Number of extractions

Hence one extraction with 100 ml. of benzene removes 3 0 g. (or 75 per cent.) of the n-butyric acid, whilst three extractions remove 3 5 g. (or 87-5 per cent.) of the total acid. This clearly shows the greater efficiency of extraction obtainable with several extractions when the total volume of solvent is the same. Moreover, the smaller the distribution coefficient between the organic solvent and the water, the larger the number of extractions that will be necessary. 

For the extraction described in Example 7.14, determine (a) the extraction efficiency for two extractions and for three extractions and (b) the number of extractions required to ensure that 99.9% of the solute is extracted. 

Plot of extraction efficiency versus number of extractions for the liquid-liquid extractio scheme in Figure 7.20. 

Furthermore, the extent to which we can effect a separation depends on the distribution ratio of each species in the sample. To separate an analyte from its matrix, its distribution ratio must be significantly greater than that for all other components in the matrix. When the analyte s distribution ratio is similar to that of another species, then a separation becomes impossible. For example, let s assume that an analyte. A, and a matrix interferent, I, have distribution ratios of 5 and 0.5, respectively. In an attempt to separate the analyte from its matrix, a simple liquid-liquid extraction is carried out using equal volumes of sample and a suitable extraction solvent. Following the treatment outlined in Chapter 7, it is easy to show that a single extraction removes approximately 83% of the analyte and 33% of the interferent. Although it is possible to remove 99% of A with three extractions, 70% of I is also removed. In fact, there is no practical combination of number of extractions or volume ratio of sample and extracting phases that produce an acceptable separation of the analyte and interferent by a simple liquid-liquid extraction. 

There exist a number of other methods for the separation of diamondoids from petroleum fluids or natural gas streams (1) a gradient thermal diffusion process [54] is proposed for separation of diamondoids (2) a number of extraction and absorption methods [53,83] have been recommended for removing diamondoid compounds from natural gas streams and (3) separation of certain diamondoids from petroleum fluids has been achieved using zeolites [56, 84] and a number of other solid adsorbents. 

Some guidelines for predicting the results from distributing a sample between two immiscible solvents are summarized in Table 8.3 [67,68]. The efficiency of an extracting solvent, E, depends primarily on the affinity of the solute for the extracting solvent, Kd) the phase ratio, V, and the number of extractions, n. For simple batchwlse extractions K, should be l u ge, as there is a practical limit to the volume of the extracting solvent and the... 

There are a large number of extraction and clean-up techniques. Some of the more common ones are outlined in Table 4.5. The technique selected will depend on the nature of the sample and of the analyte. 

If D is large, i.e. > 102, a single extraction may effect virtually quantitative transfer of the solute, whereas with smaller values of I) several extractions will be required. The amount of solute remaining in the aqueous phase is readily calculated for any number of extractions with equal volumes of organic solvent from the equation... 

If a substance is soluble in both water and the organic solvent, the result of the extraction depends on the ratio of solubilities if the partition coefficient , e.g. the ratio of the solubility in water to that in ether, is large, correspondingly more ether must be used or the number of extractions must be increased. For this coefficient determines how a substance soluble in two immiscible solvents will distribute itself between them. Whether an aqueous solution should be extracted with a certain amount of ether in one portion or whether it is better to extract several times with smaller portions is... 

LLE can be performed simply using separatory funnels. The partition coefficient should therefore be large because there is a practical limit to the phase-volume ratio and the number of extractions. When the partition coefficient is... 

Properties of the feed solution and the substance to be extracted will decrease the number of extractants that may be applicable. For example, in the extraction of metals, if no anionic metal species are present in the feed solution, there is little point in considering anionic (amine) extractants. On the other hand, if anionic metal species are present, then the amine type best suited to the extraction of the anionic species can be selected, knowing... 

The optimum number of extraction stages is a function of the concentration of the active agent, the flow ratio, the value of unextracted metal, pH, and the interest on the capital investment. 

Successfully examples of applications have been reported for the analysis of pesticides in food using PLE during the extraction step [138-147]. Research had been conducted to optimize the effects of extraction temperature, number of extraction cycles, and various extraction solvent mixture compositions on the extraction effectiveness and recoveries of pesticides fi om food. Besides, cleanup sorbent material(s) can also be imbedded in the extraction cells so that cleanup can also be processed simultaneously with extraction. Although it has the advantages of low solvent consumption and short extraction period, the initial cost is high, large amount of unwanted matrix substances are co-extracted and some unstable compounds, such as endrin yielded low recoveries. 

Three plant growth promoters and five compounds with insecticidal or insect repellant activity have been identified from marine organisms. In addition, a number of extracts have been shown to be active in one or both of the assay systems. 

Phosphate must be applied as fertilizer to the soil. Ideally it is added in quantities sufficient to guarantee optimal yields, but not in excess in order to avoid P transportation into other compartments of the ecosystem. The amount added should be based on an accurate estimation of the plant-available fraction of P already present in a soil.This is an old and difficult task and a large number of extraction methods have been used since intensive land use was practised. Recently methods have been worked out in which a strip of filter paper impregnated with an Fe oxide (2-line ferri-hydrite) is dipped into a soil suspension and the amount of P adsorbed by the paper is taken as being plant-available (Sissingh,1988 Van der Zee et ah, 1987 Sharpley, 1993 Sharpley et ah,1994 Kuo and Jellum, 1994 Myers et ah 1997). Anion and cation resins extracted more P from four heavily fertilized soils than from goethite (Delgado Torrent, 2000). Other oxyanions adsorbed by soil Fe oxides are silicate, arsenate, chromate, selenite ( ) and sulphate. Adsorption of sulphate led to a release of OH ions and was substantially lowered once the Fe oxides were selectively removed (Fig.16.17). 

The steps in this assay are more difficult to follow since a number of extractions take place prior to preparing the final dilution in order to remove excipients ... 

Contaminant properties can also affect treatment costs. The type and amount of contaminants will impact the efficiency of any SVE technology. These impacts include the number of extraction wells, the power of the blower unit, and the length of operation required to achieve project goals. Contaminant properties will also impact the type of ancillary technology(ies) selected (D22449H, p. 4-4). 

Contaminant properties can also affect treatment costs. The type and amount of contaminants will impact the efficiency of SVE, the number of extraction wells, the power of the blower unit. 

The numbers of extracted modules for 298 query chemicals under two different discretization thresholds (3% and 5%) are summarized in Table 1. Two different noise ratios in the module merging process are also tested in both data. 

Saturation of the solution with K2OO3 may reduce the number of extractions necessary. Otherwise continuous extraction may be considered (after addition of more water). 

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