Solvent extraction efficiency

On the other hand, single-residue methods developed by the applicants give basic information about appropriate cleanup steps and specific determination procedures. In addition, not many laboratories other than those from the applicants are able to test the real solvent extraction efficiency. The reason is that extraction studies need radio-labeled incurred residues instead of fortified samples. Hence enforcement methods provided by the manufacturers accelerate the development of methods which meet the needs of (official) food control laboratories. 

Solvent Extraction Aqueous sample is partitioned with an immiscible organic solvent. Extraction efficiency depends on the affinity of the solute for the organic solvent. All sample types Samples with a high affinity for water are not extracted. Extractions can be performed by a simple single equilibration or by multiple equilibrations with fresh solvent. Solvent impurities concentrated along with sample. 

As the process of the gas sampling and the solvent extraction has to be carried out quickly (within 3 min at the longest) for the direct measurement of the Rn-220 decay, accurate measurements of the gas volume and the temperature are not possible. Therefore, the coexisting Rn-222 is used as a tracer for the determination of the gas volume and the solvent extraction efficiency that is, another gas... 

FIGURE 3 2 Solvent extraction efficiencies (EF) as functions of dielectric constants (D), solubility parameters (6), and polarity parameters (P and E -). Solvents studied silicon tetrachloride, carbon disulfide, n pentane. Freon 113, cyclopentane, n-hexane, carbon tetradiloride, diethylether, cyclohexane, isooctane, benzene (reference, EF 100), toluene, trichloroethylene, diethylamine, chloroform, triethylamine, methylene, chloride, tetra-hydrofuran, l,4 dioxane, pyridine, 2 propanol, acetone, ethanol, methanol, dimethyl sulfoxide, and water. Reprinted with permission from Grosjean. ... 

The distribution ratios (D s) for crown-ether-based extraction processes using conventional solvents depend on two major factors (1) the thermodynamic driving force for cafion complexation by a crown efher and (2) the solvation of fhe cafion and counfer anion by the organic solvent [1,4] the former factor is usually thermodynamically favored (see Equation 10.3). Difficulties in increasing the solvent-extraction efficiency of conventional solvent-extraction systems using crown ethers as extractants lie in the... 

The so-called solvent extraction method by toluene, o-xylene or carbon disulfide is the most common and frequently used extraction method, in which metallofullerenes and hollow fullerenes are preferentially dissolved in solvents. The so-called Soxhlet extraction (a continuous and hot solvent extraction) or ultrasonic extraction is normally employed to increase the solvent extraction efficiency (Khemani et al., 1992). Insolubles in soot are easily separated from this solution by filtration. However, in many cases, the toluene or CS2 extraction is not sufficient, since nearly half of the metallofullerene still remains in the residual soot even after the extensive CS2 extraction. It has been found that metallofullerenes are further extracted from the residual soot by such solvents as pyridine (Inakuma et al., 1995) and 1,2,4-trichlorobenzene (Yamamoto et al., 1994a,b). The metallofullerenes were found to be concentrated in this pyridine or trichlorobenzene extracted fraction. When necessary, the metallofullerene extracts can be stored in carbon disulfide solution for an extended period of time, up to a year. 

The polymer content in polymer hybrids before (Pb) and after (Pa), solvent extraction efficiency E was calculated according to the equation E = 100(Pb-Pa)/Pb(100-Pa). 

Grinding, rolling, or flaking After dehulling, the meats are reduced in size, or flaked, to facilitate oil removal. Proper moisture content of flie seeds is essential for flaking, and if the moisture level is too low, the seeds are conditioned, with water or steam, to raise flie moisture to about 11%. For solvent extraction, flakes are commonly not less than 0.203-0.254 mm (0.008-0.010 inch), which can be solvent extracted efficiently with less than 1% residual oil. Thinner flakes tend to disintegrate during the solvent extraction process and reduce flie miscella percolation rate. 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... 

Mechanical Pressing. Historically, the first large commercial production of oils from seeds and nuts was carried out using labor-intensive hydraulic presses. These were gradually replaced by more efficient mechanical and screw presses. Solvent extraction was developed for extraction of seeds having low oil content. For seeds and nuts having higher oil content, a combination of a screw press followed by solvent extraction is a common commercial practice (prepress—solvent extraction). 

Polyethers are usually found in both the filtrate and the mycelial fraction, but in high yielding fermentations they are mosdy in the mycelium because of their low water-solubiUty (162). The high lipophilicity of both the free acid and the salt forms of the polyether antibiotics lends these compounds to efficient organic solvent extraction and chromatography (qv) on adsorbents such as siUca gel and alumina. Many of the production procedures utilize the separation of the mycelium followed by extraction using solvents such as methanol or acetone. A number of the polyethers can be readily crystallized, either as the free acid or as the sodium or potassium salt, after only minimal purification. 

Cementation. Cementation is the precipitation of copper from copper leach solutions by replacement with iron. It was formerly the most commonly used method of recovering copper from leach solutions but has been replaced by solvent extraction—electro winning. The type of iron used ia cementation is important, and the most widely used material is detinned, light-gauge, shredded scrap iron. This operation can be performed by the scrap iron cone (Keimecott Precipitation Cone) or a vibrating cementation mill that combines high copper precipitation efficiency and reduced iron consumption (41). 

Mass Transfer As mentioned earlier, spray columns rarely develop more than 1 theoretical stage due to the axial mixing in the column. Nevertheless, it is necesary to determine what column height will give this theoretical stage. It is recommended by Cavers in Lo et al. Handbook of Solvent Extraction p. 323 and p. 327, John Wiley Sons, New York, 1983 that the following equation be used to estimate the overall efficiency coefficient ... 

FIG. 15-47 Correlation of mixing-stage efficiency with power input and liquid flow rates. [Scheihel in Lo, Baird, Hanson, Handbook of Solvent Extraction, p. 428 John Wiley h- Sons, NY, 1983. Used with peimission.]... 

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