Solvent from distribution between

ACTIVITY FROM DISTRIBUTION BETWEEN TWO IMMISCIBLE SOLVENTS... 

Impurities or solvent can be bound to crystals via a totally different mechanism. The surface of crystals can adsorb impurities or solvents from the surrounding liquid or gas phases. Consequently, impurities or solvent can distribute between the sohd and liquid/gas phases. Depending upon the nature of the interaction, various adsorption mechanisms have been proposed (Ruthven 1984). 

Liquid-liquid extraction is a process for separating components in solution by their distribution between two immiscible liquid phases. Such a process can also be simply referred to as liquid extraction or solvent extraction however, the latter term may be confusing because it also applies to the leaching of a soluble substance from a solid. 

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... 

Routh and Russel [10] proposed a dimensionless Peclet number to gauge the balance between the two dominant processes controlling the uniformity of drying of a colloidal dispersion layer evaporation of solvent from the air interface, which serves to concentrate particles at the surface, and particle diffusion which serves to equilibrate the concentration across the depth of the layer. The Peclet number, Pe is defined for a film of initial thickness H with an evaporation rate E (units of velocity) as HE/D0, where D0 = kBT/6jT ir- the Stokes-Einstein diffusion coefficient for the particles in the colloid. Here, r is the particle radius, p is the viscosity of the continuous phase, T is the absolute temperature and kB is the Boltzmann constant. When Pe 1, evaporation dominates and particles concentrate near the surface and a skin forms, Figure 2.3.5, lower left. Conversely, when Pe l, diffusion dominates and a more uniform distribution of particles is expected, Figure 2.3.5, upper left. 

Solvent extraction, sometimes called liquid-liquid extraction, involves the selective transfer of a substance from one liquid phase to another. Usually, an aqueous solution of the sample is extracted with an immiscible organic solvent. For example, if an aqueous solution of iodine and sodium chloride is shaken with carbon tetrachloride, and the liquids allowed to separate, most of the iodine will be transferred to the carbon tetrachloride layer, whilst the sodium chloride will remain in the aqueous layer. The extraction of a solute in this manner is governed by the Nernstpartition or distribution law which states that at equilibrium, a given solute will always be distributed between two essentially immiscible liquids in the same proportions. Thus, for solute A distributing between an aqueous and an organic solvent,... 

The partition of different lipids between two immiscible solvents (countercurrent distribution) is useful for crude fractionation of lipid classes with greatly differing polarities. Repeated extractions in a carefully chosen solvent pair increase the effectiveness of the separation but in practice mixtures of lipids are still found in each fraction. A petroleum ether-ethanol-water system can be used to remove polar contaminants (into the alcoholic phase) when interest lies in the subsequent analysis of neutral glycerides, which may be recovered from the ether phase. Carbon... 

The ISE life-time is closely connected with the drift and is at least one year for good electrodes. With some systems, e.g. enzyme electrodes (see chapter 8), the life-time is only a few weeks. It follows from the results of Oesch and Simon [119] that the life-time of electrodes based on ionophores in solventpolymeric membranes depends on the kinetics of dissolution of the ionophore and the plasticiser in the analyte. If both the ionophore and the membrane solvent have distribution coefficients between water and the membrane greater than 10 , then the ISE life-time is at least one year. 

As an illustration of the application of Eq. (2.62), consider the distribution of acetylacetone, having a molar volume of 103 cm mol, between various solvents and water, compared with the distribution between 1 -octanol and water, for which log P= 1.04. The values of log D calculated from Eq. (2.62) at infinite dilution of the acetylacetone are 1.29, 0.80, 0.69, 0.51, and 0.14 for 1-pentanol, chloroform, benzene, carbon tetrachloride, and n-hexane, respectively. The experimental values of log D are 1.13, 0.77, 0.76, 0.50, and -0.05 for these solvents. The order is the same, and even the numerical values are not very different, considering that solute-solvent interactions other than the work required for cavity formation have not been taken into account. 

The product was extracted with ethyl ether and after evaporation of the solvent the dry residue was recrystallized from CCl AtCHjCOOH was identified by ion-exchange chromatography. Its dissociation constant determined by the measurement of its distribution between... 

The approach to calculate the van der Waals and cavity terms from the molecular surface areas can be used for the calculation of partition coefficients. The results show that for the distribution of hydrocarbons between water and n-octanol the calculated partition coefficient is linear in carbon number. Qualitatively similar data are obtained for the distribution between other solvents and water and the results can be used to predict the retention in liquid>liquid chromatography. On the other hand, if retention in RPC occurs due to reversible binding at the surface of the stationary phase, the significant parameter is not the total surface area of the eiuite but rather the net decrease in the molecular surface area of the stationary phase ligates and that of the eiuite upon binding, i.e., the contact area in the complex. 

SMART (Solvent Measurement, Assessment, and Revamping Tool) is a software program that allows assessment of solvents used for batch processing based on both empirical data and property estimation methods (Modi et al., 1996). This system includes a new conjugation based method for the estimation of reaction rates in solution, which is based on the concept that the absolute reaction rate coefficient can be obtained from a function dependent on the change in molecular charge distribution between reactants and activated complex (Sherman et al., 1998). Table 9.2 provides a list of solvent substitution resources available on the World Wide Web. 

Elution in reversed-phase chromatography is often carried out using a gradient, produced from water and some water-miscible organic solvent. The solute components are thus distributed between the stationary and mobile phases mainly on the basis of their polarities. In reversed-phase chromatography hydrophilic compounds elute before hydrophobic ones. 

Extraction is a process for separating components in solution by their distribution between two immiscible phases. Such a process can also be called liquid extraction or solvent extraction. The former term may be confusing because it also applies to extraction by solid solvents. Since extraction involves the transfer of mass from one phase into a second immiscible phase, the process can be carried out in many ways. The simplest example involves the transfer of one component from a binary mixture into a second immiscible phase — extraction of an impurity from wastewater into an organic phase. In some cases, a chemical reaction can be used to enhance the transfer, e.g., the use of an aqueous caustic solution to remove phenolics from a hydrocarbon stream. 

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