Separation of racemic 2-alkyl-branched fatty acid methyl esters by gas chromatography on a commercially available chiral phase (original) (raw)
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Journal of Chromatography A - J CHROMATOGR A, 1987
Of the several facets of technique that must be addressed to allow the generation of highly accurate results by gas chromatographic analysis of fatty acid methyl esters, that of split injection to capillary columns has long been a major problem. A practical solution of this problem is now proposed. Three factors were found to be of major importance in achieving highly accurate results viz. avoidance of needle discrimination when injecting, very rapid vaporisation of the sample and complete homogenisation of the sample with the carrier gas stream. High speed of injection was found to be a highly effective means of avoiding needle discrimination. Rapid vaporisation of the sample was achieved by the use of relatively dilute solutions of analyte in the solvent, the smallest sample size commensurate with obtaining a chromatogram that could be accurately quantitated and, particularly, by the use of injector temperatures considerably higher than those generally adopted. Good mixing of the vaporized sample with the carrier gas was achieved with a number of injector insert designs, but, with improvement of design, it was found possible to achieve linear splitting over a wide range of operating conditions. The most controversial recommendation is to use very high injection temperatures, but it has been shown that the commonly held view that this may cause pyrolysis of fatty acid methyl esters is not true, even when the esters are highly unsaturated. * For Part V, see ref. 13.
Evaluation of New Stationary Phases for the Separation of Fatty Acid Methyl Esters
Chromatographia, 2006
In the analysis of fatty acids, one of the most commonly used tools is a GC separation of the fatty acid methyl esters (FAME). Many researchers perform this separation using a non-polar phase such the ubiquitous 5% phenyl / 95% methyl capillary columns found in most every chromatography laboratory. Numerous laboratories have also turned recently to polar phases such as 70% cyanopropyl columns, as this type of chemistry provides increased selectivity for unsaturated compounds, and thus improved separation of cis/trans and x 3 /x 6 FAME isomers. Here, a series of columns nominally having 60, 70, 80, and 90% bis-cyanopropyl content have been tested for the separation of FAME isomers. Trends in retention and the influence of increasing phase polarity on effective and fractional chain lengths are highlighted to provide the FAME chromatographer with insight into which of these novel stationary phases might be best suited to their particular application. In addition, the elution temperatures (T e) of the FAME and linear alkane standards are presented, as this information will be of value to comprehensive twodimensional multidimensional GC (GC • GC) users who wish to use these columns in the primary dimension separation.
Journal of Chromatography A, 1990
Enantiomers of monohydroxy polyenoic fatty acids containing a conjugated diene system can be separated on an (R)-(-)-N-(3,5-dinitrobenzoyl)-cc-phenylglycine (DNBPG) column. For all hydroxy fatly acids tested the s-isomer is earlier eluted than the R-isomer. Columns with ionically linked chiral phases show a better enantiomer resolution than those with covalently linked phases. Derivdtization of the hydroxy polyenoic fatty acids to their corresponding benzoyl or naphthoyl derivatives strongly improved the enantiomer resolution, but reversed the elution order. Various Pirkle-type chiral stationary phases and several derivatization procedures were tested to optimize the enantiomer resolution. The best resolutions were achieved for the separation of the naphthoyl esters on a DNBPG column. There are considerable differences in the enantiomer resolution between columns obtained from different manufacturers. Some racemic diastereomers of dihydroxy polyenoic fatty acids which cannot be separated by reversed-and normal-phase high-performance liquid chromatography were separated on (R)-DNBPG columns,
Journal of chromatography. B, Biomedical applications, 1996
We have developed a two-step method to purify fatty acid ethyl esters (FAEE) using solid-phase extraction (SPE), with a recovery of 70 +/- 3% (mean +/- S.E.M.) as assessed using ethyl oleate as a recovery marker from a standard lipid mixture in hexane. The first step of the SPE procedure involves application of a lipid mixture to an aminopropyl-silica column with simultaneous elution of FAEE and cholesteryl esters from the column with hexane. Gas chromatographic analysis of FAEE without interference from cholesteryl esters may be performed using the eluate from the aminopropyl-silica column, thus eliminating the need for an octadecylsilyl (ODS) column in this case. The FAEE can then be separated from the cholesteryl esters, if necessary, by chromatography on an ODS column and elution with isopropanol-water (5:1, v/v). Both the aminopropyl-silica and ODS columns were found to be effective for up to four uses. To permit isolation of specific FAEE species following isolation of total F...
Column Selection for the Analysis of Fatty Acid Methyl Esters Application
The analysis of fatty acid methyl esters (FAMEs), derived from food, is a very important food characterization procedure. These esters are normally analyzed on columns coated with polar stationary phases, such as polyethylene glycols or cyanopropyl silicones, allowing separation of fatty acids according to their carbon number, the degree of unsaturation, the cis-trans configuration, and the location of the double bonds.
Lipids, 1999
Operating irom one to six silver ion-high-periormance liquid chromatography (Ag·-HPLO columns in series progressively improved the resolution of the methvl esters of conjugated linoleic acid (CLA) isomeric mixtures ir~m natural and commercial products. In natural products. the 8 trans. 10 cis-octadecadienoic (18:2) acid was resolved irom the more abundant 7 trans. 9 cis-18:2. and the 10 trans. 12 cis-18:2 was separated irom the major 9 cis. 11 trans-18:2 peak. In addition, both 11 trans. 13 cis-18:2 and 11 cis, 13 trans-18:2 isomers were iound in natural products and were separated: the presence oi the latter. 11 cis, 13 trans-18:2, was established in commercial CLA preparations. Three Ag+-HPLC columns in series appeared to be the best compromise to obtain satisiactorv resolution oi most CLA isomers iound in natural products. A smgle Ag+-HPLC column in series with one oi several normal-phase columns did not improve the resolution oi CLA isomers as compared to that of the iormer alone. The 20:2 conjugated iatty acid isomers 11 cis. 13 trans-20:2 and 12 trans. 14 cis-20:2. which were svnthesized by alkali isomerization irom 11 CIS. 14 ClS-20:2. eluted in the same region oi the Ag·-HPLC chromatogram lust beiore the corresponding geometric CLA isomers. Therefore, CLA Isomers will require Isolation based on cham length prior to Ag--HPLC separation. The positions of conjugated double bonds in 20:2 and 18:2 isomers were established hy gas chromatographY-electron ionization mass spectrometry as their 4.4-dimethvloxazoline derivatives. The double-hand geometry was determined by gas chromatographv-dlrect deposltlon-Fourier transiorm mfrared spectroscopy and hv the Ag' -HPLC relative elution order.
Journal of Chromatography A, 2003
Comprehensive gas chromatography (GC×GC) is an adequate methodology for the separation and identification of very complex samples. It is based on the coupling of two capillary columns that each give a different but substantial contribution to the unprecedented resolving power of this technique. The 2D space chromatograms that derive from GC×GC analysis have great potential for identification. This is due to the fact that the contour plot positions, pinpointed by two retention time coordinates, give characteristic patterns for specific families of compounds that can be mathematically translated. This investigation concerned the application of this principle to fatty acid methyl esters that were grouped on an equal double bond number basis. The ester samples were derived from various lipids and all underwent bidimensional analysis on two sets of columns. Peak attribution was supported by mass spectra, linear retention indices and information reported in the literature.