Separation of the Fatty Acids in Menhaden Oil as Methyl Esters with a Highly Polar Ionic Liquid Gas Chromatographic Column and Identification by Time of Flight Mass spectrometry

Abstract

The fatty acids contained in marine oils or products are traditionally analyzed by gas chromatography using capillary columns coated with polyethylene glycol phases. Recent reports indicate that 100 % cyanopropyl siloxane phases should also be used when the analyzed samples contain trans fatty acids. We investigated the separation of the fatty acid methyl esters prepared from menhaden oil using the more polar SLB-IL111 (200 m × 0.25 mm) ionic liquid capillary column and the chromatographic conditions previously optimized for the separation of the complex mixture of fatty acid methyl esters prepared from milk fat. Identifications of fatty acids were achieved by applying Ag(+)-HPLC fractionation and GC-TOF/MS analysis in CI(+) mode with isobutane as the ionization reagent. Calculation of equivalent chain lengths confirmed the assignment of double bond positions. This methodology allowed the identification of 125 fatty acids in menhaden oil, including isoprenoid and furanoid fatty acids, and the novel 7-methyl-6-hexadecenoic and 7-methyl-6-octadecenoic fatty acids. The chromatographic conditions applied in this study showed the potential of separating in a single 90-min analysis, among others, the short chain and trans fatty acids contained in dairy products, and the polyunsaturated fatty acids contained in marine products.

Silver ion solid‐phase extraction cartridges employing glass housings overcome the limitations observed in the GC analysis of animal lipids with low trans fatty acid content

“…It was evident from the results of the new glass cartridge that the TFA isomers of 16:1 (9t-, trace amounts 10t-, 11t-/12t-, 13t-, and 14t-16:1), and 18:1 (9t-, trace amounts 10t-, 11t-, 12t-, and trace amounts of 15t-18:1) could now be identified. In addition, these results agreed with the identification of these FAME resolved and identified using the ionic liquid GC column SLB-IL111 [7,11]. This identification was not possible using the commercial Ag þ -SPE cartridges because of the many additional peaks (labeled as X) in the trans fraction, and impurities that co-eluted with some of the trans-MUFA isomers, specifically in the trans-16:1 region (Fig.…”

Application of Silver Ion High‐Performance Liquid Chromatography for Quantitative Analysis of Selected n‐3 and n‐6 PUFA in Oil Supplements

“…The observed elution order of positional 18:3 ALA and GLA isomers in Ag-HPLC differs from that obtained with GC [27], where the GLA isomer elutes before ALA. In this instance, the GLA isomer is retained most strongly on the stationary phase, since the distance between the two interaction sites in FA molecule (the double bond and the oxygen functionality) is shifted by three carbon atoms in contrast to the ALA isomer.…”

Regioisomeric and enantiomeric analysis of triacylglycerols

“…This work is one of the most complex studies identifying regioisomers of TAG in fish oil. As the authors point out, the number of actually present TAG is much higher, as more than 100 FA were found in menhaden oil by GC-MS [28], which would, in accordance with Table 1, point to the presence of some half a million TAG excluding enantiomers [27].…”