Gas Chromatography of Fatty Acid Methyl Esters: Isolation of Geometrical Isomers by Silver-Ion Chromatography
Silver-ion chromatography is a very efficient method to purify fatty acid methyl ester (FAME) geometrical isomers before their resolution by GC. The method is based on the reversible formation of a weak charge-transfer complex between a silver ion and a double bond. A sigma bond can be formed between the silver ion and the pi electrons of double bonds; cis ethylenic double bonds form a stronger bond than trans bonds. The strength of the complex depends on the accessibility of the electrons in the orbitals as well as on steric hindrance (Cruz-Hernandez and Kramer 2007). Depending on the structure of the fatty acid moieties (chain length, number, configuration and position of double bonds), lipid species are retained for a specific time on the surface of the stationary phase.
Method based on silver-ion thin-layer chromatography (Ag+-TLC) in tandem with GC has been proved to be the best way to obtain a complete identification and analysis of the 18:1 FAME...
KeywordsDouble Bond Fatty Acid Methyl Ester Methyl Oleate Fatty Acid Ester Geometrical Isomer
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