Distribution ratio and separations

On the other hand, Dyrssen and Liem (1960) report (table 7) greater variation in both distribution ratios [for americium and europium extraction by dibutyl phosphoric acid (HDBP)] and in separation factors as a function of diluent. The separation factors and distribution coefficients are correlated (more or less consistently) inversely with the distribution ratio of the extractant between the phases. In this system, the largest separation factors are observed in n-hexane, chloroform, and carbon tetrachloride. Diluents capable of direct coordination (i.e., those possessing potential oxygen-donor atoms) are correlated with reduced distribution ratios and separation factors. The observations of greater separation factors in non-complexing diluents suggest that more effective separation is observed when the inner-coordination sphere of the hydrophobic complex is not disturbed. 

The effect of aqueous complex formation on distribution ratios and separation factors can be readily understood in terms of equilibria already discussed. For the simplest case in which the aqueous metal complexes are not extracted into the counter-phase, the observed distribution ratio will represent a balance between the two phase extraction reaction, and the homogeneous complexation equilibria in the aqueous phase. 

Distribution ratios and separation factors for americium/ europium extraction by 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione/toluene (0.0297 M)/0.1 M NaClO as a function of 4,7-diphenyl-l,10-phenanthroline (synergist) from Ensor et al. (1988). 

Although Peligot observed in 1842 that uranyl nitrate is soluble in ether, it was not until materials of high purity were needed for nuclear reactors that extensive applications and developments, both industrial and analytical, were made. The literature on applications of liquid-liquid extraction (solvent extraction) is extensive for details of the various procedures the reader is referred to the original papers and to compilations. " This chapter examines separations involving distribution of a solute between two immiscible phases and chemical equilibria of significance to the distribution ratio. Batch, countercurrent, and continuous liquid-liquid extractions are described in turn, followed by consideration of the factors governing the distribution ratio and finally by some illustrative applications. 

In general, with a sufficiently large equilibrium constant (distribution ratio) and a rapid rate of attainment of equilibrium, quantitative transfer from one phase to another can be made in a single stage. For such highly favorable systems, batch liquid-liquid extractions can be used in which one phase is equilibrated with several successive fresh portions of a second phase. Such batch separations are most effective when one component remains quantitatively in one phase while another distributes itself between the two phases. 

Twenty milliliters of an aqueous solution of 0.10 M butyric acid is shaken with 10 mL ether. After the layers are separated, it is determined by titration that 0.5 mol butyric acid remains in the aqueous layer. What is the distribution ratio, and what is the percent extracted ... 

Often, it is not possible to extract one solute quantitatively without partial extraction of another. The ability to separate two solutes depends on the relative magnitudes of their distribution ratios. For solutes A and B, whose distribution ratios are separation factor / is defined as the... 

In liquid chromatography (LC, TLC and HPLC) the mobile phase and stationary phase both influence the distribution ratio and therefore LC separations can be influenced primarily by choice of stationary phase and modification of the mobile phase composition. 

The ability of a stationary phase to separate two components A and B, where B is the more strongly retained component, is determined by their relative partition or distribution ratios and hence their retention factors for a given Stationary phase. The separation factor (a) is therefore a function of the relative retention of each component by a stationary phase. 

Mobile phase transports the solutes or components to be separated through a column or plate of stationary phase material. The solution properties of a liquid mobile phase compete with the retention forces of the stationary phase to determine the distribution ratio and hence elution time. In GC the gaseous mobile phase transports components in the vapour phase. 

The course of an ion exchange separation can be described in terms of D, the distribution ratio, and the percent E, or percent exchanged. D will be written as the ratio of ion concentration in the resin phase, millimoles per gram, to the ionic concentration in the aqueous phase, millimole per milliliter (molarity). 

On an industrial scale, the batch method is usually replaced by continuous counterflow contactors, and to obtain high distribution ratios or separation... 

The general theory of countercurrent distribution is still of general interest since manual liquid-liquid extraction remains a common laboratory technique. In addition, countercurrent distribution models often provide a starting point for the explanation of separations by chromatography and continuous liquid-liquid extraction processes. A favorable feature of countercurrent distribution systems is that separations are completely predictable, once the solute distribution ratios and the phase ratio are known. 

Example 2.2.2 In the flash expansion desalination process (also called the flash vaporization process), cold sea water, heated to a temperature of 121 °C at the corresponding saturation pressure in a preheater, is allowed to enter a flash chamber where the temperature is 38 °C and the pressure is much lower at the corresponding saturation pressure. This produces some pure water vapor and a concentrated brine. In practical processes, the vapor mass flow rate produced can be at most 20% (Silver, 1966) of the feed brine mass flow rate. If the brine feed has 3.5 wt% salt, describe the separation achieved with the separation factors, extent of separation, distribution ratio and equilibrium ratio for two vapor flow rates expressed as a percentage of the feed brine mass flow rate (a) 20 wt%, (b) 10 wt%. 

Equation (5) is regarded as a fundamental equation of column chromatography as it relates the retention volume of a solute to its distribution ratio. Planar separations (PC and TLC). Separations are normally halted before the mobile phase has travelled completely across the surface, and solutes are characterized by the distance they have migrated relative to the leading edge of the mobile phase (solvent front). A solute retardation factor, Rf, is defined as... 

Extraction Between Two Phases When the sample is initially present in one of the phases, the separation is known as an extraction. In a simple extraction the sample is extracted one or more times with portions of the second phase. Simple extractions are particularly useful for separations in which only one component has a favorable distribution ratio. Several important separation techniques are based on simple extractions, including liquid-liquid, liquid-solid, solid-liquid, and gas-solid extractions. 

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. 

The problem with a simple extraction is that the separation only occurs in one direction. In a liquid-liquid extraction, for example, we extract a solute from its initial phase into the extracting phase. Consider, again, the separation of an analyte and a matrix interferent with distribution ratios of 5 and 0.5, respectively. A single liquid-liquid extraction transfers 83% of the analyte and 33% of the interferent to the extracting phase (Figure 12.1). If the concentrations of A and I in the sample were identical, then their concentration ratio in the extracting phase after one extraction is... 

Chromatographic separations are accomplished by continuously passing one sample-free phase, called a mobile phase, over a second sample-free phase that remains fixed, or stationary. The sample is injected, or placed, into the mobile phase. As it moves with the mobile phase, the sample s components partition themselves between the mobile and stationary phases. Those components whose distribution ratio favors the stationary phase require a longer time to pass through the system. Given sufficient time, and sufficient stationary and mobile phase, solutes with similar distribution ratios can be separated. 

Thus far all the separations we have considered involve a mobile phase and a stationary phase. Separation of a complex mixture of analytes occurs because each analyte has a different ability to partition between the two phases. An analyte whose distribution ratio favors the stationary phase is retained on the column for a longer time, thereby eluting with a longer retention time. Although the methods described in the preceding sections involve different types of stationary and mobile phases, all are forms of chromatography. 

Two solutes, A and B, with distribution ratios of 9 and 4, respectively, are to be separated by a countercurrent extraction in which the volumes of the upper and lower phases are equal. After 100 steps, determine the 99% confidence interval for the location of each solute. 

The physical process of Hquid—Hquid extraction separates a dissolved component from its solvent by transfer to a second solvent, immiscible with the first but having a higher affinity for the transferred component. The latter is sometimes called the consolute component. Liquid—Hquid extraction can purify a consolute component with respect to dissolved components which are not soluble in the second solvent, and often the extract solution contains a higher concentration of the consolute component than the initial solution. In the process of fractional extraction, two or more consolute components can be extracted and also separated if these have different distribution ratios between the two solvents. 

Another TSK combination (precolumn -I- PWM -I 6000 -I 5000 -I- 4000 -I-3000) was tested on differences in separation performance between individual narrow distributed samples and mixtures of several narrow distributed samples. The result is summarized in Eig. 16.31 within experimental error the summed chromatograms (theory) of four narrow distributed glucans (dextran) match perfectly with the experimentally determined chromatogram of the mixture. The (theory/experimental) ratio, plotted for quantification of the match, in-... 

X 0.75 cm) Ve i = 28 ml = 50 ml eluent 0.05 M NaCI flow rate 0.80 ml/min detection Optilab 903 interferometric differential refractometer applied sample mass/volume 200 /tl of 2-mg/ml aqueous solutions sum of individual chromatograms (theory —) and (theory/experimental) ratio (—) plotted for quantification of deviations in separation performance between narrow distributed samples and broad distributed samples. 

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