Partition between two phases

Furthermore, most physicochemical properties are related to interactions between a molecule and its environment. For instance, the partitioning between two phases is a temperature-dependent constant of a substance with respect to the solvent system. Equation (1) therefore has to be rewritten as a function of the molecular structure, C, the solvent, S, the temperature, X etc. (Eq. (2)). 

Because micelles are negatively charged, they migrate toward the cathode with a velocity less than the electroosmotic flow velocity. Neutral species partition themselves between the micelles and the buffer solution in much the same manner as they do in HPLC. Because there is a partitioning between two phases, the term chromatography is used. Note that in MEKC both phases are mobile. ... 

EXTRACTIONS. Simple partition between two phases can add another valuable piece of information about the sample. A gas chromatographic analysis before and after extraction indicates the character of the components present. For example, carboxylic acids are readily separated from phenolic compounds by extracting a nonaqueous solution of the sample with dilute aqueous sodium bicarbonate. The carboxylic acids are almost completely transferred to the aqueous phase, whereas the phenolic constituents remain in the organic layer. Additional information on extractants for specific classes can be found in most organic analysis textbooks or inferred from solubility tables. 

Chromatography may be defined as a physical method of separation in which the components to be separated are partitioned between two phases. One of these is stationary(solid or liquid), the -other being mobile(liquid or gas) percolates thru stationary phase(Refs 58, 77 78)... 

When two immiscible solvents are placed in contact, any substance soluble in both of them will distribute or partition between the two phases in a definite proportion. According to the Nernst partition isotherm, the following relationship holds for a solute partitioning between two phases a and b ... 

When solute i partitions between two phases or solvents, it dissolves preferentially in the one having the closest 8 value to its own. Thus if 6, = 8p 8a, the A/i° (for a- p solute transfer) from Eq. 2.36 is negative, driving solute into /3. Conversely, when 6, = 8a 80i A/i° >0, driving solute into a. Thus a compilation of 8s (Table 2.1) can help predict partitioning and aid in the choice of suitable phases to maximize selectivity, particularly the mobile and stationary phases of chromatography [15,24]. 

Since a chromatographic mechanism (solute partitioning between two phases moving relative to one another) is involved in micellar capillary electrochromatography, the theory outlined above for band broadening in electrophoresis does not apply. Theoretical aspects of MCE have been developed by Terabe et al. [36] and by Davis [37]. 

PURPOSE AND RATIONALE Lipophilicity of a compound is associated with many physicochemical and physiological properties. Lipophilicity is described in most cases as partition between two phases (hydrophilic and hydrophobic). Hansch was one of the first to examine the relevance of partition coefficients for the explanation of structural activity relationships. 

Chromatography, a physical method of separation in which the components are partitioned between two phases, was invented simultaneously and independently by American geologist D.T. Day and Russian botanist M.S. Tsvet (Tswett). Their methods and later modifications are described in Vol 3 of Encycl, pp C289 to C298. Qualitative method of separation of ingredients by adsorption was known for centuries. This is described on p C289-R... 

Tin Chemistry Fundamentals, Frontiers and Appiications 5.5.2 Removal of Tin Residues by Partition between Two Phases... 

Separation in Micellar Electrokinetic Chromatography (MEKC) is based on partitioning of the analyte molecules between the aqueous run buffer and the core of micelles, which are contained in the run buffer. The technique is essentially a hybrid between CE and liquid chromatography (LC). The run buffer and micelles are moved through the capillary by an applied electric field. The analytes are dragged with the bulk solution. Similar to LC, the analytes partition between two phases, in this case two mobile phases, the hydrophilic run buffer and the hydrophobic micelles. Unlike other electrophoresis modes, MEKC can distinguish between different neutral compounds according to their hydrophobicity. 

Phase separation is frequently observed in polymer solutions and it is mainly due to their low entropy of mixing. At a state of equilibrium each species of the mixture is partitioned between two phases, namely, the supernatant (extremely dilute) and precipitated (moderately dilute) phases [78]. Theoretical models and experimental techniques have been developed to predict the solubility behavior of polymer solutions, polymer blends, and other related systems [79, 80]. Simple theories only permit a rather qualitative description of this phenomenon [78]. Refined and improved theoretical and semiempirical models allow a more accurate prediction of the demixing phenomena and related thermodynamic properties [57, 81]. 

Chromatography is a separation method in which the components of a sample partition between two phases one of these phases is a stationary bed with a large surface area, and the other is a gas which percolates through the stationary bed. The sample is vaporized and carried by the mobile gas phase (the carrier gas) through the column. Samples partition (equilibrate) into the stationary liquid phase, based on their solubilities at the given temperature. The components of the sample (called solutes or analytes) separate from one another based on their relative vapor pressures and affinities for the stationary bed. This type of chromatographic process is called elution. 

The favourable partitioning of the desired solute between the rafiSnate and the extract phases is dependant on the relative affinities (physical interactions) of the solute species for the two phases. This is expressed through a ratio of the distribution coefficients for the separation of an aliphatic-aromatic mixture, partitioning between two phases, known as the selectivity (5) [22], as defined below ... 

One question that naturally arises is Do the fibers in our samples have the same surface properties and partition between the phases just like a well defined chemical species partition between two phases Or do the fibers that are found in the top phase have different properties from those in the bottom phase To investigate this question we have distributed medium size bleached softwood fibers in the usual way in the basal system. We have then collected fibers from the bottom phase and partitioned them again. The results are given in table 2. 

For systems where / , is zcto and molecular diffusion and partitioning between two phases is the primary mechanism for separation, we can rewrite equation (6.2.29) as follows ... 

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