Comparison with solvent extraction

Comparison with solvent extraction. Although a substantial effort has been devoted to the development of satisfactory continuous counter-current ion-exchange processes for metal extraction, it is debatable whether any of... 

Extraction isotherms of nitric, sulphuric, and hydrochloric acids in comparison with solvent extraction data (Figure 8.15) show that extraction capacity of TBP in TVEX resins. An increase of TBP capacity in TVEX-TBP is caused by the extractant state in the polymer matrix. The extraction capacity of mineral acids by TVEX-TBP decreases in the sequence HNO3 > H2SO4 > HCI (Figure 8.15a,b,c), and when compared with TBP solvent extraction performance, the capacity of the impregnated polymers exceeds 1.5 times the capacity of HNO3, 3.5 times that of HCI, and several times that of H2SO4. 

Validation of true extraction efficiency normally requires the identification and quantitation of field-applied radiolabeled analyte(s), including resulting metabolites and all other degradation products. The manufacturer of a new pesticide has to perform such experiments and is able to determine the extraction efficiency of aged residues. Without any identification of residue components the calculation of the ratio between extracted radioactivity and total radioactivity inside the sample before extraction gives a first impression of the extraction efficiency of solvents. At best, this ratio is nearly 1 (i.e., a traceability of about 100%) and no further information is required. Such an efficient extraction solvent may serve as a reference solvent for any comparison with other extraction procedures. 

From plots of the distribution ratio against the variables of the system— [M], pH, [HA] , [B], etc.—an indication of the species involved in the solvent extraction process can be obtained from a comparison with the extraction curves presented in this chapter see Fig. 4.3. Sometimes this may not be sufficient, and some additional methods are required for identifying the species in solvent extraction. These and a summary of various methods for calculating equilibrium constants from the experimental data, using graphical as well as numerical techniques is discussed in the following sections. Calculation of equilibrium constants from solvent extraction is described in several monographs [60-64]. 

Flotron, V., J. Houesson, A. Bosio, C. Delteil, A. Bermond, and V. Camel. 2003. Rapid determination of polycyclic aromatic hydrocarbons in sewage sludges using microwave-assisted solvent extraction. Comparison with other extraction methods. J. Chromatogr. A 999 175-184. 

Ultrasound-assisted extraction (USE) is an effective method for leaching many analytes from different kinds of samples [52-55]. It is simple, fast, efficient, and inexpensive in comparison with conventional extraction techniques such as solvent extraction in the Soxhlet apparatus. Ultrasound-assisted solid-liquid extraction is an effective and time-saving extraction method. Sonication accelerates the mass-transfer process between two phases. Use of ultrasound results in a reduction in operating temperature, allowing the extraction of temperature-sensitive components. The ultrasound apparatus is cheaper and its operation is easier in comparison with other novel extraction techniques such as MAE. 

Supercritical fluid extraction (SFE), usually with carbon dioxide and, often, with a modifier, has become of increasing interest in the last few years because of its selectivity, preconcentration effect, efficiency, simplicity, rapidity, cleanness, and safety, mainly concerning the extraction of organic compounds prior to separation and detection by chromatographic techniques. It has several advantages over classical solvent extractions, in comparison with recent extraction techniques. Approaches to obtain quantitative extractions, including fluid choice, extraction flow rate, modifiers, pressure, and temperature, are presented, as well as the potential for SFE to extract polynuclear aromatic hydrocarbons (PAHs) from soils, sediments, and biota. Improvements and new environmental applications are also reported. 

The standard chemical and biological methods of analysis are those accepted by the JnitedStates Pharmacopeia XXIII as well as the ones accepted by the AO AC in 1995 (81—84). The USP method involves saponification of the sample (dry concentrate, premix, powder, capsule, tablet, or aqueous suspension) with aqueous alcohoHc KOH solvent extraction solvent removal chromatographic separation of vitamin D from extraneous ingredients and colormetric deterrnination with antimony trichloride and comparison with a solution of USP cholecalciferol reference standard. 

Optimization. Optimi2ation of the design variables is an important yet often neglected step in the design of extractive distillation sequences. The cost of the solvent recovery (qv) step affects the optimi2ation and thus must also be included. Optimi2ation not only yields the most efficient extractive distillation design, it is also a prerequisite for vaUd comparisons with other separation sequences and methods. 

After extraction of the neutral oil from the AOS sample, the neutral oil is made up volumetrically to at least a 10% solution in hexane. Of this solution 4 pi is spotted onto a silica gel TLC plate, together with terminal 5-sultone standard in the range 0.4-4 pg (equivalent to 0.1-1% sultone in the neutral oil). It is twice developed in a chamber saturated with 2-propyl ether. The solvent is completely evaporated and the spots visualized by vapor phase sulfuric acid charring using the technique described by Martin and Allen [139]. Humidity is not critical (10-30% is optimum) and activation of the plates has not been found necessary, but it might be required under conditions of high humidity. The level of sultone can be estimated by visual comparison with the standards or by the use of a densitomer. 

Using a simple solvent extraction procedure to minimize matrix effects, a diclofop-methyl immunoassay was developed for milk, a number of edible plant products, and other matrices. Gas chromatography (GC) and liquid scintillation counting (LSC) of a C-labeled analyte were used as reference methods to compare with enzyme immunoassay (EIA) results. The methods were well correlated, with comparison of EIA... 

Figure 2.4 Comparison of a typical separation on a packed and a open tubular column. The seunple (solvent extract of river water) is the same in both cases. (Reproduced with permission from ref. 135. Copyright Ann Arbor Science Publishers).

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