Premium
Analysis of C 18:1 cis and trans fatty acid isomers by the combination of gas‐liquid chromatography of 4,4‐dimethyloxazoline derivatives and methyl esters
Author(s) -
Aro Antti,
KosmeijerSchuil Truus,
Bovenkamp Peter,
Hulshof Paul,
Zock Peter,
Katan Martijn B.
Publication year - 1998
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-998-0275-5
Subject(s) - chemistry , cis–trans isomerism , fatty acid , structural isomer , gas chromatography , chromatography , fatty acid methyl ester , thin layer chromatography , organic chemistry , catalysis , biodiesel
Trans fatty acids in foods are usually analyzed by gas‐liquid chromatography (GLC) of fatty acid methyl esters (FAME). However, this method may produce erroneously low values because of insufficient separation between cis and trans isomers. Separation can be optimized by preceding silver‐ion thin‐layer chromatography (Ag‐TLC), but this is laborious. We have developed an efficient method for the separation of 18‐carbon trans fatty acid isomers by combining GLC of FAME with GLC of fatty acid 4,4‐dimethyloxazoline (DMOX) derivatives. We validated this method against conventional GLC of FAME, with and without preceding Ag‐TLC. Fatty acid isomers were identified by comparison with standards, based on retention times and mass spectrometry. Analysis of DMOX derivatives allowed the 13 t , 14 t , and 15 t isomers to be separated from the cis isomers. The combination of the GLC analyses of FAME and DMOX derivatives gave results comparable with those obtained by GLC of FAME after preceding Ag‐TLC, while saving about 100 h of manpower per 25 samples. It allowed the identification and quantitation of 11 trans and 8 cis isomers and resulted in 25% higher values for total C 18:1 trans , compared with the analysis of FAME alone. The combination of DMOX and FAME analyses, as applied to the analysis of 14 foods that contained ruminant fat and partially hydrogenated vegetable and fish oils, indicated that the most common isomers were 11 t in ruminant fats, 9 t in partially hydrogenated fish fats, and either 9 t or 10 t in partially hydrogenated vegetable fats. The combination of GLC analyses of FAME and DMOX derivatives of fatty acids improves the quantitation of 18‐carbon fatty acid isomers and may replace the laborious and time‐consuming Ag‐TLC.