Distribution coefficients absorption

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%). 

On the basis of data obtained the possibility of substrates distribution and their D-values prediction using the regressions which consider the hydrophobicity and stmcture of amines was investigated. The hydrophobicity of amines was estimated by the distribution coefficient value in the water-octanole system (Ig P). The molecular structure of aromatic amines was characterized by the first-order molecular connectivity indexes ( x)- H was shown the independent and cooperative influence of the Ig P and parameters of amines on their distribution. Evidently, this fact demonstrates the host-guest phenomenon which is inherent to the organized media. The obtained in the research data were used for optimization of the conditions of micellar-extraction preconcentrating of metal ions with amines into the NS-rich phase with the following determination by atomic-absorption method. 

This, as is shown by the theory, is due to the evolution of the heat of absorption, during solute adsorption at the front part of the peak. Conversely, the back of the peak is eluted at a lower temperature than the surroundings throughout the length of the column due to the absorption of the heat of solute desorption. As a result, the distribution coefficient of the solute at the front of the peak, and at a higher temperature, will be less than the distribution coefficient at the back of the peak, at the... 

In the range of operating temperatures and compositions, the equilibrium relations are monotonic functions of temperature of the MSA. This is typically true. For instance, normally in gas absorption Henry s coefficient monotonically decreases as the temperature of the MSA is lowered while for stripping the gas-liquid distribution coefficient monotonically increases as the temperature of the stripping agent is increased. 

A simple rocking device was tested for routine determination of distribution coefficients [9], Sample cells were constructed for two-phase [9] and three-phase [10] systems. The investigators claim that the rocking action causes the shape of each phase to vary slowly and constantly and that the precision associated with the distribution coefficient is similar to that for shake-out methods. The three-phase cell was tested as an in vitro model to simulate factors involved in the absorption process. Rates of drug transfer and equilibrium drug distribution were evaluated under conditions in which one aqueous phase was maintained at pH 7.4 and the other phase was maintained at another pH. 

One of the original concepts governing oral absorption of organic molecules is the pH partition hypothesis . This hypothesis states that only the nonionized form of the drug is able to permeate the membranes of epithelial cells lining the GI tract [26], According to the classical pH-partition theory, permeability is expected to correlate not with the intrinsic partition coefficient but with the so-called distribution coefficient D of the solute [27], where D is defined as ... 

Equilibrium data correlations can be extremely complex, especially when related to non-ideal multicomponent mixtures, and in order to handle such real life complex simulations, a commercial dynamic simulator with access to a physical property data-base often becomes essential. The approach in this text is based, however, on the basic concepts of ideal behaviour, as expressed by Henry s Law for gas absorption, the use of constant relative volatility values for distillation and constant distribution coefficients for solvent extraction. These have the advantage that they normally enable an explicit method of solution and avoid the more cumbersome iterative types of procedure, which would otherwise be required. Simulation examples in which more complex forms of equilibria are employed are STEAM and BUBBLE. 

The free energy is calculated from the stability constant, which can be determined by a number of experimental methods that measure some quantity sensitive to a change in concentration of one of the reactants. Measurement of pH, spectroscopic absorption, redox potential, and distribution coefficient in a solvent extraction system are all common techniques. 

Log D accounts for where the "dose" is, so to speak. The distribution depends on the pKa as well as the pH of the medium. The advantage of using log D is that it incorporates these factors, so, for simple processes such as absorption, distribution coefficients "ej lain" the whole process. An example from our earlier work ( ) is the colonic absorption of acids ranging from phenols to strong carboxylic acids. The absorption rate is given by an equation involving only log D terms. 

Kubinyi ( ) used distribution coefficients of the same series of compounds with his bilinear model for absorption to obtain an even closer correlation. Equation 5. pis a constant related to the model. 

Abiotic model systems, 258t of bioactivity, 258-60 Absorption, distribution coefficients, 228 Absorption rate, equation, 228 Acephate, structure, 97 N-Acetylation, biogenic amines, 114 Actinomycete, anthelminthic activity, 5... 

Another property that is useful in selecting the proper chromatographic conditions (column, mobile phase, etc.) is water solubility or distribution coefficient between a polar (e.g., acetonitrile) and a nonpolar (e.g., -heptane) solvent. Data on water solubility and UV absorption maxima for a large number of NOC can be obtained from Druckrey et al. (25). Eisenbrand et al. (26) reported the distribution coefficients between acetonitrile and n-heptane for several NOC. Those for V-nitroso-dioctylamine, NDMA, and V-nitrosomethyl-2-hydroxyethylamine were reported to be 0.5,17.3, and 32.0, respectively, in this system. This would suggest that in a normal-phase system, using a silica column, these compounds would elute in the same order in which they are mentioned, but the elution order would be reversed in a reversed-phase (C18 column) system. 

We found that absorption of Am3+ is greatly affected by aluminum nitrate. Trivalent Am can be satisfactorily absorbed from 0.1M HN03, but it can not be absorbed from 0.1M HN03 and 0.5M A1(N03)3. In 0.1M HN03 and 0.01M A1(N03)3 solution, the volume distribution coefficient of Am3+ is five times less than in 0.1M HN03. Therefore, if there is a great quantity of Al3+ in the feed solution, it should be removed. 

With the increase of the volume of feed solution, the ratio of H+/NH]J in the resin phase increases and the distribution coefficient of Am and Cm also increases. But separation of Am and Cm becomes poorer(8). In order to improve this, after absorption a washing stage using 0.2M NHi N03-0.015M HN03 is added. In this way, H+/NHj in the resin phase is adjusted to its proper value. 

The different terms of Equation 1 were obtained as follows— /ce, formal potential of the Ce(IV)-Ce(III) couple in the medium, was taken from publications [Ce(IV)]a and [Ce(IV)]o have been measured by direct absorption spectrophotometry [Ce(III)] was calculated by difference between total cerium, titrated by potentiometry, and tetravalent cerium [Bk(IV)]a was calculated from the solvent beta counting, allowing for the measured distribution coefficient of Bk(IV) [Bk(III)] was determined by subtracting the [Bk(IV)]a value from the aqueous counting in all cases [Ce(III)]o and [Bk(III)]o were found to be negligible. 

Material balance calculations on separation processes follow the same procedures used in Chapters 4 and 5. If the product streams leaving a unit include two phases in equilibrium, an equilibrium relationship for each species distributed between the phases should be counted in the degree-of-freedom analysis and included in the calculations. If a species is distributed between gas and liquid phases (as in distillation, absorption, and condensation), use tabulated vapor-liquid equilibrium data, Raoult s law, or Henry s law. If a solid solute is in equilibrium with a liquid solution, use tabulated solubility data. If a solute is distributed between two immiscible liquid phases, use a tabulated distribution coefficient or equilibrium data. If an adsorbate is distributed between a solid surface and a gas phase, use an adsorption isotherm. 

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