Distribution coefficient measurements

Yttrium and the lanthanide FPs, mainly cerium, praseodymium and promethium, will be present in the dissolver solution as trications, which are poorly extracted by TBP/OK. Distribution coefficient measurements show293 that the trisolvates are extracted according to equation (157). 

Wilmarth, W. R., Mills, J. T., Dukes, V. H., Beasley, M. C., Coleman, A. D., Diprete, C. C., and Diprete, D. P. Caustic-side Solvent Extraction Batch Distribution Coefficient Measurements for Savannah River Site High-level Wastes, Sep. Sci. Technol. 38(12,13) (2003), 2637-2645. 

Figure 15.33. In vivo log permeability coefficient of rat brain capillaries (log Rnn) as a function of log octanol/water partition coefficient (logPo/ ), the most commonly used measure of lipophilicity. For compounds in italic, the log distribution coefficient measured at physiological pH was used (logDp/ ). Values denoted with a star are for guinea pig. The strong deviants below the line that are denoted with diamonds are known substrates for P-glycoprotein, a multidrug transporter that actively removes them from the brain.

Sorption Distribution Coefficient. Measurements of DBCP adsorption on soils from the Kunia site at solution concentrations ranging from about 0.25 yg/ml to 290 y g/ml indicated that a linear isotherm described sorption reasonably well when sorption data were fitted with the Freundlich equation, S = KfCeN, the values of N on soils from three depths were 0.92, 0.76 and 0.95 (1 ). Subsequently,... 

For large-scale production the chosen path is liquid-liquid extraction. The technique, using counter-current two-phase extraction procedure, relies on the differential partitioning of soluble rare earth complexes between immiscible aqueous and organic phases. A component will have a distribution coefficient, measured at equilibrium ... 

S, O, or any other medium). Methods used to obtain these activity coefficients have included vapor pressure, solubility, and distribution coefficient measurements. 

Kaplan, D., and et al. 1996. Radionuclide adsorption distribution coefficients measured in Hanford sediments for the low level waste performance assessment project. Pacific Northwest Natl. Lab., Richland, WA. 

The ternary diagrams shown in Figure 22 and the selectivi-ties and distribution coefficients shown in Figure 23 indicate very good correlation of the ternary data with the UNIQUAC equation. More important, however, Table 5 shows calculated and experimental quarternary tie-line compositions for five of Henty s twenty measurements. The root-mean-squared deviations for all twenty measurements show excellent agreement between calculated and predicted quarternary equilibria. 

An eluted solute was originally identified from its corrected retention volume which was calculated from its corrected retention time. It follows that the accuracy of the measurement depended on the measurement and constancy of the mobile phase flow rate. To eliminate the errors involved in flow rate measurement, particularly for mobile phases that were compressible, the capacity ratio of a solute (k ) was introduced. The capacity ratio of a solute is defined as the ratio of its distribution coefficient to the phase ratio (a) of the column, where... 

It is clear that the separation ratio is simply the ratio of the distribution coefficients of the two solutes, which only depend on the operating temperature and the nature of the two phases. More importantly, they are independent of the mobile phase flow rate and the phase ratio of the column. This means, for example, that the same separation ratios will be obtained for two solutes chromatographed on either a packed column or a capillary column, providing the temperature is the same and the same phase system is employed. This does, however, assume that there are no exclusion effects from the support or stationary phase. If the support or stationary phase is porous, as, for example, silica gel or silica gel based materials, and a pair of solutes differ in size, then the stationary phase available to one solute may not be available to the other. In which case, unless both stationary phases have exactly the same pore distribution, if separated on another column, the separation ratios may not be the same, even if the same phase system and temperature are employed. This will become more evident when the measurement of dead volume is discussed and the importance of pore distribution is considered. 

By measuring the retention volume of a solute, the distribution coefficient can be obtained. The distribution coefficient, determined over a range of temperatures, is often used to determine the thermodynamic properties of the system this will be discussed later. From a chromatography point of view, thermodynamic studies are also employed as a diagnostic tool to examine the actual nature of the distribution. The use of thermodynamics for this purpose will be a subject of discussion in the next chapter. It follows that the accurate measurement of (VV) can be extremely... 

Equation (1) can be viewed in an over-simplistic manner and it might be assumed that it would be relatively easy to calculate the retention volume of a solute from the distribution coefficient, which, in turn, could be calculated from a knowledge of the standard enthalpy and standard entropy of distribution. Unfortunately, these properties of a distribution system are bulk properties. They represent, in a single measurement, the net effect of a large number of different types of molecular interactions which, individually, are almost impossible to separately identify and assess quantitatively. 

Although, for most moderators, the surface of a stationary phase in LC can be considered stable at moderator concentrations above about 5%v/v, the results from the same experiments as those carried out by Purnell and his group could still be considered invalid and, at best, would not lead to unambiguous conclusions. Katz et al. [9] avoided this problem by examining liquid/liquid distribution systems using water as one phase and a series of immiscible solvent mixtures as the other and by measuring absolute distribution coefficients as opposed to retention volumes. 

They measured the distribution coefficient of n-pentanol between water and mixtures of -heptane and chloroheptane, -heptane and toluene, and n-heptane and heptyl acetate. The two phase system was thermostatted at 25°C and, after equilibrium had... 

Katz et al. tested the theory further and measured the distribution coefficient of n-pentanol between mixtures of carbon tetrachloride and toluene and pure water and mixtures of n-heptane and n-chloroheptane and pure water. The results they obtained are shown in Figure 17. The linear relationship between the distribution coefficient and the volume fraction of the respective solvent was again confirmed. It is seen that the distribution coefficient of -pentanol between water and pure carbon tetrachloride is about 2.2 and that an equivalent value for the distribution coefficient of n-pentanol was obtained between water and a mixture containing 82%v/v chloroheptane and 18%v/v of n-heptane. The experiment with toluene was repeated using a mixture of 82 %v/v chloroheptane and 18% n-heptane mixture in place of carbon tetrachloride which was, in fact, a ternary mixture comprising of toluene, chloroheptane and n-heptane. The chloroheptane and n-heptane was always in the ratio of 82/18 by volume to simulate the interactive character of carbon tetrachloride. 

Testing the applicability of equation (10) to liquids where the solvent components associate with themselves is experimentally difficult. Katz et al. attempted to do this by measuring the distribution coefficients of some solutes between hydrocarbon and... 

The results obtained by Katz et al. [15] are shown as experimental points on the curves relating the distribution coefficient of the solute against volume fraction of methanol added to the original mixture in Figure 31. Due to the difficulty of measuring the distribution coefficient of each solute between pure water and hexadecane (because of their extremely high retention), the values were obtained from a polynomial curve fit to the data which gave a value for (K) at a = 0. 

Various novel applications in biotechnology, biomedical engineering, information industry, and microelectronics involve the use of polymeric microspheres with controlled size and surface properties [1-31. Traditionally, the polymer microspheres larger than 100 /urn with a certain size distribution have been produced by the suspension polymerization process, where the monomer droplets are broken into micron-size in the existence of a stabilizer and are subsequently polymerized within a continuous medium by using an oil-soluble initiator. Suspension polymerization is usually preferred for the production of polymeric particles in the size range of 50-1000 /Ltm. But, there is a wide size distribution in the product due to the inherent size distribution of the mechanical homogenization and due to the coalescence problem. The size distribution is measured with the standard deviation or the coefficient of variation (CV) and the suspension polymerization provides polymeric microspheres with CVs varying from 15-30%. 

The distribution coefficient can be determined by batch experiments in which a small known quantity of resin is shaken with a solution containing a known concentration of the solute, followed by analysis of the two phases after equilibrium has been attained. The separation factor, a, is used as a measure of the chromatographic separation possible and is given by the equation,... 

In fundamental SEC studies retention is often described in terms of a distribution coefficient. The theoretical distribution coefficient Kg is defined as the ratio of solute concentration inside and outside of the packing pores under size exclusion conditions. The experimental distribution coefficient as defined in Equation 1, is a measurable quantity that can be used to check the theory. 

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