Immobilized complexing agents

Figure 14.6 Bifurcation curves in a model of the CDIMA reaction in the presence of an immobile complexing agent with c = 1.5. Solid line Hopf bifurcation curve for several values of cr steady state is stable above the curve, oscillatory state is stable below the curve. Dashed line Turing bifurcation curve homogeneous steady state is stable to inhomogeneous perturbations above, unstable below the curve. (Adapted from Lengyel and Epstein,...

Electrodes with membranes in which an ion-selective complexing agent, or ion exchanger is immobilized in a polymer matrix. They are selective for Ca2+, K+, NOj, and many other ionic species. 

High performance membranes can be made by immobilizing a liquid phase containing a complexation agent (carrier) in a thin porous support. 

By judicious choice of the membrane liquid, complexation agent and support, immobilized liquid membranes (ILM) can have both high selectivity and high permeant fluxes. Liquid membranes have the additional advantage that diffusion coefficients in liquids are several orders of magnitude larger than in polymeric membranes. Previously reported ILM research in the literature includes purification and recovery processes in both gas and liquid phases ( ). This variety of applications creates different requirements for supports for ILMs. This paper discusses criteria which influence selection of ILM support materials. 

In addition wetting agents can be conditioned in such a manner that on the one hand they possess ion exchange properties and on the other they act as complexing agents that immobilize multivalent cations that are dissolved in the aqueous phase. 

In protonic acids, where the complex anion assists ion generation, the acid may be considered as providing its own counterion, A . When such counterions are highly nucleophilic, then complex-ing agents such as metal salts or metal oxides must be used to immobilize the anions. Such complexing agents are in effect coinitiators. 

Immobilization of complexing agents on electrode surfaces was achieved by several procedures. Lane and Hubbard first demonstrated the principle by adsorbing a salicylate ligand, which could complex Fe(III) solution species, onto platinum electrodes. Cox and Majda adsorbed adenosine monophosphate onto platinum electrodes to detect Fe(II) from solution using cyclic voltammetry. Price and Baldwin used ferrocene carboxaldehyde as a model analyte to investigate a modified electrode developed to determine aldehydes and ketones. The formation... 

A series of commercial styrene-divinylbenzene copolymers called Amberlite XAD (Rohm and Haas Co., Philadelphia) has been used as a base to immobilize a variety of complexing agents (269). On XAD-2, tri-/i-octylamine (270), several ferroin-type chromogens (277), and phenylarsonic acid (272) have been used to concentrate and separate several trace species from seawater and fresh water. An EDTA ligand (273) and phenylarsonic acid on XAD-4 can also extract trace metals such as Cr(III), Pb(II), Hg(II), U(VI), Zr(IV), and Zn(II) at the sub-parts-per-billion levels, even in the presence of excess calcium and magnesium if the pH is less than 3.0. 

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