Efficiency in Extraction

MAXIMUM EFFICIENCY in EXTRACTION. One may determine the maximum possible efficiency of an extraction by considering the fraction of solute that remains in the original phase (raffinate) after equilibrations. (j R is the symbol for this fraction, thus 

When the value of k is near to 0.5 or when equal amounts of solute are present in each phase, we evidence the most sensitive changes in kc or v2/V. Also, the fractional amount of total solute, (J), in a given phase asymptotically approaches one or zero for large or small values, respectively of the capacity factor, k. What this says is that when k is large or small, little effect is noted for cj when a large change occurs in k. Under the above conditions it becomes very difficult to remove the last traces of a component from either phase. It is for this reason that more than five extractions accomplishes little in regard to quantitative separation. Thus, when (1 - f ) 0.01, we assume complete separation of solute from one phase to another phase. 

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Removal by Centrifugal Force. This method is more efficient in extracting the particulate matter from a liquid due to the fact that the forces devcT oped are many times greater than the force of gravity. 

The examination of alternative solvent extraction sequences in this experiment, Aliquot A versus E, showed the sequence from nonpolar to polar solvent to be more efficient in extracting mutagens from the sample (Table II). This result could explain the lower recoveries of mutagenic activity via the modified Hites procedure compared with the recoveries found with the milling procedure (Table I). The published Hites method (18, 19) was used in this study, that is, extraction with isopropyl alcohol followed by benzene. Therefore, the results from our experiment suggest that a nonpolar to polar solvent sequence gives better recoveries of mutagenic components from a sample. 

The excellent procedures for dehydration of N-alkyl- and N-arylformamides developed by Hertler and Corey4 and by Ugi and co-workerss are unsuccessful with low-molecular-weight isocyanides. This common failure is probably due to poor efficiency in extraction of these very polar substances from water. The present method also has been successfully employed for the preparation of smaller quantities of methyl (50%), ethyl (45%), 5-butyl (35%) and cyclobutyl (24%) isocyanides.6 The procedure is less laborious than that reported earlier for ethyl isocyanide.7... 

This is true even if it is capable of dissolving the solutes. Supercritical solvents such as N2O and CHC1F2 are more efficient in extracting polar compounds, but their routine use is uncommon due to environmental concerns. The extraction efficiency of polar compounds by C02 can be improved by the addition of small quantities (1 to 10%) of polar organic solvents, referred to as modifiers. This is a common practice in SFE. Table 3.4 lists some common modifiers for supercritical CO 2. 

A similarly poor efficiency in extraction can also be seen in Fig. 11, where the extraction result for the product obtained by the radiation grafting of styrene onto polyethylene terephthalate)(PET) fibers13 is shown. In this case the unreacted PET can be extracted after most of PS homopolymer has been extracted by repeated solution-precipitation of the sample. It should be mentioned here that the solution procedure is also necessary to extract the unreacted PET. Such a solution-precipitation procedure is also necessary for nylon-styrene13 and poly(vinyl chloride)-acrylo-nitrile14 graft products so as to remove the homopolymers to a sufficient extent. 

The largest proportion of the total Fe was removed by ammonium oxalate, which attacks the amorphic fraction of iron oxide in the sediments (23). Among the low pH extractants, hydroxylamine was the least efficient in extracting Fe. The difference between the extraction of Fe by acid and extraction by hydroxylamine was related to the crystallinity of the hydrous iron oxide. As pure iron oxides aged (and crystallized) in the laboratory, Fe solubility in hydroxylamine declined relative to solubility in acetic acid (Table III). In San Francisco Bay sediments, the ratio of hydroxylamine-soluble Fe to acetic acid-soluble Fe increased during the period of maximum runoff to the estuary (27) suggesting the proportion of the Fe in the sediments that was freshly precipitated varied seasonally. This was expected, since periods of heavy runoff are also times of maximum Fe movement from the watershed to the tributaries of the estuary ( ). 

The major requirement for operation of this extractor is that the densities of the solid material and the solvent be different enough so that the particles will settle out. The Model IV extractor reportedly is efficient in extracting finely particulate foods, pharmaceuticals, and spent bleaching earth (146). 

Accounting for efficiencies in extraction columns is much more difficult than for distillation columns, and is not considered here. 

The NER efficiencies in extracts from human HeLa cells of the (+)-trans-, (-)-trans-, and (+)-cis-anti-B[a]P-N2-dG adducts in the identical sequence context (5 -d(CCAT CG CTACC)) (5 -d(GGTAGCGATGG)) embedded in 135mer duplexes are shown in Figure 12.5(a). The lengths of the incision products coincide with those of the marker oligonucleotides around 26-32 nucleotides in length (lane M in Figure 12.5a), which is consistent with dual excision products obtained by the mamma-... 

Under certain idealized conditions, the stage efficiency in extracting some (but not all) cellular materials can be estimated from experimental diffusion data obtained under the conditions of temperature and agitation to be used in the plant. The assumptions are as follows ... 

Although uronium behaves very similarly to guanidinium in the com-plexation discussed, the binding and extraction of urea are a challenging point. Actually, the conversion of urea to uronium requires acidification with, e.g., perchloric acid, which is inconvenient for practical applications. The problem with urea itself is that this neutral molecule forms only weak complexes with various hosts [132,133]. Some initial attempts to overcome the difficulty involved crowns with intra-anular acidic groups and (proton-ated) pyridino crowns [126,134,135], designed to protonate urea upon complexation. However, it was found that these hosts are not efficient in extraction and membrane transport the pyridine compounds failed to protonate urea and have an unfavorable tendency toward self-complexation [136]. Acidic functionalities help to bind urea strongly, but their nature simultaneously manifested itself in unfavorably low host lipophilicity. 

The greatest advantages of LLE, which is stiU employed in routine analysis, are its simpHcity and numerous practical applications. At the same time, this method has many drawbacks, of which the major one is the low efficiency in extracting polar compounds. Even twofold extraction with methylene dichloride of water samples containing phenol and 4-nitrophe-nol results only in 61 and 44% recoveries, respectively [209]. Furthermore, prior to injecting an extract into an analytical column, the excess organic solvent should be evaporated. On the one hand, this may lead to partial loss of volatile compounds, and, on the other hand, it increases the risk of... 

Lab X lacks any evidence of QC. Although the lab reported concentration levels of three semivolatile organics in ppb (parts per billion), no statement about the precision of the analysis is provided. No correlation coefficient is provided. The lab s efficiency in extracting the analytes of... 

The enterohepatic circulation of bile salts involves the cycling of fairly large quantities of material. It has been estimated that the human liver secretes some 30 g of bile salts per day. Of these 30 g, approximately 0.8 g per day is newly synthesized material (4). This emphasizes the efficiency of the intestinal reabsorptive processes. The liver also is remarkably efficient in extracting bile salts from portal blood, as evidenced by the fact that the concentration of bile salts in peripheral plasma is a small fraction of that of portal plasma (5-7). Direct determination of taurocholate and glycocholate extraction by the liver in the dog has been measured by O Maille et al. (8) and found to be 92%. 

Increased efficiency in extraction leads directly to a reduction in material wastage and power ultrasound has been shown to improve systems as diverse as coal slurry benefication on a tonne scale to medicinal compound extraction from plant materials. The classical techniques for extraction are mainly liquid-solid extraction by means of steam and/or organic solvents. All such techniques use relatively high temperatures and thus the energy consumption is very high and decomposition of some compounds may also occur. The use of ultrasound avoids these high temperatures and can result in enhanced component extraction at lower temperatures and in a faster time. 

In addition to solid-liquid collection techniques, in situ sampling methods were developed that contemporarily performed analyte collection and extraction. These systems utilize either sequential or continuous LLE. An example is provided by the aqueous phase liquid extractor (APLE) of Clement and coworkers [22] designed to sample surface water near dump sites where PCDDs and PCDFs were present at level of pg/L. The APLE was capable of extracting up to 200 L water in a single batch process. A spray-bar on the top dispersed a heavier-than-water solvent (methylene chloride) as a fine spray across the surface of the water sample, pushed into the system by a submersible pump. Efficiency in extraction is ensmed by continuous recirculation of the solvent. Devices like the one described avoid the problem of transporting to the laboratory large volumes of sample, but they often remain cumbersome and difficult to be transported. 

Speciality oils may be produced by all the common methods of edible oil isolation and purification. In many cases the oil content is low and combined pressing and solvent extraction methods have been applied. Extraction by supercritical CO also has potential because of its efficiency in extracting low-oil seeds combined with continuously reducing production costs in modern factories. Furthermore, some degree of fractionation according to unsaturation and chain length is possible. Supercritical fluid extraction is recommended for the production of speciality oils because it proceeds at a low temperature, in a low-oxygen atmosphere, is solvent-free, and provides the possibility of aseptic extraction (Manninen et al., 1997). 

The 27-crown-9 system was predicted from models to be a potential host for guanidinium ions, and it has been found that a benzo derivative assists efficiently in extraction of guanidinium salts from aqueous solution into CDCI3, presumably as complex (50). A bis-crown (51) has been designed to accommodate bifunctional... 

Octaphenol 43 is also selective towards the alkaline earths and more efficient in extraction due to its greater number of hydroxyl groups. 

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