Thin-layer chromatography saturated/unsaturated

Argentation thin-layer chromatography is an extemely useful procedure for the separation of methyl esters of fatty acids. Saturated fatty acids have the highest Rf values, which decrease with the increasing degree of unsaturation, and for a particular acid, the trans isomer usually travels ahead of its corresponding cis isomer. The solvents most commonly used contain hexane and diethyl ether (9 1) although a mixture of 4 6 is used to separate compounds with more than two double bonds. In order to separate positional isomers of the same acid, conditions must be carefully controlled and multiple development in toluene at low temperatures is often necessary. 

Extraction and extract separation. The freeze dried samples were ground and extracted with chloroform for one hour at 55°C. Free sulfur was removed by percolating the extracts over an activated copper column. Resulting extracts were separated using thin layer chromatography (Merck precoated T.L.C. Silica-gel 60f-254) with cyclohexane as the eluting solvent. Three fractions were obtained an immobile polar fraction, an "intermediate fraction, and a saturated/unsaturated hydrocarbon fraction. 

Gunstone ct found that separation of saturated and unsaturated fatty acid glycerides by crystallization at -10° is improved by addition of silver nitrate in methanol to complex with the unsaturated components. Morris reports separation of CIS and trans fatty acids and oxygenated fatty acids by thin-layer chromatography on silica gel impregnated with silver nitrate. With untreated silica there was no separation. 

Some results for the effects of addition of different lipid compounds on loaf volume of a base flour are shown in Figure 7.10 (Sroan 2007). The natural lipid from flour has been separated into two fractions polar and nonpolar. Thin layer chromatography (TLC) of the fractions is shown in Figure 7.11. Polar lipids comprise mainly galactolipids and phospholipids. Their addition enhances loaf volume. In contrast, the nonpolar fraction, which comprises mono-, di-, and triglycerides and free fatty acids as the main components, causes depression of the loaf volume. The unsaturated linoleic acid, which is the major fatty acid in wheat, also depresses loaf volume, whereas the saturated palmitic acid has no effect. Another saturated fatty acid, myristic acid, affected loaf volume negatively. 

Child, P., Kuksis, A., and Myher, J. J. Resolution of Saturated and Unsaturated 53-Cholanoic Acids by Gas-Liquid and Thin-Layer Chromatography... 

Dongowski. G. (1997). Determination of saturated and unsaturated oligogalacuronic acids by means of thin layer chromatography. J. Chromatogr., A 756 211-217. 

Touchstone, J. C., Levin, S. S., Dobbins, M. F., Carter, P.J. (1981). Differentiation of saturated and unsaturated phosphohpid on thin layer chromograms. Journal of High Resolution Chromatography Chromatography Communications 4 423-424. 

Isolation of the hydrocarbons from other lipids The total lipid extract may be subjected to removal of elemental sulphur by passage through an activated copper column (Blumer, 1957) and then to chromatographic separation on adsorbent columns or thin layer plates. For column chromatography, silic el is used with a short alumina bed on the top of the silic el. Both adsorbents should be partially deactivated by the addition of water (2—5%) to prevent the formation of artifacts (Blumer, 1970). Elution with a non-polar solvent such as hexane or pentane and subsequently with mixtures of non-polar and polar solvents, e.g. benzene and methanol, permits the isolation of several fractions containing saturated, unsaturated, aromatic hydrocarbons and more polar compounds (methyl esters, alcohols, acids, phenols and heterocyclic compounds). The interference from esters encountered in the isolation of aromatic hydrocarbons can be avoided prior to separation by saponification of the esters of fatty acids, which are easily removed. 

Other separating techniques may be used to separate total hydrocarbons into different classes. Thus, the normal paraffins are selectively removed by 5 A molecular sieve (Mortimer and Luke, 1967) or by urea adduction, although it is less specific than the former method. Unsaturated hydrocarbons are separated from the saturated fraction by thin layer or column chromatography on silicic acid/AgNOj. 

Saturated lecithins and the three types of aldehydic cores obtained by reductive ozonolysis of unsaturated lecithins can be separated through reversed phase partition chromatography [168]. Fig. 147 shows photo-densitometric curves from thin-layer chromatograms of fission products derived from the lecithins of egg, bovine spinal cord, soya bean and wheat germ. 

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