Solid state membrane electrodes

Insertion of Eqs. (18) in (15) results in an Equation for a dissolving solid state membrane electrode in the absence of complexing agents. In case aA = aB = 0 (e.g., pure H20) the stationary potential can be expressed as ... 

Gel of collodion, PVC, etc. Solution (with low ) of ion exchangers or complex in suitable solvent (apparently dry) "solid-state membrane electrode K, nh , Ca bf4, no3... 

Solid-state membrane electrodes. All members of this class are direct working. 

Walters [24] examined the effect of chloride on the use of bromide and iodide solid state membrane electrodes, and he calculated selectivity constants. Multiple linear regression analysis was used to determine the concentrations of bromide, fluorine, and iodide in geothermal brines, and indicated high interferences at high salt concentrations. The standard curve method was preferred to the multiple standard addition method because of ... 

They are classified by membrane material into glass membrane electrodes, crystalline (or solid-state) membrane electrodes, and liquid membrane electrodes. Liquid membrane electrodes are further classified into liquid ion-exchange membrane electrodes and neutral carrier-based liquid membrane electrodes. Some examples are shown in Fig. 5.36 and Table 5.3. If the membrane is sensitive to ion i of charge Z and the activities of i in the sample and internal solutions are equal to (i) and a2(i), respectively, the membrane potential, m, which is developed across the membrane, is... 

Considerable work has been devoted to the development of solid membranes that are selective primarily to anions. The solid-state membrane can be made of single crystals, polycrystalline pellets, or mixed crystals. The resulting solid-state membrane electrodes have found use in a great number of analytical applications. 

The sensitivity of ion-selective electrodes can be excellent in metal-ion-buffered solutions, that is, at fairly high total metal-ion concentrations. Under these conditions, commercial solid-state membrane electrodes were shown to follow the Nemst equation in fresh waters down to pCu 11-12 and after preconditioning in a metal-ion buffer to pCu = 13 (Sigg and Xue, 1994 Sunda and Hanson, 1979 Xue and Sigg, 1990). Some ion-selective electrodes, especially the Cu electrode, show interference in high chloride media (seawater). 

Single crystal and solid-state membrane electrodes... 

Without in any way negating the wide-ranging utility of glass membrane electrodes for pH, pNa and pNH measurements and the good solid-state membrane electrodes for fluoride, sulphide and other ions, the main focus of development work of the last twenty years has been in the search for better liquid membrane systems. This has been stimulated by the convenience of PVC matrices for trapping and supporting liquid membranes (32-34,83). 

The length of time over which a chemical sensor can be expected to function reliably can be remarkably great (in the range of years), as in the case of glass-membrane or solid-state membrane electrodes, the lambda probe (Section 28.2.2.3), and the Taguchi gas sensor (see Section 28.2.2.2). On the other hand, a biosensor that depends upon a cascade of enzymes to... 

MT = Membrane type G = Glass-membrane electrode P = PVC-membrane electrode S = Solid-state membrane electrode ... 

At low analyte concentrations, the activity of interfering ions must be considered. Ion-selective electrodes can be divided into categories based on the nature of the membrane material. These categories include glass membrane electrodes, liquid membrane electrodes, and solid-state membrane electrodes. 

Solid-state membrane electrodes include H+, F , CN , Cl , 1, Br, H2S, CN , thiourea, Pb, Cu, and Cd selective electrodes. In this category, silver halide and silver sulphide electrodes are found. The macroscopic ion-selective electrodes made with these systems have been applied in many fields, such as medicine, food industry, and environmental studies (56, pp. 93,96,103,104) but their full potential has not yet been exploited in terms of SECM studies. 

In a few cases (for example with some solid-state membrane electrodes) it is possible to keep unpolarizable the inner contact point to the ion meter, where the crossover from ion conduction to electron conduction occurs (reversible redox reaction). Such solid-state contacts eliminate the need for inner solutions with constant ion activities, and are thus practically maintenance-free. To be sure, with constructions of this type one must keep in mind that there is no longer a compensating inner reference electrode. The temperature dependence of a cell containing such an electrode may be entirely different from that of a symmetric cell in addition, the polarizability can be larger. There is much freedom possible in the design of individual electrode shapes (see Fig. 21). 

More recent investigations of C. Harzdorf [84] have shown that thick layers electrolytically deposited on silver (for example anodized for one hour at 1 mA/cm in 1 M KQ, KBr, 0.1 M K1 solution and finally clearly polished with a soft rag) are completely equivalent to the homogeneous solid-state membrane electrodes. 

S Preparation of Solid-State Membrane Electrodes Based on AgaS... 

To improve the response time, the surface of the solid-state membrane electrode can be polished to a luster with diamond paste or moist AI2O3 of particle size < 0.1 m-Poisoned electrodes can usually be restored by sanding and repolishing the surface. 

Electrode manufacturers add the appropriate silver halide to the Ag2S support matrix in finely divided form and offer electrodes with these AgHal-Ag2S mixed pellets as halide solid-state membrane electrodes. 

There have been many attempts to develop selective precipitate membrane electrodes for the important sulfate and phosphate anions. Unfortunately they have all failed to date. A sulfate-sensitive solid-state membrane electrode with a pellet of 31.7% Ag2S, 31.7% PbS, 31.7% PbS04 and 5% CU2S has been described [91], but its selectivity over I, HPO4" and SO3 is low. 

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