Differential extraction process

All filtering and extraction systems must be checked for compatibility with the analyte of interest. Some or all of the analytes may be absorbed or otherwise lost during the extraction process, and this must be known beforehand. Carbon may be lost by high vacuum differentials between sampler and soil water. Long extraction times may lead to distortions in the results of the sample analysis [5],... 

A single-stage extraction using the same total volume of solvent achieves only 92% extraction, and the extract concentration is only 0.23, vs. nearly 0.25 for the cross-flow extraction. The use of four cross-flow extraction stages is clearly preferable to a single extraction. Equally, of course, the use of more than four extraction stages, each with a proportionately smaller volume, would improve the performance. In the limit, one would seek a differential contacting process similar to the Soxhlet extractor employed for extraction from solid phases, but such a contactor has not found use in solvent extraction. 

The term chromatography now embraces a variety of processes that are based on the differential distribution of the components in a chemical mixture between two phases. The difference between extraction processes involving a single equilibrium of two bulk phases and chromatography is... 

In order to describe and optimize the reverse micellar extraction process, Dekker et al. [ 170] have proposed a mathematical model, which satisfactorily describes the time dependency of the concentration of active enzyme in all the phases, based on the flow, mass transfer, and first-order inactivation kinetics. For each phase, a differential equation is derived. For forward extraction ... 

Various processing techniques, other than fermentation, can be utilized to remove phytic acid and other dietary fiber materials that reduce mineral absorption (109). Processes would include differential extraction and filtration techniques such as ultrafiltration (125, 126, 127). 

Although the most useful extraction process is with countercurrent flow in a multistage battery, other modes have some application. Calculations may be performed analytically or graphically. On flowsketches like those of Example 14.1 and elsewhere, a single box represents an extraction stage that may be made up of an individual mixer and separator. The performance of differential contactors such as packed or spray towers is commonly described as the height equivalent to a theoretical stage (HETS) in ft or m. 

If prior information is not available, solvent selection should be based on some small-scale trials. A few millimetres of suspension or solution to be extracted are placed in a small test tube and shaken with an equal volume of diethyl ether, when dissolution of suspended material clearly indicates that the solvent would be satisfactory. If the solution to be extracted is homogeneous initially, then the ether solution is removed with a dropper pipette on to a watch glass, and the ether is allowed to evaporate to determine whether material has been extracted. A little experience soon enables the student to differentiate between organic liquids so extracted and traces of water simultaneously removed during the extraction process. If extraction with diethyl ether proves unsatisfactory the experiment is repeated with a fresh sample of reaction mixture... 

There are four primary reasons why the mechanical extraction process is still selectively used. First, the mechanical extraction process can be furnished in very small scale, as low as 10 tons per day. The capital cost for small mechanical extraction facilities is considerably less than small solvent extraction facilities. In remote locations, freight differential can compensate for higher operating costs and lower yields. Second, there is a niche, high-value market for natural oils that have not been in contact with solvents or chemicals, requiring the use of mechanical extraction. Third, mechanical extraction can create a high bypass protein meal for ruminant animals that sells at a price premium over solvent extracted meal. Finally, mechanical extraction is often considered more reliable than solvent extraction when processing difficult materials (copra and palm kernel) in hot, tropical climates. 

Today, most shellac is produced on a commercial scale using machine processes involving extraction from seed lac using steam heat or solvent extraction with hot ethanol. Shellac produced by the heat and solvent extraction processes cannot usually be differentiated by chemical tests. 

Tbe extraction of phenol has been used by Schlosser and Kossaczky11 and Halwachs et al.16 as a model for studying liquid-membrane transport. The former group compared the liquid-membrane method to a conventional liquid-liquid double extraction process. They concluded thet liquid membranes have disliact economic ndvsmages in cases where type I or type 2 facilitation methods can be used (e.g., phanel or metal ion extractions). However, where one must rely on simple differential permeation (bydrocarbon seperations) rhe ndvantage is less clear-cut. 

Considerable work has been done to differentiate between bound and free chlorides, using cold-water dissolution, alcohol dissolution, etc. The results of such chloride-extraction processes strongly depend on the level of powder fineness, time of dissolution, etc., and no sufficient reproducibihty has been obtained. For routine analysis only acid soluble [51] or Soxhlet procedures are recommended. Recently, a method was proposed for determining water-soluble chloride [52]. 

Conventional forensic DNA analysis involves DNA extraction and purification, quantification, and amplification, followed by separation of PCR products, detection, and data analysis. In sexual assault casework, differential extraction, a cell sorting process by which DNA is differentially extracted from sperm and vaginal epithelial cells (or other nonsperm cell types), must be utilized to obtain enriched fractions of male and female DNA. In this chapter, we will discuss the specific development of these techniques on the microscale for application to forensic human DNA analysis. 

Eq. (6-24) may be also applied to differential stagewise extraction operated as a stagewise cross-flow extraction process, with the number of extraction cycles tending to infinity (n oo). The extract phase may be withdrawn continuously and fresh solvent is fed. For TV, - oo. 

Application of Eqs. (6-34)-(6-36) implies the state points of the fictitious mixtures D must lie on an extension of the connecting line between the state points F and E or R and or R and E, respectively. All three fictitious differential flow rates D have a common state point which is named the pol P, and is the intersection of the extended lines FEt and Ro,L , if the state points F of the feed mixture F, Ej of the extract phase E, R of the raffinate phase and L of the solvent phase are given. P gives the fictitious composition of the two phase system for fixed flow rates of R and E, and remains in the same place during the extraction process. The pol location is fixed by the feed/solvent ratio... 

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