Specific ion exchangers

Removal of ultraviolet absorbing organics by passage through a specific ion exchange resin such as Amberlite XAD-2. 

Construction AND Structure of Metal-Organic Frameworks with Specific Ion-Exchange Property... 

The basic difference between adsorption and ion exchange is that while there is only one isotherm at a specified temperature for adsorption, more than one isotherm can exist at a specified temperature for different normalities of the solution in the exchange of ions of different valences due to the concentration-valence effect (Helfferich, 1962). Thus, a specific ion-exchange system presents one equilibrium curve (isotherm) only under constant temperature and normality. This is why, while the term isotherms" is used for the equilibrium curves in the case of adsorption, the term isothemi-isonormal should be used for ion exchange. 

Shrinking core model The shrinking core model has been derived for noncatalytic solid-fluid reactions (Levenspiel, 1972). However, it has been successfully used for specific ion-exchange systems—those using synthetic ion exchangers, mainly chelating resins (Cortina et al, 1998 Juang, 1999). 

Metal specific ion-exchange resins bearing hydroxyoxime groups have been prepared [10] from substituted phenylacrylates (Fig. 6). 

Bibler, J. P., Wallace, R. M., and Bray, L. A. Testing a New Cesium-Specific Ion Exchange Resin for Decontamination of Alkaline High-Activity Waste, Report WSRC-RP-89, Westinghouse Savannah River Co., Aiken, SC, 1989. 

Other new sensory membranes are being developed for use with neutral molecules, but despite the time and effort spent on developing specific ion exchange membranes, they have so far found only limited application in clinical chemistry. Liquid ion exchangers are more promising and as well as being extremely versatile are said to be easier to manipulate. Their future role will depend on improvements in their selectivity (R14). 

Figure 2.2 An example of a specific ion exchange resin and its relation to an analytical...

Table 2.1 Matrix, functional group, and ion affnities of some common specific ion exchangers...

Di Giacomo, H. J. 1976. Non-specific ion exchange of Zn and Ca in a Ca-montmorillonite. MS thesis. The Pennsylvania State University, Univereity Park, PA. 8lpp. 

To perform a separation, the eluent is first pumped through the system until equilibrium is reached, as evidenced by a stable baseline. The time needed for equilibrium to be reached may vary from a couple of minutes to an hour or longer, depending on the type of resin and eluent that is used. During this step the ion-exchange sites will be converted to the E form Resin-N Rs E". There may also be a second equilibrium in which some E is adsorbed on the resin surface but not at specific ion-exchange sites. In such cases the adsorption is likely to occur as an ion pair, such as E Na or E-H+. 

These chelating resins have found most of their use in metal ion recovery processes in the chemical and waste recovery industries. They may find use in fermentation applications where the cultured organism requires the use of metal ion cofactors. Specific ion exchange resins have also been used in laboratory applications that may find eventual use in biotechnology product recovery applications. 

The effect of additives. Here the aim was to attempt to trap out any reactive boron species that may have been causing the product instability. The addition of various aldehydes, or dienes, boron specific ion exchange resins or other boron trapping agents just before work-up had no effect on the product stability. 

Recent laboratory studies and field operations have demonstrated the excellent performance of a macroreticular boron-specific ion-exchange resin, Amberlite XE-243, for deborat-ing several process streams, sea water, and irrigation water. One large plant is now operating successfully on sea water. Further studies on this product are currently in progress in several areas throughout the world. 

The detection of the current generated by reaction at the surface of (usually) carbon fiber or copper microelectrodes at a fixed voltage is capable of low detection limits for electroactive compounds using amperometry, Table 8.14. Several approaches that allow the full possibilities of multiple electrode and pulsed amperometric detection (established techniques in liquid chromatography (section 5.7.4)) have been proven for capillary electrophoresis [508,511]. These methods are not widely used, possibly due to a lack of commercial products and support. Potentiometric detection with polymer-coated wire microelectrodes containing relatively non-specific ion exchange ionophores was used for the detection of low-mass anions or cations [510,511]. 

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