Percent Extracted

This equation predicts that when Ka, D is nearly equal to Kd, and if is large, the benzoic acid will be extracted into the ether layer D is maximum under these conditions. If, on the other hand, [H ] K, then D reduces to Ko R ]JKa, which will be small, and the benzoic acid will remain in the aqueous layer. That is, in alkaline solution, the benzoic acid is ionized and cannot be extracted, while in acid solution, it is largely undissociated. These conclusions are what we would intuitively expect from inspection of the chemical equilibria. 

Equation 18.8, like Equation 18.1, predicts that the extraction efficiency will be independent of the original concentration of the solute. This is one of the attractive features of solvent extraction it is applicable to tracer (e.g., radioactive) levels and to macrolevels alike, a condition that applies only so long as the solubility of the solute in one of the phrases is not exceeded and there are no side reactions such as dimerization of the extracted solute. 

Of course, if the hydrogen ion concentration changes, the extraction efficiency (D) will change. In this example, the hydrogen ion concentration will increase with increasing benzoic acid concentration, unless an acid-base buffer is added to maintain the hydrogen ion concentration constant (see Chapter 7 for a discussion of buffers). 

In deriving Equation 18.8, we actually neglected to include in the numerator of Equation 18.3 a term for a portion of the benzoic acid that exists as the dimer in the organic phase. The extent of dimerization tends to increase with increased concentration, and by Le Chatelier s principle, this will cause the equilibrium to shift in favor of the organic phase with increased concentration. So, in cases such as this, the efficiency of extraction will actually increase at higher concentrations. As an exercise, derivation of the more complete equation is presented in Problem 12. 

In solvent extraction, the separation efficiency is usually independent of the concentration. 

The fraction extracted, also known as the extraction efficiency, is a measure of the success of an extraction. It is defined as the weight of the analyte found in the extracting solvent after extraction divided by the total weight in the original solvent before extraction. Percent extracted is then defined as 

It may be possible to evaluate the percent extracted by a separate experiment. A solution of the analyte in the original solvent may be prepared such that WOTig (before extraction) is known. Following this, an extraction is performed on this solution using a particular volume of extracting solvent (V ). This volume of extract is then analyzed quantitatively for the analyte by some appropriate analysis technique. Knowing the concentration of the analyte and the volume of extract converted to liters (L ), one can calculate the percent extracted  

239 g of a compound is dissolved in water and this solution is extracted with 50.0 mL of an organic solvent such that the concentration of the compound in the extract is 0.340 g/L, what is the percent extracted  

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To reduce the strong interactions occurring between protein and surfactant with AOT systems during LLE, anionic [8,32] and nonionic surfactants [30,33,142] and other interfacial additives [88,124,143] have been included. An improvement on the percent extraction of protein has also been reported for several of these cases [29,32,33,124,142,143]. 

Percent extraction as the term implies provides directly a measure of effectiveness a solvent or a strippant used in solvent extraction. The mathematical expression of percent extraction is quite simple to derive simply from elementary considerations. This fact, therefore, spares the need to deduce. The expression for percent extraction, P, is shown as ... 

Where Px and PY represent respectively percent extractions X and Y. Working further on the expression of F given above, the following may be written ... 

Table I. Percent Extraction of Imbibed Agents from One Gram of Polyacid Resins Under Synthetic Gastrk (50 mL/lhour) Followed by Intestinal (120 mL/2 boars) Conditions...

Indium, cadmium and silver can be extracted into chloroform as their 8-hydroxyquinoline complexes, and the pH1/2 values for these metals are 2.1, 6.3 and 8.8 respectively. Plot a graph of theoretical percent extraction against pH over the range 0 to 9 for each metal. Deduce the pH of incipient extraction (0.01%) and complete extraction (99.99%) for each metal, and comment on the feasibility of separating each from the other assuming that all the distribution coefficients are sufficiently high. 

Analytical solution of the equations are not available, but these can be solved numerically by using IMSL subroutine IVPRK, which is a modified version of subroutine DVERK based on the Runge-Kutta method. The solution would provide exit concentration of the solute from which percent extraction can be obtained. 

Thus, the most effective separations will involve cases where the target ion interacts strongly with the extractant but is less strongly complexed by the aqueous ligand X. The percent extraction is given by ... 

Percent Extractable Homopolymer, Molecular Weights and Average Number of Cellulose Molecules per Grafted Cellulose. Xanthate Grafting of Various Monomers to Rayon (Taken from Krassig) Ref. 18. 

Monomer (s) Percent Add-on Percent Extractable Homopolymer MWtxlO- of Grafted Side Chains Cellulose Chains per Grafted Side Chain... 

The oils from nutmeg, dill, parsley seed, calamus, crocus, saffron, vanilla beans, sassafras and other plants contain generous amounts of the precursors to the semi-synthetic MDA-like compounds. Recently dried nutmeg is about 15 percent extractable oil. 

Selenium-enriched yeast, regarded as one of the most interesting materials for Se speciation, has also been studied through extraction procedures with water and buffered solutions as well, typically with 30 mmol l-1 tris(hydroxymethyl)amino-methane (Tris)-HCl at pH = 7.0. The investigations performed by several independent research groups almost always led to the same results both water extraction (at 50-90°C for l-2h) and Tris-buffered extraction (at 37°C for 1 h) achieved about 10 percent extraction of Se, the main Se species identified being Se-adenosyl-homocysteine, a small amount of free SeMet and some nonmetabolized, inorganic Se(IV) in the fermentation-media [21, 40, 41, 43, 44]. 

The authors of the studies cited above found that the enzymes used during sample preparation could not completely hydrolyze sample proteins into amino acids. This is partly understandable as both proteinase K and subtilisin are known to show hydrolyzing preference for specific residues of proteins. Accordingly, they do not necessarily arrive at total hydrolysis. At the same time, neither pronase E nor protease XIV could always provide 100 percent extraction of Se from the samples (see Table 19.1). Therefore, alternative methods should be developed in the field of sample preparation to replace enzymatic methods. 

CO Polymerization Effect of Conversion on Low Molecular Weight Macrocyclics. A series of polymerizations of cyclooctene was carried out in a manner similar to that described above, using a constant monomer concentration of 1.57M. The polymerizations were terminated at various reaction times, thus obtaining different conversions. The products were isolated, processed, and analyzed for percent extractable macrocyclics as described previously. 

The DNA concentration in the organic phase can generally be evaluated by the difference in the initial and residual concentrations of DNAs in the feed aqueous solution. However, it should be noted that the amount of DNA extracted into the organic phase is sometimes not in agreement with the reduced amount of DNA from the material source because of the formation of precipitate at the aqueous-organic interface. Thus, in this study, the percent extraction was determined by the direct measurement of the DNA concentration in the organic phase [22]. 

The holocellulose, lignin, and pentosans from Ref. 58 are percent extractive-free wood. f Cross and Bevan cellulose is largely pure cellulose but contains some hemicelluloses. 

Figure 8. Percent extracted into the organic phase as a function of the pH of the aqueous phase a summary of earlier data by the same authors (1).

Figure 9-3 shows how the percent extraction varies with the distribution ratio. Notice that this is a log plot on the Y axis. The effect of varying the amount of extraction solvent is presented in the following example calculation. 

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