GC-FID analysis of FAMEs
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The GC analysis of fatty acid methyl esters (FAMEs) is a significant analytical technique for the characterization of lipid fraction and composition of individual fatty acids in foods or biological samples. Knowing the composition of fats is essential for nutrition purposes. The composition of fats is a complex mixture of various carbon chain length saturated and unsaturated fatty acids esters of glycerol, mainly triglycerides. The structure of lipids in biological samples is far more diverse than in fats. As the biochemical roles of fatty acids vary depending on their structure, it is important to determine the composition of individual fatty acids in biological samples.
In our laboratory, the primary and routine analytical technique for qualitative and quantitative analysis of FAMEs is the GC-FID equipped with the DB-23 column (Agilent). Many fatty acids can be separated on polyethylene glycol (PEG) capillary columns however, some cis-trans isomers cannot be differentiated on PEG columns, and therefore cyanopropyl (DB-23) stationary phase is preferred. For challenging cases, the GC-MS or GC-(CI)MS analysis may be employed.
Transmethylation of fatty acids can be carried out either upon basic (KOH/methanol) or acidic (HCl/methanol) catalysis. Only esters of fatty acids can be transmethylated upon the base catalysis, while all fatty acids (also free) can be methylated in HCl/methanol media. For the semi-quantitative analysis, an atypical fatty acid (usually C17:0) can be added as an internal standard.
The GC-FID chromatogram of Food FAMEs standard mix (column: DB-23, Agilent).
The GC-FID chromatogram of Marine Oil FAMEs standard mix (column: DB-23, Agilent).
The elution order of FAMEs was first determined using the GC-MS.
The GC-MS isobutane-CI chromatogram of Food FAMEs standard mix (column: DB-23, Agilent. GC-MS, - Polaris Q (Thermo Scientific)).
FAMEs can also be analyzed using the WAX GC columns though some FAMEs cannot be fully separated.
The GC-MS isobutane-CI chromatogram of Food FAMEs standard mix (column: SolGel-WAX, SGE).
GC-MS electron ionization (EI) is not the optional technique for the analysis of unsaturated FAMEs since molecular ions are not stable and such compounds cannot be unequivocally determined. The GC-MS CI (chemical ionization), a milder ionization method, is a more advantageous method for the analysis of unstable compounds.
Saturated FAMEs can be successfully analyzed using both, GC-MS (EI) and GC-MS (CI).
GC-FID chromatogram of FAMEs detected in human milk.
Results of this application were published in "Amelioration of diabesity-induced colorectal ontogenesis by omega-3 fatty acids in mice", February 2012, Journal of Lipid Research 53(6):1056-70.
Structures and names of fatty acids commonly used in food industry
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