Diethyl ether fractional polarity

Silica gel thin-layer plates may be used to separate lipids on either a preparative or an analytical scale. They are sometimes used to fractionate the lipids into classes prior to removal from the plate and further analysis by GLC. In this case the appropriate area of silica gel is scraped off and the lipid extracted into chloroform or diethyl ether containing 1-2% methanol for simple lipids or into chloroform-methanol-water (5 5 1) for polar lipids. 

Other factors important to the choice of catalyst are its stability under the reaction conditions (see Section 1.1) and its removal from the organic phase at the end of the reaction. Ideally, the catalyst should be sufficiently hydrophilic to be washed from the product by water, but any catalyst having this property has, by implication, a lower lipophilicity and lower catalytic effect. Where the product is volatile, it can be separated from the catalyst and isolated by fractional distillation of the organic phase or, alternatively, the catalyst can be precipitated from the concentrated organic phase by the addition of a non-polar solvent, such as diethyl ether, and removed by filtration. On a small scale, the catalyst can be separated efficiently by direct chromatography of the organic phase from, for example, silica. This procedure is, however,... 

The ether extract containing the catalyst and neutral products was fractionally distilled (130°-160°C at 0.01 mm Hg). The soluble catalyst was concentrated in the pot residues. The distillation fractions were then chromatographed through a silicic acid column. Monoesters and cyclic ketones were eluted successively with 5 95 and 10 90 diethyl ether petroleum ether, and more polar material was eluted with 15 85 diethyl ether. -petroleum ether followed by pure diethyl ether. 

The weak adsorption of phylloquinone on silica gel (Table 5) provides the basis for silica purification of lipid extracts of milk and infant formulas in vitamin K assays. Haroon et al. (98) washed the hydrocarbons from a silica gel column with petroleum ether, after which the phylloquinone fraction was eluted with petroleum ether containing 3% diethyl ether lipids that were more polar than phylloquinone were retained on the column. 

Silica columns can tolerate relatively heavy loads of triglyceride and other nonpolar material. Such material is not strongly adsorbed and can easily be washed from the column with 25% diethyl ether in hexane after a series of analyses (83). Procedures for determining vitamins A and E have been devised in which the total lipid fraction of the food sample is extracted with a non-aqueous solvent, and any polar material that might be present is removed. An aliquot of the nonpolar lipid extract containing these vitamins is then injected into the liquid chromatograph without further purification. Direct injection of the lipid extract is possible because the lipoidal material is dissolved in a nonpolar solvent that is compatible with the predominantly nonpolar mobile phase. Procedures based on this technique are rapid and simple, because there is no need to saponify the sample. 

Methanol appears to be the most suitable relatively inert solvent for the extraction of dried plant material either in the cold or at higher tent eratu-re. After evaporation of the solvent, the residue is extracted with dilute add (e.g. 1 to 5% HCl or H2SO4) and filtered. The insoluble material is the best source of non-basic alkaloids (dihydro-, 0x0-, and norderivatives of QBA) [61,65]. The acidic filtrate is made alkaline with NaaCOs or NH3 and extracted repeatedly with a non-polar solvent. The most advantageous choice seems to be diethyl ether because its high selectivity yields a crude alkaloid fraction of relatively good purity (up to 95%). Other solvents, especially chloroform, dissolve much more of the tar material so that the crude fi action may contain up to 90% of non-alkaloidal matter. 

The most widely applied procedure is indirect quantification by extracting the fractions from the adsorbent layer in the presence of an internal standard, transmethylating, and subjecting the methyl esters of the fatty acids to gas chromatography (GC) analysis. Information is simultaneously obtained on the composition of the fractions and their absolute amounts. In practice, the sample is resolved on a preparative plate, each distinct zone is carefully scraped off, a standard solution of the internal standard (usually an odd-chain fatty acid methyl ester) is added, and the material is extracted with a suitable polar solvent such as diethyl ether or a chloroform-methanol mixture. More complicated extraction procedures are sometimes needed for polar complex lipids. Fatty acid methyl esters... 

Organic solvents have long been used for extraction and sequential extraction, which is fractionation of a sort (Flaig et al., 1975 Schnitzer, 1978). While the direct use of organic solvents in fractionation has not been widespread, nonetheless, the technique has received some attention. For instance, the separation of hymatomelanic acid from precipitated humic acid is obtained by extraction with ethanol (Oden, 1919). Ethanol has been used to bring about fractional precipitation by addition to alkaline solutions of humic acid (Kyuma, 1964 Kumada and Kawamura, 1968). There is no reason why other water-miscible solvents such as acetone and methanol should not be used in this way. Solvents that are highly immiscible with water (e.g., hexane and benzene) do not appear to remove any substantial fraction of humic substances. These are perhaps best used to remove nonhumic substances (such as fats and waxes) prior to extraction. However, recent work by Allen and MacCarthy (personal communication) has shown that more polar water-immiscible solvents, such as methyl isobutyl ketone and diethyl ether, can be used successfully to purify and fractionate humic substances. 

Liquid chromatography (Hostettman et al., 1986) in its many forms is a separation technique based on the polarity of the analytes and their partition between the mobile and stationary phases, and is therefore complementary to fractional distillation, which separates materials by their boiling point. The usual sequence for fractionating an essential oil or extract is to distil it first and then apply liquid chromatography to the distillation fractions as a further fractionation procedure, rather than as an analytical tool. The selectivity of the technique is achieved by choosing a stationary phase, usually from the various activities of silica gel, and varying the polarity of the mobile phase, the solvent, by mixing a non-polar component (such as hexane or pentane) with different amounts of a more polar component (such as diethyl ether, ethyl acetate or chloroform). 

The ligand concentration affects the fraction of ferric ions that is in the form of the neutral complex Fe(SCN)3 on that basis one might want to use a thiocyanate concentration of about 2.5 M (pL= log[SCN] — 0.4), where [(Fe(SCN)3] goes through a maximum in Fig. 5.1-2. Indeed, Fe(III) can be extracted into oxygen-containing non-polar solvents such as diethyl ether or isobutyl alcohol, and can then be determined spectrometrically in that solvent. 

In an attempt to simplify the complex mixture of chemicals present in extracts of labrusca grapes we have used 6% water deactivated Florisil developed with solvents of increasing polarity (ii). Made hy mixing diethyl ether at 0, 1, 3, 10, 30, and 100% with pentane, each solvent has approximately twice the polarity of the previous one (Ifi.). With Concord grape juice extracts the fraction with the most labrusca like odor character was the 3% fraction which had a very strong sweet floral characteristic. An analysis of this fraction (li) showed the presence of damascenone [l-(2,6,6-trimethyl-l,3-cyclohexadien-l-yl)-2-buten-l-one] a compound previously reported to be present in vinifera eranesf17) as well as other natural productsQfi.). 

Two procedures (Fig 1) for tannin extraction from the bark were used alkaline extraction with a solution of NaOH, 1 % (w/w) fractionated extraction using a sequence of solvents with increasing polarity and decreasing specificity for tannins ethanol and hot water, which were utilised after a diethyl ether pre-treatment to remove the lipophilic components. 

General instructions for TLC are given in Kates (1972) and Christie (1982). Useful solvent systems for use with silica gel G plates are listed by Jensen and Pitas (1976). For assay of polar contaminants, the acylglycerols should be separated with petroleum ether (35 5 °C fraction)-diethyl ether-acetic acid... 

For monitoring the hydrolysis, 1— 5 jd of the reaction mixture is applied to silica gel G layers on narrow plates and developed with petrol ether (60—70° C)-diethyl ether-acetic acid (70 + 30 + 2). The lipid fractions are visualised by spraying the chromatogram with the chromic acid-sulphuric acid reagent (No. 46) and heating. At the beginning of saponification, spots of substances of low polarity are visible ahead of the fatty acid spot. After complete hydrolysis, only the spots of the acids, of the non-polar compounds (hydrocarbons) ahead of them and of the strongly polar compoimds (mono- and polyalcohols) behind them are visible. 

Fats, oils, waxes and other neutral lipids have been fractionated into compound classes mostly by adsorption TLC on sihca gel G. Petrol ether-diethyl ether mixtures have been the solvents generally employed. Alcohohc and aqueous solvents are needed for separating strongly polar lipids on silica gel G layers the fractionation of such materials into compound classes is consequently often effected by partition rather than by adsorption. Reversed phase partition chromatography on hydrophobic layers has been used in some cases for fractionating lipids into compound classes. 

Solvents. The choice of solvent is governed by the polarity of the components of the lipid mixture and the separation desired. Table 67 contains a list of solvents for fractionation of neutral lipids through TLC. Petroleum ether containing 1—5 % benzene or diethyl ether is particularly good for separating hydrocarbons, alkyl esters, steryl esters and polyenol esters into compound classes [52, 118]. Compounds with one or several... 

Petroleum ether containing 10—50% diethyl ether has been used for fractionating alcohols and aldehydes, mono-, di- and triglycerides [114, 135, 165, 183]. Weakly polar lipids migrate near the front in this solvent mixture and are scarcely separated from one another. The above-mentioned solvents, plus 1—2% acetic acid, are best for TLC of lipid mixtures containing free fatty acids this addition prevents streak and tail formation [114, 118]. 

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