Separation of <i>cis/trans</i> fatty acid isomers on gas chromatography compared to the Ag-TLC method

Abstract

RESUMENSeparación de isómeros cis/trans de ácidos grasos mediante cromatografía de gases, comparación con el método Ag-TLC.El presente estudio investiga la separación de isómeros cis/trans de ácidos grasos mediante cromatografía de gases (GC) utilizando una columna de SP2560 de 75 m y diferentes condiciones que incluyen un programa isotérmico y una programación temperatura-tiempo. La programación temperatura-tiempo mostró una mejor separación de isómeros cis / trans de los ácidos grasos C 14:1 , C 16:1 , C 18:1 , C 18:2 y C 18:3 con los ácidos grasos de cadena corta en comparación con el programa isotermo. La separación de los isómeros trans/trans de los ácidos grasos C 18:1 incluyendo ácido elaídico (C 18:1 Δ9t) y ácido vaccénico (C 18:1 Δ11t) fué difícil mediante programación temperatura-tiempo. La cromatografía en capa fina impregnada con nitrato de plata (Ag-TLC) se realizó para separar fracciones cis/trans y el análisis de la fracciones se llevó a cabo mediante GC. El análisis GC mostró co-elución de los isómeros trans del ácido graso C 18:1 . Así, el estudio muestra que una programación temperatura-tiempo en GC con columna de cianopropilo altamente polar es suficiente para resolver los ácidos grasos trans, junto con los ácidos grasos de cadena corta cuando un gran número de muestras tiene que ser analizado. PALABRAS CLAVE: Ácidos grasos trans -Cromatografía de gases -Fraccionamiento Ag-TLC -Resolución SUMMARY Separation of cis/trans fatty acids isomers on gas chromatography compared to the Ag-TLC methodThe present study investigates the separation of the cis/ trans isomers of fatty acids on the 75 m SP2560 column under different gas chromatographic (GC) conditions including an isothermal program and a time-temperature program. The time-temperature program showed improved separation of cis/trans isomers of C 14:1 , C 16:1 , C 18:1 , C 18:2 and C 18:3 fatty acids along with short chain fatty acids compared to the isothermal program. The separation of trans/trans isomers of C 18:1 fatty acids including elaidic acid (C 18:1 Δ9t) and vaccenic acid (C 18:1 Δ11t) was difficult with the time-temperature program. The thin layer chromatography impregnated with silver nitrate (Ag-TLC) method was performed to separate cis/trans fractions and GC analysis was carried out with the trans fraction. But GC analysis showed a co-elution of trans isomers of C 18:1 fatty acid. Thus the study shows that a time-temperature programmed GC method with the highly polar cyanopropyl column is sufficient to resolve trans fatty acids along with short chain fatty acids when a large number of samples has to be analyzed.

Identification of Carbon-Carbon Double Bond Stereochemistry in Unsaturated Fatty Acids by Charge-Remote Fragmentation of Fixed-Charge Derivatives

“…The most widely used approaches for FA analysis include derivatization to fatty acid methyl esters (FAMEs) to enhance volatility and subsequent separations by gas chromatography (GC), coupled with either flame ionization detection (GC-FID) or electron ionization mass spectrometry (EI-MS). − Despite their ubiquity in lipid analysis, limitations in GC resolution of FAME isomers have been reported. For example, cis -8-octadecenoate, FA 18:1 n -10­( cis ), has recently been discovered to play a role in mammalian metabolism, but is poorly resolved from the more abundant oleic acid, FA 18:1 n -9­( cis ), in conventional GC-FAME methods .…”