title: Two methods for the separation of monounsaturated octadecenoic acid isomers.
abstract: The identification and quantification of complex mixtures of cis and trans octadecenoic (18:1) fatty acid isomers presents a major challenge for conventional one-dimensional GC/FID analysis of their methyl esters. We have compared the use of two methods to achieve optimized separations of positional and geometrical octadecenoic fatty acid isomers-comprehensive two-dimensional gas chromatography (GCxGC), and silver ion high performance liquid chromatography interfaced to atmospheric pressure photoionization (APPI) mass spectrometry. Nine isomers of octadecenoic acid methyl ester were well separated on a single silver ion column with a mobile phase of 0.018% acetonitrile and 0.18% isopropanol in hexane. Reproducible retention times were obtained with relative standard deviations of around 1% over 5 injections. The extra selectivity and reproducibility afforded by APPI-MS, together with the wide separation of cis and trans isomers by silver ion chromatography, resulted in a promising method for measurement of octadecenoic acid FAME. The GCxGC separation was performed using various column combinations, and optimal separation was obtained by coupling an ionic liquid column (Supelco SLB-IL100 [1,9-di(3-vinyl-imidazolium) nonane bis(trifluoromethyl) sulfonyl imidate]) in the first dimension with a SGE BPX50 (50% phenyl polysilphenylene-siloxane) in the second dimension. These methods have been applied to the analysis of octadecenoic acid in milk and beef fat.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, 410 Agriculture/Forestry Centre, Edmonton, Alberta T6G 2P5, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Villegas
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: J M
authors.initials: JM
authors.lastname: Curtis
mesh_terms: D000818:Animals; D002417:Cattle; D002849:Chromatography, Gas / Q000379:methods*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005229:Fatty Acids, Monounsaturated / Q000032:analysis*; D013058:Mass Spectrometry / Q000379:methods*; D008460:Meat / Q000032:analysis; D008892:Milk / Q000737:chemistry; D009829:Oleic Acids / Q000032:analysis*
chemical_list: D005229:Fatty Acids, Monounsaturated; D009829:Oleic Acids