Principles of Ion Exchange

All modem resins are polymeric stnictures, generally based on either a styrene or an acrylic matrix. Polystyrene Sulfonic Acid Cation Resins 

These materials are made usually by copolymerizing acrylic or methacrylic acid with DVB. The total capacity is extremely high, at 13.0 meq/dty gram, corresponding with about 6.5 meq/wet gram, or 45(X) 

Michael Streat and Francis Louis Dirk Cloete 

The basic polymer is exactly as for the polystyrene cation exchangers, but the inbodnction of die active group requires two steps. A chloromethyl group is introduced into each benzene iii%, after whidi any amine group can be introduced by a sim addition reaction with chloromethyl ether. 

A range of polyacrylic anion-exchange resins has been produced in recent yeais. The exact structure and method of manufticture have not been published, but it is clear that they contain quaternary ammonium groups (or in the case of the weakly basic materials, amino groups) attached to an acrylic skeleton. Thqr are ysically robust materials, with good operating characietistics, and are serious competitors to the polystyrene resins. 

This heterogeneous structure hes two results. First, in the case of simple, relatively small, inorganic ions, it is found that the law of mass action is not wholly obeyed, and the defined equilibrium constants mu not fixed. As an ion enters tha reain, the process becomes progressively more diflrcelt as the concentration in the resin approaches the total capecity. and the less accaseible active groups come into use. 

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Ion Exchange Chromatography - Basic principles of ion exchange chromatography and studies conducted from Texas A M University. http //ntri.tamuk.edu/fplc/ion.html. 

Owens, Dean L., Practical Principles of Ion Exchange Water Treatment, Tall Oaks Publishing, Inc., Voorhees NJ, 1985. 

Ion chromatography (IC) is a relatively new technique pioneered by Small et al.25 and which employs in a novel manner some well-established principles of ion exchange and allows electrical conductance to be used for detection and quantitative determination of ions in solution after their separation. Since electrical conductance is a property common to all ionic species in solution, a conductivity detector clearly has the potential of being a universal monitor for all ionic species. 

Investigations in aqueous systems have established many of the fundamental principles of ion exchange as well as providing useful applications. The scope of the ion exchange process has, however, been extended by the use of both organic and mixed aqueous-organic solvent systems.32,33... 

Figure 6.11 Principle of ion-exchange chromatography, in this case anion exchange chromatography. The chromatographic beads exhibit an overall positive charge. Proteins displaying a nett negative charge at the pH selected for the chromatography will bind to the beads due to electrostatic interactions...

FIGURE 6.4 Schematic illustration of the principle of ion exchange chromatography. 

A general, recent trend has been to apply the principles of ion exchange to the purification of whey or lactose solutions. Anionic and cationic exchange resins are used to remove impurities from the solution, which can then be condensed and crystallized or spray-dried directly. Ahlgren (1977) and Delaney (1976) have reviewed developments... 

Illustration of the principles of ion-exchange chromatography. See text for explanation. 

The principle of ion exchange is based on the fact that some solid materials exchange ions when in contact with a solution. The most commonly used materials are the resin ion exchangers. These have replaced most of the older aluminosilicate or hydrated oxide materials, and are available in a number of types and particle sizes. 

A rigorous mathematical treatment of ion-exchange chromatography would be rather complex and well beyond the scope of this text. A brief description of the principles of ion-exchange chromatography is given below. 

Slater MJ (1992) Principles of ion exchange technology. Butterworth and Heinemann, Oxford... 

Other consideration for selective separation are related to the basic principles of ion exchange. For example, cation displacement should proceed until the column is loaded to capacity with plutonium and americium. If this procedure is not employed, the excess resin simply sorbs the displaced cations (e.g., Mg, Na, K, Ca, etc.) and they are rejoined with the actinides during the elution cycle. 

Slater, M. J. (1991). Axial mixing and flow abnormalities. In The Principles of Ion Exchange Technology (M. J. Slater, ed.), pp. 41-49. Butterworth-Heinemann, Oxford. 

Owens D. Practical Principles of Ion Exchange. 2nd ed. Littleton, Colorado Tall Oaks Publishing 1995. 

Slater, M.J., The Principles of Ion Exchange Technology, Butterwordi, Heinemann, Boston. (1991). 

After much controversy [167], it now appears that whenever ion exchange is possible, mechanism 2 is the primary method by which an electrochemical response is observed in ZME. Much of the sensor-based research we discuss below is based on the principle of ion exchange, followed by electrochemistry. 

Pennkinetic System Skye Pharma AG, Muttenz, Switzerland The system combines CR principles of ion exchange with membrane diffusion. The system is made up of an ion-exchange polymer-drug complex as a core material, which is subsequently coated with ethylcellulose to form a water insoluble but permeable coating. Release rates are relatively constant and unaffected by variable conditions of the GI tract. The system can be formulated in capsule form as well as suspensions. Delsym (Dextromethorphan), Corsym (Chlorpheniramine) and Cold Factor 12 (Phenylpropanolamine). 

M.J. Slater, Principles of Ion Exchange Technology , Butterworth-Heinemann, Oxford, 1991. 

The principles of ion-exchange chromatography are discussed in ch. 3. Here, some useful elution systems for nucleotides are described. The descriptions are based on published work and the author s experience but it must be emphasised that variations between batches of Dowex resins may make the methods difficult to repeat and any method should be rigorously tested before use (e.g. Matthews 1968a). 

The basic principles of ion exchange have been discussed by Walton [78]. However, this discussion was mainly limited to the case of small inorganic ions. For the separation of biomolecules, e stoichiometric displacement model (SDM, next subsection) is of particular interest. This model is based on the assumption that ion exchange is the only mechanism of retention of the components studied and that the ion-exchange process can be modeled as a stoichiometric "reaction" described by the mass action principle. 

The principle of ion-exchange chromatography is not unlike that of adsorption chromatography. In the latter case, the adsorbent bears active sites which interact with molecules in their vicinity to a more or less specifically defined extent. Sample and solvent molecules compete with each other for adsorption. 

The principles of ion-exchange chromatography are well described and may be represented by the equation... 

In contrast to most separation operations, which predate recorded history, the principles of ion exchange were not known until the 1800s. Today ion exchange is a major industrial operation, largely because of its wide-scale use in water softening. Numerous other ion-exchange processes are also in use. A few of these are listed in Table 1.3. 

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