Distribution coefficient compared

The smaller cavity in L2 dissolved in chloroform or toluene resulted in lower distribution coefficients compared to Ll. The order of extraction of the 1 2 metakextractant... 

Fig. 1. Ionic liquid/water distribution coefficients compared to the octanol/water values (log scale). Crosses amino-aromatic compoimds, open triangles neutral compounds or compounds with both acidic and basic substituents, filled-diamond acidic and/or phenolic compounds ( http //www.mariecurie.org/annals/volumeS/berthod.pdf).

By comparing the ratio of the distribution coefficients for a pair of ions, a separation factor (or relative retention) is obtained for a specific experimental condition. 

The above process above could also be performed for the 3-parameter Weibull distribution to compare the correlation coefficients and determine the better fitting distributional model. Computer-based techniques have been devised as part of the approach to support businesses attempting to determine the characterizing distributions... 

The effect of irradiation on the extractability of sulfoxides towards plutonium, uranium and some fission products were studied by Subramanian and coworkers . They studied mainly the effect of irradiation on dihexyl sulfoxide (DHSO) and found that irradiation did not change the distribution coefficient for Ru, Eu and Ce but increases the distribution coefficient for Zr and Pu. When comparing DHSO and tributyl phosphate (TBP), the usual solvent for the recovery and purification of plutonium and uranium from spent nuclear fuels, the effect of irradiation to deteriorate the extraction capability is much larger in TBP. Lan and coworkers studied diphenyl sulfoxides as protectors for the gamma radiolysis of TBP. It was found that diphenyl sulfoxide can accept energy from two different kinds of excited TBP and thus inhibits the decomposition of the latter. 

While there are plenty of methods to predict 1-octanol-water partition coefficients, logP (see Chapters 14 and 15), the number of approaches to predict 1-octanol-water distribution coefficients is rather limited. This is due to a lower availability of log D data and, in general, higher computational complexity of this property compared to that of log P. The approaches to predict log D can be roughly classified into two major categories (i) calculation of log D at an arbitrary pH and (ii) calculation of log D at a fixed pH. 

The permeability coefficient Kpcr is just the flux divided by Cw. It is apparent that the permeability coefficient is linear with P for small distribution coefficients and constant for large P. Thus, for small P the epithelium is the barrier, and for large P the stroma is the barrier. A fit for steroid permeability is shown in Fig. 12, where the regression analysis gave De = 1.4 x 10 9cm2/s and Ds = 2.0 x 10 6cm2/s for 4 = 4 x 10 3 cm and 4 = 3.6 x 10 2 cm [205]. These values for the diffusion coefficients are reasonable compared with those of aqueous gels and lipid membranes. 

To compare the approaches, we repeat the simulation using the reaction K( method (Section 9.1) instead of surface complexation theory. By Equation 21.6, the distribution coefficient K d corresponding to a retardation factor of two has a value of 2.4 x 10-4 mol g 1. Saving this value in dataset Pb Kd.dat , we enter the XlT commands (corn d)... 

Data collected with a simple RPLC procedure has been found to be in good agreement with 1-octanol shake-flask partition or distribution coefficients over a 3.5 log range [64], A chemically bonded octadecylsilane support is coated with 1-octanol. With 1-octanol-saturated buffers as mobile phases, a stable baseline (compared to 1-octanol absorbed on silica) is... 

Model Studies. In model studies of adsorption, one deals with simple, well-defined systems, where usually a single well-characterized solid phase is used and the composition of the ionic medium is known, so that reactions competing with the adsorption may be predicted. It is not a trivial problem to compare the results from such model studies with those from field studies, or to use model results for the interpretation of field data. In field studies, a complex mixture of solid phases and dissolved components, whose composition is only poorly known, has to be considered competitive reactions of major ions and trace metal ions for adsorption may take place, and the speciation of the trace metal ions is often poorly understood. In order to relate field studies to model studies, distribution coefficients of elements between the dissolved and solid phases are useful. These distribution coefficients are of the following form ... 

Distribution coefficients based on adsorption equilibria are independent of the total concentrations of metal ions and suspended solids, as long as the metal concentrations are small compared with the concentration of surface groups. Examples of the Kd obtained from calculations for model surfaces are presented in Fig. 11.1. A strong pH dependence of these Kd values is observed. The pH range of natural lake and river waters (7 - 8.5) is in a favorable range for the adsorption of metal ions on hydrous oxides. 

Comparing Field Data with Laboratory Experiments. Can the distribution of metal ions between particulate and dissolved phases be explained in terms of simple interactions with surfaces on the basis of the obtained surface parameters Can the differences in distribution (as reflected by the distribution coefficients) be explained by different binding properties of the particles ... 

During sorption, the apparent sorption distribution coefficient (fCjpp) can increase by 30% to as much as tenfold between short contact (1-3 days) and long contact times. Desorption likewise often reveals a major slow fraction (10-96%) following a comparatively rapid release. 

The ratio of the distribution coefficients of pertechnetate and perrhenate is about 1.6 to 2, comparable to adjacent rare earth metals. Technetium and rhenium may be separated by ion-exchange chromatography. However, efficient separations require some care and tend to be slow. On the other hand, cation exchange resins adsorb technetiiun only to a negligible extent so that pertechnetate can be rapidly separated from cationic elements . 

Figure 5,65 Garnet-clinopyroxene geothermometric exchange (Fe +-Mg +). Thermodynamic constant K is compared with distribution coefficient K the difference between the two terms represents the effect of interactions in mixtures. Reprinted from J. Ganguly, Geochimica et Cosmochimica Acta, 43, 1021-1029, copyright 1979, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

In this equation a, b and e are constants depending on the physical properties of the material to be separated. In Figure 2 the effective distribution coefficient is plotted over the growth rate on the example of a binary mixture of dodecanole with 3,3% impurity of decanole. One curve represents the measured purities (l ff real) is compared to the curve of k ff for the ideal growth rate and... 

Synthetic peptides have relatively large Stokes radii and hydrodynamic volumes, and smaller diffusion coefficients, compared to low-molecular-weight organic pharmaceutical molecules. As a consequence, the mean pore size and the pore size distribution of the... 

Figure 20.9 Decreasing air-water exchange rate of 02 for a water surface covered with an increasingly thick film of oil. Experimental data by Downing and Truesdale (1955) (dots) are compared with curves calculated from Eqs. 20-39 and 20-40. K0l oM/w is the oil-water distribution coefficient of 02 D0l oi, is molecular diffusivity of 02 in oil. Note that the term containing the air-side exchange velocity, v,a, is neglected.

As shown in the last line of Table 23.5, for PCB33 the three-phase model has little effect on the calculated Kd value. Both values are much smaller than the observed one, although the uncertainty of the latter is large. In contrast, for PCB 185 the new calculated apparent distribution coefficient is reduced as compared to the large particle value of Table 23.4 (from 70 to 45 m3kg l). 

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