Liquid-ion exchanger systems

Membrane Liquid ion-exchanger system Lower limit of detection ... 

Organophosphoric acids and a variety of organophosphorus mediators have been examined as liquid ion-exchanger systems for PVC uranyl ISEs (63,64) (Table 3.17). The sensors are readily made by multiple-stage extractions from... 

In liquid ion-exchanger systems it is clear that the solvent (often called mediator) plays an important part in controlling selectivity. To introduce a phosphonate mediator into oior CBS electrodes it was necessary to avoid the need for a hydrolysis stage (step ii). This was achieved by covalently-binding diallyl-phosphoric acid (DAPH) into the membrane. These new CBS electrodes exhibited similar electrochemical responses to the triallyl phosphate system (TAP), showed excellent precision, and had long lifetimes. ... 

Other studies, in agreement with our data, have shown that PVC-membranes are permeable to calcium ions and linear Mackay plots are obtained, which indicate that a liquid ion-exchanger process is taking place. The CBS membrane containing only sensor (no mediator) is impermeable to Ca " " and gave a curved Mackay plot which is behaviour typical of a solid ion-exchanger. When a mediator is present (DOPP) the behaviour becomes more like a liquid ion-exchanger system. 

Ross and Frant [128] describe an exchanger phase based on a substituted thiogly-colic acid R - S — CH2 — COO", which reacts selectively with Cu and Pb ions. Since the introduction of solid-state electrodes for these two ions, the development of liquid ion-exchanger systems for each individual ion has not been pursued. 

Ion-selective electrodes are membrane systems used as potentiometric sensors for various ions. In contrast to ion-exchanger membranes, they contain a compact (homogeneous or heterogeneous) membrane with either fixed (solid or glassy) or mobile (liquid) ion-exchanger sites. 

Fig. 5.6. A flow-through electrode system for liquid-membrane ISEs [111] 1 - reference electrode 2 - hole through which the sample solution flows 3 - liquid ion-exchanger reservoir, 4 - triangular piece of a frit soaked with the liquid ion-exchanger.

T0521 Met-Tech, Inc., Metal Separation by Liquid Ion Exchange T0525 Microbial Aquatic Treatment Systems, Inc. (MATS), Biomats T0536 Molten Salt Oxidation—General... 

Figure 1 shows several types of mass transfer or diffusion cells, which are of the simplest design for performing bulk liquid membrane (BLM) processes. Each of the devices is divided into two parts a common part containing the membrane liquid, M and a second part in which the donor solution F and acceptor solution R are separated by a solid impermeable barrier. The liquid, M contacts with the two other liquids and affects the transfer between them. All three liquids are stirred with an appropriate intensity avoiding mixing of the donor and acceptor solutions. For a liquid-ion exchange in a BLM system. Fig. 2 shows the transfer mechanism of cephalosporin anions, P , from donor (F) to acceptor (R) solution... 

The following models have been mainly used in liquid-phase adsorption and biosorption and, in some cases, for ion-exchange systems with inorganic ion exchangers (Rengaraj et al., 2004 Bektas and Kara, 2004). 

Waste Treatment. Environmental concerns have increased the need to treat liquid discharges from all types of industrial processes, as well as runoffs where toxic substances appear as a result of leaks or following solubilization (see Wastes, industrial). One method of treatment consists of an ion-exchange system to remove the objectionable components only. Another involves complete or partial elimination of liquid discharges by recycling streams within the plant. This method is unacceptable unless a cyclic increase in the impurities is eliminated by removing all constituents prior to recycling. 

In a series of studies we recently demonstrated (29, 30, 63-67) that the resolution of peptides on reversed phase can be profoundly influenced by the addition of appropriate counterionic reagents to a mobile phase of deflned pH, ionic strength, and water content. Retention under these conditions can be discussed in terms of ion-air associations between the ionized peptide and a counterion in the mobile phase and subsequent sorption of the complex onto the stationary phase. Alternatively, adsorption of the counterion, particularly if it is lipophilic, onto the nonpolar stationary phase may occur, and peptide retention would then be mediated by dynamic liquid-liquid ion-exchange effects. Arguments in favor of the participation of one, the other, or both of these alternative pairing-ion phenomena in ion-pair chromatography have been extensively reviewed (16, 28b, 62, 68, 68a). It can be shown (62, 68) that retention behavior in ion-pair systems can be described by... 

The application of solvent extraction to metallurgical systems is classified into two groups based on the nature of the extractable species involved. The first group involves an ion-pair transfer mechanism and the second group is the liquid ion-exchange mechanism, which is essentially the interchange of anions or cations between the aqueous and organic phase. 

There are two important types of liquid membranes used in analytical applications. One type involves an ion-exchanging system dissolved in a hydrophobic solvent, usually of low permittivity. The other type makes use of an ionophore or neutral complexing agent dissolved in a similar solvent. In both systems, Donnan potentials are established on either side of the membrane but a diffusion potential is absent because of the mobility of the solute in the liquid phase. More details about the functioning of these membranes are given in this section. 

Commercial ISEs are made with liquid membranes involving both ion-exchanging systems and ionophores (see table 9.7). The solvent used is a hydrophobic liquid with a low relative permittivity. Examples include decane-l-ol, 5-phenyl pen tan-2-01, octyl phtalate, tri-n-phenyl phosphate, and 2-nitro-/ -cymene. Another important property of the solvent is that it have a low vapor pressure so that it is not... 

There are five modelsl l which can be used to represent the kinetics in ion exchange systems which involve liquid exchange phase mass transfer, solid phase mass transfer, and chemical reaction at the exchange group. 

---