Cation-specific distribution between solution

Leodidis and Hatton (43) chose a more theoretical approach and attempted to model the cation specific distribution between reversed micellar phase and bulk aqueous solution. This effect has been observed experimentally with AOT/isooctane systems (45). 

In practice, a set of curves developed by Kemper and Quirk (Fig. 8.10), yields approximate electric potentials as a function of distance from the colloid surface. Such potentials can then be substituted directly into the Boltzmann equation to infer cation and anion distributions. 7/, is the scaled electric potential (equal to —Zef/fkT of Eq. 8,15) at the midplane between interacting colloids, T is the surface charge density in coulombs m-2 (96.5 times the ratio of CEC, in mmoles charge kg-1, divided by the specific surface, in m2 kg-1), Z is the valence of the exchangeable cation, Co is the molar salt concentration in the bulk solution, and x is the distance (in nm) from the midplane between colloids to the plane at which the ion concentration is to be calculated. 

When a metal electrode is placed in an electrolyte solution, an equilibrium difference usually becomes established between the metal and solution. Equilibrium is reached when the electrons left in the metal contribute to the formation of a layer of ions whose charge is equal and opposite to that of the cations in solution at the interface. The positive charges of cations in the solution and the negative charges of electrons in the metal electrode form the electrical double layer [4]. The solution side of the double layer is made up of several layers as shown in Fig. 2.7. The inner layer, which is closest to the electrode, consists of solvent and other ions, which are called specifically adsorbed ions. This inner layer is called the compact Helmholtz layer, and the locus of the electrical centers of this inner layer is called the inner Helmholtz plane, which is at a distance of di from the metal electrode surface. The solvated ion can approach the electrode only to a distance d2. The locus of the centers of the nearest solvated ion is called the outer Helmholtz plane. The interaction of the solvated ion with metal electrode only involves electrostatic force and is independent of the chemical properties of the ions. These ions are called non-specifically adsorbed ions. These ions are distributed in the 3D region called diffusion layer whose thickness depends on the ionic concentration in the electrolyte. The structure of the double layer affects the rate of electrode reactions. 

Based on the concept mentioned above, Shibukawa et al. [ref. 31] have proposed a new model regarding the distribution of ionic solutes in practical exclusion chromatography, where the distribution of sample ion is assumed to be dependent not only on its own physicochemical properties but also on those of the counterion and coion in the eluent. The background eluent ion effect on the distribution coefficients of ionic solutes on neutral hydrophilic gels can be understood on the basis of the ion partition model presented. If there is not any specific interaction such as complex formation between the sample ion s (hereafter sample ion is represented by cation, but, of course, the expressions... 

Anions, together with cations and solvent molecules, are building blocks of the boundary layer that develops in the interface between metal and electrolytic solution. When specifically adsorbed, they alter the charge distribution at the interface and the... 

The exchange of protons between water and an amphoteric metal oxide interface will produce three different types of surface sites (1) unprotonated anionic sites each with a unit negative valence, (2) monoprotonated nonionic sites each with a zero valence, and (3) diprotonated cationic sites each with a unit positive valence. Given sufficient time to reach equilibrium, the proton exchange will produce a S—MO interface in which the number of each type of site and the number of protons in solution becomes constant. To specify the stochiometry of this equilibrium proton distribution, the total number of siuface sites will be designated as nj with the number of each specific type of siuface site designated as (1) n Q, unprotonated anionic sites, (2) soH monoprotonated nonionic sites, and (3) for diprotonated cationic sites. 

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