Electrolytic, in ion exchangers

Graham-Uranoff They studied multicomponent diffusion of electrolytes in ion exchangers. They found that the Stefan-Maxwell interaction coefficients reduce to limiting ion tracer diffusivities of each ion. 

The swelling pressure is proportional to the concentration of the fixed ions and inversely proportional to the concentration of the electrolyte. In ion-exchange membranes with high fixed ion concentrations and dilute solutions it can reach very high values well in excess of 100 bars [13]. 

Breadmore, M. C., Macka, M., and Haddad, P. R., Manipulation of separation selectivity for alkali metals and ammonium in ion-exchange capillary electrochromatography using a suspension of cation exchange particles in the electrolyte as a pseudo stationary phase, Electrophoresis, 20, 1987, 1999. 

In Section 15.6, the retention of proteins in ion exchange chromatography is discussed. The ions in the surrounding electrolyte form an electrical double layer around a charged macromolecule, e.g., a protein. The interaction between a protein and an oppositely charged surface can, therefore, be described as taking place between two overlapping double-layer systems. 

Monomer and polymer electrolytes containing ion-exchangeable functional groups, (I), and an ionic Uquid functional group, (II), were prepared by Best et al. (1) and used in fuel cells. 

MSA and other lower alkanesulfonic acids are useful for plating of lead, nickel, cadmium, silver, and zinc (409). MSA also finds use in plating of tin, copper, lead, and other metals. It is also used in printed circuit board manufacture. In metal finishing the metal coating can be stripped chemically or electrolytically with MSA. MSA also finds use in polymers and as a polymer solvent and as a catalyst for polymerization of monomers such as acrylonitrile. MSA also finds use in ion-exchange resin regeneration because of the high solubility of many metal salts in aqueous solutions. 

There are some cases where a reaction, that is, the formation or dissolution of a chemical bond, is involved along with ion exchange phenomena (Helfferich, 1983). Examples of this are acid-base neutralization, dissociation of weak electrolytes in solution or weak ionogenic groups in ion exchangers, complex formation, or combinations of these (Table 5.2). With some of these, very low apparent D in ion exchangers have been noted. 

Reichenberg. D, (1957). Properties and behavior Kinetics, electrolyte penetration, and absorption of nonelectrolytes. In Ion Exchangers in Organic and Biochemistry (C. Calmon and L. R. E. Kressman, eds.), pp. 66-85. Wiley, New York. 

Ion exchange can be an effective method for the controlled release of ionizable drugs that are coupled with the oppositely charged ionic groups on a polymer matrix, as in ion-exchange resins used in gastrointestinal (Gl) applications. The drug release from such a system depends on the ionic environment, that is, pH and electrolyte concentration within the Gl tract, as well as the properties of the resin (5). 

In an electrolyte solution the current is carried by both ions. However, cations and anions usually carry different portions of the overall current. In ion-exchange membranes the current is carried preferentially by the counterions. 

When dissimilar metals or electrodes are immersed in an electrolytic solution with common ions, an electromotive force (EMF) develops between the electrodes. This is the principle behind formation and working of galvanic cells. The EMF is characteristic of the free energy change in ion exchange (i.e. the cell reaction). 

The application of ion-exchange dynamics for the determination of HETP or HTU values should be studied in ion-exchange systems characterized by invariable static and kinetic parameters such as ion-exchanger swelling, electrolyte sorption, separation coefficient, and interdiffusion coefficients in solution and resin phases over experimentally investigated ranges of component variation. 

As Eq. (1.15) can be used in many ion-exchange systems to describe the effect of the concentration of electrolyte (polar solvent), the elution volumes in ion-exchange chromatography with linear gradients of the concentration of a salt or of a buffer can be calculated using the same Eq. (1.36) as in NPC systems. 

Concentration of dilute electrolytes An ion-exchange column is effective for collecting ionic substances from large volumes of dilute solutions. By elution employing a small volume of solution, a considerable concentration effect can be achieved. As examples may be cited the concentration of cations and anions in natural waters, beryUium from bones, copper from milk, and silver in atmospheric precipitation. Ion-exchange beads have been proposed as chemical microstandards since they can retain small measurable quantities (10 g) of ions such as sodium, potassium, calcium, and uranium. It is highly desirable that the beads be uniform in size and homogeneous in the trace constituent. 

Equations (3.36) and (3.37) predict that retention in ion-exchange chromatography decreases with increasing concentration of counter ions in the mobile phase. Thus retention is optimized by appropriate choice of the type and concentration of electrolytes added to the mobile phase. 

A membrane can be either a liquid or a solid. Its electrical properties arise when it allows transport of an ion of one charge but not that of another. Membranes are usually sufficiently thick that one can distinguish an inside region and two outer boundary regions which are in contact with electrolyte solutions. Two types of membranes are considered here (1) membranes of solid and glassy materials (2) liquid membranes with dissolved ion-exchanging ions or neutral ion carriers (ionophores). In fact all of these membranes are involved in ion exchange. It is important to understand how this process affects the potentials which develop in the system at both sides of the membrane. 

Depending on the nature of the introduced electrolyte, the ion exchange can affect different regions of the EDL the diffuse and adsorption regions, and even the layer of potential-determining ions (in which case it is, however, more appropriate for one to talk about the build-up of the crystal lattice of the solid phase with the constituent ions of introduced electrolyte). The diffuse layers of counter-ions are the ones that undergo exchange most easily. 

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