysis. Diene mixtures containing rans,trans‐, cis,trans‐ and cis,‐cis ‐9,12‐octadecadienoates were also successfully analyzed by gas liquid chromatography (GLC) after epoxidation with peracetic acid. Each diene isomer formed two pairs of diepoxy diastereomers, some of which could be separated. One cis,cis ‐diepoxyoctadecanoate diastereomer peak overlapped the cis,trans ‐diepoxyoctadecanoate peaks. The total cis,‐cis ‐diepoxyoctadecanoate percentages were calculated by using the ratio of the two cis,cis ‐diepoxyoctadecanoate diastereomers. Other positional octadecadienoate isomers were also epoxidized and analyzed by GLC. The large number of possible octadecadienoate isomers requires that some preeiminary fractionation be made before GC analysis is practical for diene isomers.