Distribution coefficient limiting

Two further examples of type I ternary systems are shown in Figure 19 which presents calculated and observed selectivities. For successful extraction, selectivity is often a more important index than the distribution coefficient. Calculations are shown for the case where binary data alone are used and where binary data are used together with a single ternary tie line. It is evident that calculated selectivities are substantially improved by including limited ternary tie-line data in data reduction. 

Among the properties sought in the solvent are low cost, avadabihty, stabiUty, low volatiUty at ambient temperature, limited miscibility in aqueous systems present in the process, no solvent capacity for the salts, good solvent capacity for the acids, and sufficient difference in distribution coefficient of the two acids to permit their separation in the solvent-extraction operation. Practical solvents are C, C, and alcohols. For industrial process, alcohols are the best choice (see Amyl alcohols). Small quantities of potassium nitrate continue to be produced from natural sources, eg, the caUche deposits in Chile. 

Quality assurance for size exclusion supports is based primarily on the reproducibility of molecular weight calibrations. Although the reproducibility of the exclusion and inclusion limits is important, the distribution coefficients (Ko) of included standards are a better indication of duplication. Table 10.3 (page 314) shows such data for the SynChropak GPC and CATSEC supports. 

Atmospheric sensitivity renders the preparation of ultrapure samples difficult. Nevertheless, vacuum distillation ", ultra-high-vacuum reactive distillation " and crystal growth purification methods " are described zone-refining methods have been applied on a limited scale only - , presumably because of the high volatility of the metals and the unfavorable distribution coefficients. 

The following diagram, given as 6.8.5. on the next page, illustrates further phenomena regarding zone refining. The same situation seen in 6.8.4. occurs for the case at the bottom right of 6.8.5. except that the distribution coefficient is such that the impurity buildup is slower. Nevertheless, simple solid-solution for impurity systems is rarely the norm. The most prevalent case is that of Case III of 6.8.5. Limited solid solution occurs, and we get a two-phase system. 

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. 

According to Eq. (26), which directly ensues from Eq. (22), the distribution potential is the arithmetic mean of the Galvani potentials of cations and anions. These potentials are the ionic constituents of the distribution potential, and in fact, according to Eq. (5) they can be considered as electrical representations of the ionic transfer energies AG or limiting distribution coefficients of the ions, Bj [3]. Here, the reader is referred to the following equations ... 

From the above dependence, and from the definition of the limiting or activity distribution coefficient of electrolyte, i.e., from the equation ... 

The limitation of Eq. (2.1) is that measurement of concentrations of solute within different parts of the membrane is very inconvenient. However, since we can estimate (or possibly measure) the distribution coefficients between bulk water and the membrane, log Kj (the pH-dependent apparent partition coefficient), we can convert Eq. (2.1) into a more accessible form... 

Two distinguishing features of gastrointestinal active and facilitated transport processes are that they are capacity-limited and inhibitable. Passive transcellular solute flux is proportional to mucosal solute concentration (C), where the proportionality constant is the ratio of the product of membrane diffusion coefficient (Dm) and distribution coefficient (Kd) to the length of the transcellular pathway (Lm). 

Legal limitations placed upon the use of all newly launched nonbiodegradable chemicals in Japan require testing each product for accumulation in fish before it can be marketed. These regulations have stimulated corresponding studies about the bioaccumulation of pigments [16]. The distribution coefficient Pow between n-octanol and water may be used to indicate the tendency of a chemical to accumulate in biological systems [17]. 

In this way and by numerical evaluation, Driessens (2) proved that the experimental activities could be explained on the basis of substitutional disorder, according to Equation (27), within the limits of experimental error. It seems, therefore, that measurements of distribution coefficients and the resulting activities calculated by the method of Kirgintsev and Trushnikova (16) do not distinguish between the regular character of solid solutions and the possibility of substitional disorder. However, the latter can be discerned by X-ray or neutron diffraction or by NMR or magnetic measurements. It can be shown that substitutional disorder always results in negative values of the interaction parameter W due to the fact that... 

The constant (Kp) is also known as the distribution coefficient or the partition coefficient. Interestingly, this particular relation [Eq. (a)) was originally derived for ideal solutions only, but it caters for a fairly good description of the behavioural pattern of a number of real-extraction-systems encountered in the analysis of pharmaceutical substances. However, the Partition Law offers the following two limitations, namely ... 

The distribution coefficient is a function of solute concentration and Eq. (35) cannot be solved easily. However, solution exists for the following two limiting cases ... 

The distribution coefficients determined for strontium (at U c) and for barium (at ll C for 3 0 < -log < U.5 and at for all other values of -log Ci) are summarized in Figure 2. Due to the relatively high concentration of strontium in seawater (and hence the relatively high concentration initially in the clay-phase) only limited data for strontium were obtained. The distribution coefficients which were obtained appear to behave similarly to the respective coefficients for barium but are somewhat smaller in magnitude. For solution-phase concentrations on the order of 10"3 mg-atom/ml, the barium coefficients appear to be between 10 and 100 ml/gm, and for solution-phase concentrations on the order of 10 ", the barium coefficients appear to be on the order of 10, as was expected. Furthermore, the coefficients for both strontium and barium are generally consistent with the corresponding data obtained for similar oceanic sediments and related clay minerals found within the continental United States (6,758 13) The... 

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