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United States Department of Agriculture

Agricultural Research Service

Title: Simplifying Fatty Acid Analyses Using a Standard Set of Glc Conditions. II.ECL Values for Cis and Trans-Isomers of Monoethylenic C18 Fatty Acid Methyl Esters for the Liquid Phase Carbowax-20m

item Thompson Jr, Raymond

Submitted to: Journal of Chromatographic Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 11, 1996
Publication Date: N/A

Interpretive Summary: Information on the levels of trans- and cis-fatty acids is of high interest to scientists engaged in preparing and maintaining our food compositional databases. However, methodological advances, leading to greater reliability and cost-effectiveness, must occur before these demands can be satisfied. Advances are needed for the analysis of these components in margarines, other foods containing partially-hydrogenated fats and oils, in multicomponent items such as recipes, entrees, (composited) total-daily-diets, and in biological tissues and fluids. This report describes the gas-liquid chromatography separation characteristics of all of the principle trans- and cis-fatty acid isomers on Carbowax-20M capillary columns, the standard column for general fatty acid analyses. The retention times of the isomeric fatty acid methyl esters are reported in the equivalent chain length system, the most convenient, standardized way of expression of characteristics in the gas-liquid chromatography of fatty acid methyl esters. The influence of column temperature on equivalent chain length was also studied and reported; with this additional information one can project the location on complicated chromatography traces of each of the myriad isomers. Further benefits can accrue if equivalent chain length values are conveyed along with the analysts' quantative report to database specialists.

Technical Abstract: The Carbowax-20M liquid phase is becoming the standard in gas chromatography for general fatty acid analyses because it simplifies the work, and it reduces the chance for errors in identification of the fatty acids. Isothermal analysis using the Carbowax-20M column, as opposed to temperature programming, provides further simplifications and ruggedness to the analysis. A extensive compilation of characteristic separation factors for 59 different fatty acids has recently been reported, but it included information on only four of the approximately 20-24 isomeric C18 monoethylenic acids that occur in foods. This contribution serves to fill that void by providing the separation factors, in terms of equivalent chain lengths, for 25 additional trans- and cis-monoethylenic fatty acid methyl esters.

Last Modified: 4/22/2015
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