Liquid ion exchange and

Eisenman, Theory of membrane electrode potentials an examination of the parameters determining the selectivity of solid and liquid ion exchangers and of neutral sequestering molecules. Chapter 1 of Ion-Selective Electrodes (ed. R A Durst), National Bureau of Standards, Washington (1969). 

There are two kinds of ionophores charged ones, which are called liquid ion exchangers, and neutral carriers. Because they are mobile in both the free and in the complexed form, mobilities of all species are again part of the selectivity coefficient together with the ion-exchange equilibrium constant. The best-known neutral ionophore is valinomycin (Fig. 6.15a) which shows a 1,000 1 selectivity for K+ in preference to Na+ and no pH dependence. In its uncomplexed form, it is electrically neutral. A better-known representative is di(n-octyl phenyl) phosphonate (Fig. 6.15c), which shows good selectivity for calcium ion and is relatively pH insensitive. 

Today, two industrial methods are applied to meet this target solvent extraction (liquid ion exchange) and ion exchange by resins. Plants using the latter process can be found exclusively in China (smaller works). All others are equipped with liquid ion exchange facilities. 

Varoqui R, Pefferkorn E. Selective liquid-liquid ion-exchange and structural properties of amphiphilic polyelectrolytes in organic media. J Phys Chem 1975 79 169-180. 

K. L. Power. Operation of the First Commercial Copper Liquid Ion Exchange and Electlowinning... 

As an alternative to the use of a porous disk as a rigid supporting medium, it is possible to immobilize liquid exchangers in tough I VC membranes. In this type of electrode, the liquid ion exchanger and PVC are dissolved in a solvent such as tetrahydrofuran. The soivcnl is evaporated to leave behind a flexible membrane lhal can be cut. shaped, and bonded to the end of a glass or plastic tube. Membranes formed in this way behave in much the same way is those in which the ion exchanger is encased as a ljt uid in the pores of a disk. Most liquid-membrane electrodes arc of this newer type. 

In the present work measurements were made of molar conductivity versus concentration of several electrolytes dissolved in a mixed liquid ion exchanger and a diluent of low polarity. 

An interesting approach to miniature electrodes is the coating of a fine platinum wire with a mixture of a liquid ion-exchanger and poly(vinyl chloride) or poly(methyl methacrylate) [14]. Although the mechanism by which these electrodes function is not known (there is no internal reference electrode), they do appear to function almost as well as the larger commercial varieties. 

Liquid ion-exchange and tracer ( In) studies have been made of the hydrolysis of In in acidic solution. ... 

Liquid-membrane electrodes include classical ion-exchange, liquid ion-exchange, and electroneutral ionophore-based liquid monbrane electrodes. Of particular interest are systems where the ion-exchanging compounds are dissolved macrocyclic compounds that have a strong selectivity to alkali metals. The stability of the formed complexes in nonpolar solvents far exceeds that found in water and allows for the fabrication of membrane-free micropipettes where the nonpolar/water interface is the membrane. Unfortunately, this leads to higher resistance than that exhibited by crystalline micropipettes and requires the addition of lipophilic salt to the nonpolar solvent to decrease the pipette resistance. 

The ion-selective electrodes (ISEs) provide rapid and selective potentiometric techniques for the determination of metals in water samples. Three categories of ISEs can be mentioned (a) solid state, (b) liquid ion exchangers, and (c) neutral carriers. 

The preparation procedure of iron zeolites strongly influences the nature and distribution of iron species in the catalyst and the catalytic performance. Catalysts were prepared by hydrothermal synthesis, liquid-ion exchange, and chemical vapor deposition containing molar Fe/Al ratios in the range of 0.26-1. Activation in steam of the isomorphously substituted iron zeolite leads to superior propylene yields (22-25%) as compared to iron zeolites prepared by liquid-ion exchange and chemical vapor deposition (9-16%), with propylene selectivities around 40%. Iron impurities (170 ppm Fe) in steamed commercial H-ZSM-5 induce relatively low conversions of propene and N2O, but lead to a propylene selectivity of 90%. Mononuclear Fe sites are crucial for ODHP as iron species in large clusters enhance deep oxidation. ... 

To date in vivo blood flow measurements of various ions have only been carried out sporadically. This is due to the problems associated with this type of measurement. Since ion-selective electrodes can usually tolerate temperatures only as high as about 50°C or just slightly above 100°C, the necessary sterilization is not so simple. With the newer liquid ion-exchanger and ion-carrier electrodes, too little is known about the toxicity properties of the active phases. The blood-compatible glass membrane electrodes often collect albumin deposits on the electrode surface during flow measurements, which increase with time and cause the electrode potential to drift. Sometimes blood clots will also form, which are perilous to the research subject. 

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