Distribution coefficient values, 394 calculation

Vapor-liquid distribution coefficients (/ -values) may be calculated from equations of state using Equations 1.21, 1.23, and 1.25. These calculations require the evaluation of partial properties of individual components, defined as the change in the total solution property resulting from the addition of a differential amount of the component in question to the solution, while holding constant the remaining component amounts and the temperature and pressure. Mathematically, the partial property fl of component i is given by... 

The equilibrium conceirtration of a plasticizer in a polymer can be predicted. The distribution coefficient is calculated from the specific plasticizer concentration in material. It equals to the ratio of plasticizer mass in material 7, mj, to the whole mass of material 1. The dependence of the amoimt of migrated plasticizer through the contact srrrface, M, versus the values of Wjq = mjo/Mi at W20 = = coirst was plotted from experimerttal... 

In Experiment 4B, it is advisable to pool the data for the distribution coefficients and calculate class averages. This will compensate for differences in the values due to experimental error. 

The capacity factors of SN-SiO, for metal ions were determined under a range of different conditions of pH, metal ions concentrations and time of interaction. Preconcentration of Cd ", Pb ", Zn " and CvS were used for their preliminary determination by flame atomic absorption spectroscopy. The optimum pH values for quantitative soi ption ai e 5.8, 6.2, 6.5, 7.0 for Pb, Cu, Cd and Zn, respectively. The sorption ability of SN-SiO, to metal ions decrease in line Pb>Cu> >Zn>Cd. The soi ption capacity of the sorbent is 2.7,7.19,11.12,28.49 mg-g Hor Cd, Zn, Pb, andCu, respectively. The sorbent distribution coefficient calculated from soi ption isotherms was 10 ml-g for studied cations. All these metal ions can be desorbed with 5 ml of O.lmole-k HCl (sorbent recovery average out 96-100%). 

This equation, although originating from the plate theory, must again be considered as largely empirical when employed for TLC. This is because, in its derivation, the distribution coefficient of the solute between the two phases is considered constant throughout the development process. In practice, due to the nature of the development as already discussed for TLC, the distribution coefficient does not remain constant and, thus, the expression for column efficiency must be considered, at best, only approximate. The same errors would be involved if the equation was used to calculate the efficiency of a GC column when the solute was eluted by temperature programming or in LC where the solute was eluted by gradient elution. If the solute could be eluted by a pure solvent such as n-heptane on a plate that had been presaturated with the solvent vapor, then the distribution coefficient would remain sensibly constant over the development process. Under such circumstances the efficiency value would be more accurate and more likely to represent a true plate efficiency. 

Apparent partition coefficient (logZ)) at an ionic strength of / = 0.02M, log P value of the neutral microspecies and the acidic dissociation constant of 5 was calculated (97ANC4143). The distribution coefficient of 5 was determined between 1-octanol and universal buffer in the pH range 3-10 at a... 

Diphenylcarbazide as adsorption indicator, 358 as colorimetric reagent, 687 Diphenylthiocarbazone see Dithizone Direct reading emission spectrometer 775 Dispensers (liquid) 84 Displacement titrations 278 borate ion with a strong acid, 278 carbonate ion with a strong acid, 278 choice of indicators for, 279, 280 Dissociation (ionisation) constant 23, 31 calculations involving, 34 D. of for a complex ion, (v) 602 for an indicator, (s) 718 of polyprotic acids, 33 values for acids and bases in water, (T) 832 true or thermodynamic, 23 Distribution coefficient 162, 195 and per cent extraction, 165 Distribution ratio 162 Dithiol 693, 695, 697 Dithizone 171, 178... 

MD simulations in expHcit solvents are stiU beyond the scope of the current computational power for screening of a large number of molecules. However, mining powerful quantum chemical parameters to predict log P via this approach remains a challenging task. QikProp [42] is based on a study [3] which used Monte Carlo simulations to calculate 11 parameters, including solute-solvent energies, solute dipole moment, number of solute-solvent interactions at different cutoff values, number of H-bond donors and acceptors (HBDN and HBAQ and some of their variations. These parameters made it possible to estimate a number of free energies of solvation of chemicals in hexadecane, octanol, water as well as octanol-water distribution coefficients. The equation calculated for the octanol-water coefficient is ... 

Note that the distribution coefficient depends only on pH, pKa values, and P (not on concentration of sample species). Equation (4.7) is applicable to all lipophilicity calculations. Special cases, such as eq. 4.9, have been tabulated [275],... 

Niflumic acid, which has two pKa values, was studied both pH-metrically and spectroscopically using the shake-flask method [224]. The monoprotonated species can exist in two forms (1) zwitterion, XH 1 and (2) ordinary (uncharged) ampholyte, XH°. The ratio between the two forms (tautomeric ratio) was measured spectroscopically to be 17.4. On assuming that a negligible amount of zwitterion XH partitions into octanol, the calculated micro-log/1 for XH° was 5.1, quite a bit higher than the macro-log/1 3.9 determined pH-metrically in 0.15 M NaCl. It is noteworthy that the distribution coefficient D is the same regardless of whether the species are described with microconstants or macroconstants [275]. 

Results of adsorption experiments for butylate, alachlor, and metolachlor in Keeton soil at 10, 19, and 30°C were plotted using the Freundlich equation. A summary of the coefficients obtained from the Freundlich equation for these experiments is presented in TABLE IV. Excellent correlation using the Freundlich equation over the concentration ranges studied (four orders of magnitude) is indicated by the r values of 0.99. The n exponent from the Freundlich equation indicates the extent of linearity of the adsorption isotherm in the concentration range studied. If n = 1 then adsorption is constant at all concentrations studied (the adsorption isotherm is linear) and K is equivalent to the distribution coefficient between the soil and water (Kd), which is the ratio of the soil concentration (mole/kg) to the solution concentration (mole/L). A value of n > 1 indicates that as the solution concentration increases the sorption sites become saturated, resulting in a disproportionate amount of chemical being dissolved. Since n is nearly equal to 1 in these studies, the adsorption isotherms are nearly linear and the values for Kd (shown in TABLE IV) correspond closely to K. These Kd values were used to calculate heats of adsorption (AH). 

The reaction Kd model, as we can see, differs from the general approach in two ways. The activity rather than the concentration of the dissolved species is carried. Distribution coefficients calculated in the traditional manner, therefore, need to be corrected by a factor of the species activity coefficient. The value of K A for Cd++ in mol g-1 can be determined from a K in cm3 g-1 as,... 

The values of P and selectivity factors are calculated from the experimentally derived solute polarity distribution coefficient for the test solutes ethanol, dioxane, and nitromethane. The solute distribution... 

APEO concentrations in suspended matter samples were similar to the sediment concentrations. From these values, in situ organic carbon corrected suspended matter/water distribution coefficients (log Koc) were calculated. For the separate ethoxymers NP, A9PE0i, A9PE02,... 

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. 

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... 

Application In Analytical And Inorganic Chemistry Knowledge about distribution coefficients is used in analytical chemistry to determine the feasibility of quantitative separation by precipitation. Therefore, D and X are also called separation factors. In order to precipitate 99.8% or more of the primary substance, X must be 3.2 x 10 or smaller. For larger values of X more than one precipitation step is necessary, and the number of steps can be calculated when X is known. 

Thermodynamic calculations based on the compositional dependence of the equilibrium constant are applied to solubility data in the KCl-KBr-H20 system at 25°C. The experimental distribution coefficient and activity ratio of Br /Cl in solution is within a factor of two of the calculated equilibrium values for compositions containing 19 to 73 mole percent KBr, but based on an assessment of uncertainties in the data, the solid solution system is clearly not at equilibrium after 3-4 weeks of recrystallization. Solid solutions containing less than 19 and more than 73 mole percent KBr are significantly farther from equilibrium. As the highly soluble salts are expected to reach equilibrium most easily, considerable caution should be exercised before reaching the conclusion that equilibrium is established in other low-temperature solid solution-aqueous solution systems. 

Table VI summarizes values of the activity coefficient ratio Ygr-/YC].- in the saturated solution for each average solid composition (as calculated from the model of Table II), the calculated provisional equilibrium distribution coefficient (Equation 12) and the provisional equilibrium aqueous solution activity ratio of Br to Cl- (Equation 13) based on the data of Table V.

Data sources given in Haack and McCoy (2004). Values in parentheses are calculated initial liquid compositions for elements like Ir and Re with solid/liquid distribution coefficients that are far from unity, meteorite composition may be different from that of the initial liquid core. 

A chromatography column of 10 mm i.d. and 100 mm height was packed with particles for gel chromatography. The interparticle void fraction e was 0.20. A small amount of a protein solution was applied to the column and elution performed in an isocratic manner with a mobile phase at a flow rate of 0.5 cm min. The distribution coefficient A of a protein was 0.7. An elution curve of the Gaussian type was obtained, and the peak width W was 1.30 cm . Calculate the Hs value of this column for this protein sample. 

Calculate the distribution coefficient K and the 7/s value for this protein sample. 

First, consider the diffusion of an organic compound across the boundary between two environmental systems, A and B. Imagine that at time 1 = 0, the surface of system A (e.g., an air bubble, a silt particle, etc.) is suddenly juxtaposed to a (very large) system B (e.g., the water of a lake, Fig. 18.5a). Mixing in system B is sufficient that the concentration of the selected compound at the boundary of the injected medium is kept at the constant value, Cg. This concentration is different from the initial concentration in A, CA. In system A, transport occurs by diffusion only. We want to calculate the concentration in system A as it evolves in space and time, CA(x,t). For the time being, we will assume that the equilibrium distribution coefficient between A and B is 1. Hence, the concentration of A seeks to change to be equal to that of system B. 

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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