Partitioning between phases

Obviously, construction of a mathematical model of this process, with our present limited knowledge about some of the critical details of the process, requires good insight and many qualitative judgments to pose a solvable mathematical problem with some claim to realism. For example what dictates the point of phase separation does equilibrium or rate of diffusion govern the monomer partitioning between phase if it is the former what are the partition coefficients for each monomer which polymeric species go to each phase and so on. 

Another area of rapid growth for particle separation has been that of Field-Flow Fractionation (FFF) originally developed by Giddings (12,13>1 1 ) (see also papers in this symposium series). Like HDC, the separation in field-flow fractionation (FFF) results from the combination of force field interactions and the convected motion of the particles, rather than a partitioning between phases. In FFF the force field is applied externally while in HDC it results from internal, interactions. 

The problem of transport of molecules through swollen gels is of general interest. It not only pertains to catalysis, but also to the field of chromatographic separations over polymeric stationary phases, where the partition of a solute between the mobile phase (liquid phase) and a swollen polymeric stationary phase (gel phase) is a process of the utmost importance. As with all the chemical and physicochemical processes, the thermodynamic and the kinetic aspect must be distinguished also in partition between phases. 

Note that a. B may reflect either kinetic or equilibrium isotope partitioning between phases A and B. As discussed in the previous chapter, a -B for Fe/ Fe ratios typically varies between 0.997 and 1.003 (Chapter lOA Beard and Johnson 2004). In general, we will describe isotopic fractionations using A. b, following standard definitions ... 

From Fig. 7.1, it may be observed that residual alkalinity initially increases with water evaporation, concomitant with a pH increase, and that negative residnal alkalinity and pH decrease even if alkalinity is due to any kind of anions. Because evaporation leads to a change in the quality of water, the water properties as a solvent for organic contaminants are also changed. This fact should be considered when dealing with contaminant partitioning between phases. 

In the definition of c, one must generally assume that any chemical component is free to penetrate into any phase, even if the partitioning between phases varies strongly from component to component. Hence, c is the number of independent chemical components found in any phase, to account for the limiting case in which different chemical components partition completely (within limits of experimental detection) into different phases. 

Suppose that solute S is partitioned between phases 1 and 2, as depicted in Figure 23-1. The partition coefficient, K, is the equilibrium constant for the reaction... 

Abraham, M.H., and A.J. Leo. 1995. Partition between phases of a solute that exists as two interconverting species. /. Chem. Soc. Perkin Trans. 2, 1839-1842. 

Fluorous biphase reactions have been reviewed extensively in the past few years, and most important types of reaction may now be conducted under fluorous conditions [46,51], However, partitioning of catalysts and reagents into the fluorous phase is seldom perfect - even a loss of 1-2% of an expensive catalyst may be unacceptable. Solubility and partitioning between phases relies on a complex balance of properties and interactions, and rather than simply adding more fluorocarbon chains to a catalyst (which is a common approach to the problem of leaching of catalyst from the fluorous phase), studies have indicated that the partition coefficients of fluorous compounds may better be optimised by... 

Chemical properties that reflect the tendency of a chemical to partition between phases have been constructed specifically for environmental fate applications. These specialized properties are known as partition coefficients. The parameter that is a measure of a chemical s tendency to partition between water and air is known as the dimensionless Henry s constant (KH), determined by the ratio of the... 

The physical meaning of Eq. [42] is tied to the interpretation of some of the terms, some being convoluted. The A term can be associated with dispersion interactions an increase in surface area suggests an increase in dispersion interactions (attractions) and, thus, increased solubility in octanol that in turn results in enhanced Pq/w values. A similar interpretation holds if one associates p /V with dipolarity/polarizability effects. The positive sign on the HBA term ( Umin) fot the solute suggests that the HBD acidity of water is less important than the HBA basicity of water for those molecules partitioning between phases. This implies that increased solute HBD acidity would increase the solute-water interaction. 

Hart S. R. and Ravizza G. E. (1996) Os partitioning between phases in Iherzolite and basalt. In Earth Processes Reading the isotopic Code, Geophysical Monograph 95 (eds. A. Basu and S. R. Hart). American Geophysical Union, Washington, DC, pp. 123-134. 

Typical examples of one-phase techniques are filtration and dialysis. The membrane is porous, so there is a liquid (or gas) contact through the pores between the donor and acceptor phases, which are of similar chemical composition (i.e., both are either aqueous, organic, or gaseous). There is no phase boundary, and therefore, no partition between phases. Thus, physical and not chemical properties govern the process. This review will not consider one-phase systems further. Eor information on dialysis, especially its analytically interesting version microdialysis, see Refs. [23,24]. 

The use of inverse gas chromatography (IGC) to study the properties of polymers has greatly increased in recent years (1,2). The shape and position of the elution peak contain information about all processes that occur in the column diffusion of the probe in the gas and the polymer phases, partitioning between phases, and adsorption on the surface of the polymer and the support. Traditional IGC experiments aim at obtaining symmetrical peaks, which can be analyzed using the van Deemter (3j or moments method (4). However, the behavior of the polymer-probe system is also reflected in the asymmetry of the peak and its tail. A method that could be used to analyze a peak of any shape, allowing elucidation of all the processes on the column, would be of great use. 

Do chemical species of interest partition between phases ... 

In this equation,. r . r, represent the molar fractions of the selected diffusing species in its partition between phases 1 and 2, and D, denote the respective diffusion coefficients. 

Vapor pressure Partitioning between phases solubility of a gas in a liquid sorption of a solute in a fluid onto a sorbent Chemical reaction equilibrium Electric charge Phase change solid/liquid liquid/gas Diffusivity Ionic mobility Molecular size and shape... 

Extraction Partitioning between phases Immiscible liquid... 

Adsorption Partitioning between phases Solid sorbent... 

Absorption Partitioning between phases Non-volatile liquid... 

Separation processes use two primary mechanisms for performing the separation partitioning between phases (equilibrium) or relative motion of various chemical species (rate). 

Phase equilibrium information characterizes partitioning between phases for a system and is important for describing separation processes. For equilibrium-limited processes, these values dictate the limits for separation in a single stage. For mass transfer-limited processes, the partitioning between phases is an important parameter in the analysis. The data can be presented in tabular form. But this approach is restricted in application, since an analysis typically requires phase equilibrium values that are not explicitly listed in the table. So, graphical representation and computational methods are usually more useful. 

The dynamics of partitioning between phases, and the role of interstitial water in sediments and soils. Specific attention should be directed to the quantitative significance of associations between xenobiotics and both organic and inorganic components of the soil andsedimentphasesandtheextenttowhichtheseprocessesarereversible. 

Either partitioning between phases or adsorption interactions between solute and polar bonded phase. 

Does this pH adjustment have any effect on the partitioning of HOAc between immiscible phases By definition, only neutral HOAc can partition between phases. The value for the partition ratio must be preserved based on the thermodynamic arguments put forth earlier. This must mean that the concentrations of HOAc in the ether phase must be reduced due to the pH adjustment because the concentration of undissociated HOAc in the aqueous phase has also been reduced. This is illustrated for the HOAc, only, in Figure 3.3. Our model assumes that the only chemical form of acetic acid in the ether phase is HOAc and that only acid dissociation of HOAc occurs in the aqueous phase. Because Kd accounts only for imdissodated forms of... 

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