Flow-through electrode

TABLE 3-4 The Limiting-Current Response of Various Flow-Through Electrodes... 

The limiting-current method has been used widely for studies in packed and fluidized beds (see Table VII, Part H). Limiting current measurements in these systems overlap in part with the design and analysis of packed-bed and fluidized-bed electrochemical reactors in particular the potential distribution in, and the effectiveness of, such reactors (for example, for metal removal from waste streams) is an extensive area of research, which cannot be covered in this review. For a complete discussion of porous flow-through electrodes the reader is referred to Newman and Tiedemann (N8d). 

Porous flow-through electrode design (coulometric or amperometric). 

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.

A flow-through electrode has also been constructed for the determination of cyanide [282]. In some media it is preferable to first separate cyanide by distil-... 

The various versions of the Cu ISE also include flow-through electrodes [36, 389], porous flow-through electrodes [290] and flow-through microelectrodes [407]. 

Figure 4.15 — (A) Tubular flow-through electrode 1 Perspex body 2 conducting epoxy cylinder 3 mobile carrier PVC membrane 4 electric cable 5 channel (1.2 mm ID) 6 holders 7 screws 8 0-rings. (B) Schematic diagram of a system for on-line monitoring of ammonia ISE tubular flow-through ammonium ion-selective electrode R reference electrode W waste. (Reproduced from [137] with permission of the Royal Society of Chemistry).

An electrochemical cell should not be confused with a biological cell, which is the basic unit of life. Electrochemical cells contain chemical solutions and electrodes to conduct electrons. As shown in the figure on page 136, both oxidation and reduction reactions occur in the cell, but these reactions are separated. Separation is essential so that electrons can flow through electrodes and into attached wires, which can be routed to wherever electricity is needed. To maintain electrical balance at the electrodes—in other words, to complete the circuit so that electricity flows in a loop—an electrolyte allows the flow of ions between the two halves of the system. This cell produces electricity and is called a voltaic cell. The reaction proceeds as long as the materials last. 

One still has to transform the current densities into the currents. This is done by recalling that the total current 7j (not current density ) flowing through electrode 1 is equal to the current I2 through electrode 2, i.e.,... 

By introducing Mg2"1" selective membrane, placed in a flow-through electrode body, into the Microlyte 6 electrolyte analyzer (instead of... 

Flow electrodes. Rather than move the electrode past the solution, the sample solution can be flowed past a stationary electrode. The tubular platinum electrode (Figure 5.34) and the gold micromesh flow-through electrode (Figure 5.35) are both ingenious attempts to produce electrodes that are useful for the measurement of electroactive materials in a continuously flowing stream. Ap-... 

Figure 5.35 Gold micromesh flow-through electrode (a) cell system (b) detail of gold micromesh screen.

It is also possible to employ detectors with solutions flowing over a static mercury drop electrode or a carbon fiber microelectrode, or to use flow-through electrodes, with the electrode simply an open tube or porous matrix. The latter can offer complete electrolysis, namely, coulometric detection. The extremely small dimensions of ultramicroelectrodes (discussed in Section 4.5.4) offer the advantages of flow-rate independence (and hence a low noise level) and operation in nonconductive mobile phases (such as those of normal-phase chromatography or supercritical fluid chromatography). 

Flow-through electrodes -> flow cell, and - hydrodynamic electrodes... 

R.E. Soida, Flow-through Electrodes Composed of Parallel Screens, Electrochimica Acta, 22, pp. 439-43 (1977). 

In the first step, when the electrodes are in the upper position, the current I is applied through the electrodes a and b, while the voltage V across the electrodes c and d is measured. Then the electrode function is switched by 90 thus the current J2 flows through electrodes b and c and voltage V2 is read from electrodes d and a. From the values... 

Selectivity enhancement in porous electrocatalysts deserves serious consideration in process design, despite increased surface-area requirements. In Eqs. (126) and (127), the potential was assumed constant within the thin porous electrode. With thick flow-by and flow-through electrodes, potential variation and slow transport in the pores could improve specificity, depending on the transfer coefficients of the parallel steps. 

In packed-bed, flow-through electrodes, concentration and potential variation within the bed can also give more than one steady state. The convective transport equation with axial dispersion, coupled with Ohm s law for the electrode potential, was solved recently (418) by polynomial expansion and orthogonal collocation within the bed, to determine multiplicity regions. 

Fig, 80. FIA manifold comprising a glucoamylase (GA) reactor and a GOD flow-through electrode for measurement of maltose and starch. (Redrawn from Scheller et al., 1987c). 

Johnson et al. [81] have developed a pulsed anodic technique at platinum flow-through electrodes and have applied it successfully to the detection of a number of classes of molecules such as alcohols and carbohydrates, amines, and sulphur compounds. The method has also been extended to the detection of analytes at potentials where they are not electroactive. This procedure has been used to detect Cl" and CN [82, 83]. 

One of the advantages of flow-through electrodes over other types of hydrodynamic electrodes is that they involve no moving parts. They are therefore ideal for use in conjunction with both spectroscopic and microscopic techniques. Whilst both channel and tubular electrodes can be used in... 

A. N. Strohl and D. J. Curran, Flow Injection Analysis with Reticulated Vitreous Carbon Flow-Through Electrodes. Anal. Chem., 51 (1979) 1045. 

J. Wang and H. Dewald, A Porous-Jet Flow-Through Electrode. Talanta, 29 (1982) 453. 

Figuerola et al.[37] determined free cyanide and cyanide present in weak complexes sequentially using two silver iodide/silver sulfide electrodes with an intervening gas> diffusion separator. Following the potentiometric determination of free cyanide with the first flow-through electrode, the effluent was acidified, and the evolved hydrogen cyanide from weakly complexed species w as transferred through the membrane of the gas-diffusion separator, collected in an alkaline acceptor stream and determined with the second electrode. 

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