Partitioning of ions

When a solute is added to one of the two solutions, it will difFuse into the other, and after a certain time equilibrium will be established. The distribution of the solute between the two phases is known as partitioning, and can be determined from standard thermodynamics. 

When the two solutions are in equilibrium the electrochemical potential of each species must be the same in both phases  

The partitioning of ions is not so simple, since each solution must be electrically neutral (with the exception of a thin boundary layer at the interface). As an example we consider the case where a single salt is partitioned between the two phases for simplicity we assume that the cation and the anion have the same charge number . We denote the cation by the index +, and the anion by -. Applying the equilibrium condition Eq. (12.1) to both ions gives for the difference in inner potentials  

Since each solution must be electrically neutral anions and cations have the same concentrations in the bulk  

All quantities in Eq. (12.6) are measurable The concentrations can be determined by titration, and the combination of chemical potentials in the exponent is the standard Gibbs energy of transfer of the salt, which is measurable, just like the mean ionic activity coefficients, because they refer to an uncharged species. In contrast, the difference in the inner potential is not measurable, and neither are the individual ionic chemical potentials and activity coefficients that appear on the right-hand side of Eq. (12.3). 

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Japanese lacquer, have also been employed. The partitioning of ions into this phase is selectively aided by either ion exchangers or neutral carriers. 

The equilibrium partition of ions present in the system gives rise to the equilibrium Galvani potential difference A (p = y (w) — (o) between the phases w and o (Nernst potential) [7,8]... 

Dissociation in a field-free region (FFR) not only causes partitioning of ion kinetic energy (Eq. 4.10), but also goes with partitioning of momentum p... 

Protein partitioning and ion co-partitioning in the two-phase system was also modeled by Fraaije et al. [177]. Experiments performed on the partitioning of cytochrome C in TOMAC-octanol-isooctane provided good agreement with the model. At the pH of maximum solubiHzation, no co-partitioning of ions occurred. At pH values below and above the maximum solubiHzation pH, there was exclusion and inclusion, respectively of electrolytes. 

Holt, C. (1981) Some principles determining salt composition and partitioning of ions in milk. J. Dairy Set., 64, 1958-64. 

Alkaline Earth Oxides. If a trivalent lanthanide is substituted for Ca + in CaO (5) or a Cr3+ is substituted for a Mg2+ in MgO (6), the extra positive charge is compensated by a cation vacancy as described earlier. The vacancy can be in a near neighbor position or it can be very distant from the probe ion (7-10). If another ion like Na+ is in the cation site, it can serve as a charge compensation for the probe ion either as a nearby ion or distantly. This case is coupled ion substitution that commonly affects the partitioning of ions into different mineral phases (11). One can envision many other ions that could also affect the local environment or the probe ion. 

Interface between two liquid solvents — Two liquid solvents can be miscible (e.g., water and ethanol) partially miscible (e.g., water and propylene carbonate), or immiscible (e.g., water and nitrobenzene). Mutual miscibility of the two solvents is connected with the energy of interaction between the solvent molecules, which also determines the width of the phase boundary where the composition varies (Figure) [i]. Molecular dynamic simulation [ii], neutron reflection [iii], vibrational sum frequency spectroscopy [iv], and synchrotron X-ray reflectivity [v] studies have demonstrated that the width of the boundary between two immiscible solvents comprises a contribution from thermally excited capillary waves and intrinsic interfacial structure. Computer calculations and experimental data support the view that the interface between two solvents of very low miscibility is molecularly sharp but with rough protrusions of one solvent into the other (capillary waves), while increasing solvent miscibility leads to the formation of a mixed solvent layer (Figure). In the presence of an electrolyte in both solvent phases, an electrical potential difference can be established at the interface. In the case of two electrolytes with different but constant composition and dissolved in the same solvent, a liquid junction potential is temporarily formed. Equilibrium partition of ions at the - interface between two immiscible electrolyte solutions gives rise to the ion transfer potential, or to the distribution potential, which can be described by the equivalent two-phase Nernst relationship. See also - ion transfer at liquid-liquid interfaces. 

A characteristic of immobilized enzymes that is often ignored is the potential partitioning of ions and substrates and/or products due to electrostatic potentials or hydrophobic moments. This factor could be used to advantage, for example, if the optimal conditions for enzyme activity do not match those of the process stream. To use the example cited earlier, a succinamidopropyl surface was shown by electrostatic partitioning of ions and independent chemical analysis to have 96 ymol charged groups/g dry beads (25). Attachment of 2 ymol trypsin/g did not significantly alter this characteristic. 

Most often Pj values are 3 to 5 decades smaller than the corresponding values the differences can be larger, e.g. for salicylic acid (19) which contains two acidic groups (Figure 25) [463], but also much smaller, e.g. for chenodesoxycholic acid, which forms micelles [462], or in the presence of lipophilic counter ions, e.g. for salicylic acid in the presence of tetrabutyl-ammonium bromide (20) (Figure 26) [463]. Lipophilicity and polarizability of the counterion have a significant influence on the partitioning of ion pairs e.g. [465 — 468]). 

There are several types of electroactive polymers which have found application in chemical sensors. Thus, a large group of ion selective electrodes uses polymer matrices which host specific binding sites, called ionophores or ion exchangers. There is a selective partitioning of ions... 

Polysoap PSI62 (Myy, = 2x10 ) was dissolved in its acid form in n-octanol saturated with water. The 1% wt polymer solution was transferred to an aqueous solution containing hydrogen and alkali metal chlorides. The partitioning of ions between the two phases was examined according to equilibria (6) and (7) ... 

Kurella, G. A., 1969, The difference of electric potentials and the partition of ions between the medium and vacuole of the alga, in Glass Microelearodes M. Lavallce, O. F. Schanne, and N. C. Hebert, eds.), John Wiley and Sons, New York. 

Liquid-liquid (or solvent) extraction is a separation technique that depends on the partition of ions between two immiscible liquid phases, one of which is usually... 

The influence of electrolytes on bubble coalescence in both aqueous and non-aqueous systems is ion specific. The available evidence suggests that ion specific effects at the air-water interface are strongly correlated with the partitioning of ions in the interfacial region. Ion partition coefficients determined from surface tension data correlate well with the empirically assigned a and parameters used to predict bubble coalescence inhibition. Bubble coalescence is inhibited when there is an accumulation of both ions at the interface or a removal of both ions from the interface, though the precise mechanism of inhibition remains elusive. 

In the zero point of chaise there is no double layer due to inhomc eneous partition of ions and A 9 = Xi2 Introducing the concentration dependence of the chemical potential in the solution, we may transform (94) into... 

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