Technique of extraction with solvents

Occasionally emulsions are formed in the extraction of aqueous solution by organic solvents, thus rendering a clean separation impossible. Emulsion formation is particularly liable to occur when the aqueous 

Drawing a stream of air over the surface by inserting a tube, connected to a water pump, above the mixture. 

Saturating the aqueous phase with sodium chloride. 

Addition of a few drops of alcohol or other suitable solvent (this is generally undesirable). 

In general, however, satisfactory separation will be obtained if the mixture is allowed to stand for some time. 

The fire hazard is reduced also by employing di-iso-propyl ether (b.p. 67-5°), but this solvent is much more expensive than diethyl ether. 

The theory of extraction with solvents has been discussed in Section 

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Prepress Solvent Extraction. Solvent extraction is relatively costly and is not well suited for the high-oil content of cottonseed. Mechanical pressing leaves about 5% oil in the press-cake, and it is desirable to recover as much oil as possible. A logical processing step was to combine the two extraction techniques. With prepress solvent extraction, cottonseeds are pressed to remove most of the oil and then the oil remaining in the press-cake is extracted with solvent. This solvent extraction operates on a reduced volume of feed stock (i.e., press-cake, as opposed to full-fat flakes) and, therefore, requires a modest size extractor with modest amounts of desolventizer and solvent. 

With solid materials (such as foods) the initial step in sample preparation involves Soxhlet extraction. With this technique a solid sample is placed in a permeable thimble above a flask of solvent but below a cold water condenser (Figure 8.2). The extraction solvent is boiled, condenses and runs down into the part of the apparatus containing the sample. As the container fills, the sample is extracted with solvent. The apparatus is designed such that as the solvent level reaches a certain height it siphons back into the flask at the bottom along with any extracted residue. The process is then continuously repeated often for many hours. The end result is a... 

The use of different names for the technique can lead to confusion as it may leave the impression that the names refer to different techniques rather than a single one involving extraction with solvent at a high pressure and temperature. However, authors tend to use different names for the static and dynamic modes, even though the names provide no clue as to which mode was used. 

One of the most important analytical techniques used today is high-resolution gas chromatography (HRGC). The pesticide residues can be analyzed by specihe or multiresidue methods. When crops are treated with several pesticides, the use of a multiresidue method is preferable due the reduced cost and time of analysis. The methods of pesticides residue analysis usually present an initial step of extraction with a solvent which is not miscible with water, followed by a cleanup step and the analyte determination by gas chromatography. 

The coke content of the catalysts was measured by combustion-volumetry after the run. The differential thermal analysis (DTA) of the used catalysts was performed with an Aminco Thermoanalyzer using oxygen as dynamic gas. The soluble fraction of coke from used catalysts was extracted with solvents and the solutions were analyzed by several techniques in order to determine their nature. 

Chromatography on thin layers of silica gel or alumina is a standard technique for identifying and separating marijuana constituents. Marijuana is extracted with solvent as described above, and a small amount is spotted with a capillary tube or micropipette on one end of the plate. The plate is then placed vertically in a small amount of solvent. The solvent is drawn to the other end by capillary action, which carries the cannabinoids present in the... 

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