Glass electrodes construction

The construction of these electrodes is exactly similar to that already described for the pH responsive glass electrode. They must of course be used in conjunction with a reference electrode and for this purpose a silver-silver chloride electrode is usually preferred. A double junction reference electrode is often used. The electrode response to the activity of the appropriate cation is given by the usual Nernst equation ... 

For the separation of such batteries, gel construction and microfiber glass fleece separators again compete because of the deep discharge cycles, the gel construction with its lower tendency to acid stratification and to penetration shorts has advantages for the required power peaks, microfiber glass fleece construction would be the preferred solution. The work on reduction of premature capacity loss with lead-calcium alloys has shown that considerable pressure (e.g., 1 bar) on the positive electrode is able to achieve a significantly better cycle life [31-36], Pressure on the electrodes produces counter pressure on the separators, which is not unproblematic for both separation systems. New separator developments have been presented with... 

For a review of compositional and constructional aspects of glass electrodes (especially the pH electrode), see Mattock43. 

Hydrogen electrodes can be constructed in variously shaped cells according to the purpose. An example is given in Fig. 3.7. The measurement is described in detail in practical manuals. However, for practical measurements, the glass electrode (Section 6.3) is employed. 

Indium-tin oxide (ITO) Tin-doped indium oxide, used as a thin solid film on glass when constructing optically transparent electrodes. 

The glass electrode also belongs among homogeneous membranes. For the sake of completeness, its properties will be described in chapter 6, but for construction details the reader is referred to the literature ([48]). 

Therefore, the ISE potential depends on the CO2 partial pressure with Nernstian slope. Contemporary microporous hydrophobic membranes permitted the construction of a number of gas probes, developed mainly by the Orion Research Company (for a survey see [143]. The most important among these sensors is the ammonia electrode, in which ammonia diffusing through the membrane affects the pH at a glass electrode. Other electrodes based on similar principles respond to SO2, HCN, H2S (with an internal S ISE), etc. The ammonia probe has a better detection limit than the ammonium ion ISE based on the non-actin ionophore. The response time of gas probes depends mostly on the rate of diffusion of the test gas through the microporous medium [77,143]. 

The dye-sensitised solar cell (DSSC) is constructed as a sandwich of two conducting glass electrodes filled with a redox electrolyte. One of the electrodes is coated, using a colloidal preparation of monodispersed TiOj particles, to a depth of a few microns. The layer is heat treated to rednce resistivity and then soaked in a solution of the dye until a monomolecnlar dispersion of the dye on the TiO is obtained. The dye-coated electrode (photoanode) is then placed next to a connter electrode covered with a conducting oxide layer that has been platinised , in order to catalyse the reduction of the mediator. The gap between the two electrodes is filled with an electrolyte containing the mediator, an iodide/triodide conple in acetonitrile. The structure is shown schematically in Fignre 4.29. 

Procedure 3 We construct cell (V) using the HA type acid under study and its conjugate base and measure the emfs by varying the ratio Ca/Cs. The procedure to vary the ratio Cs/Ca can be replaced by the titration of the acid HA with a strong base (BiuNOH in MeOH, toluene-MeOH, or 2-PrOH), but the alcohol introduced with the base may have some influence on the results. Because the glass electrode has been calibrated in Procedure 2, the emf values can be converted to pH values. 

Procedure 1 Cell (VI) is constructed using a univalent cation-sensitive glass electrode (Ag electrode for Ag+) and the emf is measured by titrating metal ion M+ with ligand L ... 

In constructing an electric cell for potentiometric titrations it is necessary, of course, to use a second electrode to complete the circuit, in addition to the measuring electrodes (commonly called indicator electrodes ) described above. Ideally the second electrode would be a hydrogen electrode which (as explained in the entry on electrode potential) is the standard reference electrode for which die potential, in equilibrium with its ions, is defined as zero. Since it is awkward to use, other electrodes of known potential, such as the calomel electrode or the glass electrode, are commonly used as reference electrodes. The arrangement of the apparatus is as shown in Fig. 1. 

Figure 9.8 Experimental arrangement for use of thin-layer electrode constructed with glass or quartz plates. W, Working electrode R, reference electrode A, auxiliary electrode a, inert-gas inlet.

In addition, other sources of errors can occur owing to imperfections in the glass-membrane construction or due to limitations related to the reference electrodes and the diaphragm. Temperature also plays an important role in pH measurement. However, for these sources of errors reference is made to the literature for more detailed information15. 

Two hypotheses have been proposed (Eisenman, 1962 Mullins, 1975) to account for the high Na+/K+ selectivity in Na+ dependent transport systems. Mullins emphasizes a geometrical fit of the cation. Eisenman emphasizes the electrical field strength of the putative binding sites. Many of the predictions made by Eisenman have been borne out experimentally in the ion-coupled systems and are complemented by the construction of ion-specific glass electrodes (Eisenman, 1962). 

Brown and his colleagues constructed an apparatus in which a solution traveled the length of an artificially contrived crack. The solution was made to wet a filter paper and its pH was measured by means of a glass electrode with a long, thin, tip. 

Fig. 12. Schematic design of a redox electrode. It strongly resembles the pH glass electrode. The active measuring element is a noble metal, usually constructed as a ring around the tip of the electrode...

The coupling of biomimetic dynamic interfaces with electrochemical impedance spectroscopy has shown value in the study of ion transport studies across tethered bilayers [56]. Electrochemical impedance spectroscopy may prove valuable used in conjunction with the previously described techniques [57, 58]. Again electrode construction with readily chemically adaptable surface materials such as gold, silver and glass/silica amongst others make this a promising approach for introducing functional interfaces. 

Many designs of calomel electrodes exist, and several types are commercially available. Some of these are constructed for voltammetric work, whereas others are used in connection with glass electrodes. The latter type generally has a high resistance, which must be considered when the choice of voltmeter or potentiostat is made. 

The solution is poured into the electrochemical cell. This cell is flat bottomed and cylindrical in construction and has a gas inlet and two side-arms with female Quickfit joints into which are inserted two male joints terminated with sintered-glass frits. The conducting-glass electrode is then attached to a crocodile clip with a long wire contact, which is clipped so that the crocodile clip is above the surface of the liquid. The graphite rod and SCE are then placed in the side-arms provided (separated from the solution by a sintered-glass frit). 

Fig. 75. Construction of a sterilizable enzyme electrode for the determination of penicillin. A flat glass electrode, B reaction chamber containing enzyme, C dialysis membrane, D holder. (Redrawn from Enfors, 1987).

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