Electrodes continued

If metallic electrodes were the only useful class of indicator electrodes, potentiometry would be of limited applicability. The discovery, in 1906, that a thin glass membrane develops a potential, called a membrane potential, when opposite sides of the membrane are in contact with solutions of different pH led to the eventual development of a whole new class of indicator electrodes called ion-selective electrodes (ISEs). following the discovery of the glass pH electrode, ion-selective electrodes have been developed for a wide range of ions. Membrane electrodes also have been developed that respond to the concentration of molecular analytes by using a chemical reaction to generate an ion that can be monitored with an ion-selective electrode. The development of new membrane electrodes continues to be an active area of research. 

Electrodes - continued glass, 555, 557 glassy carbon, 613 graphite, 613... 

The mechanism of the iodide formation at platinum immersed in aqueous electrode was recently studied by laser-activated voltammetry in a channel flow cell system [161]. In this technique, solid deposits of iodine are removed from the electrode continuously by short nanosecond high-power laser pulses. By removing deposits on electrode surfaces within a channel flow cell, the voltammetric measurements becomes time independent and data can be analyzed and modeled quantitatively. Laser activation using a 10-Hz pulsed Nd YAG 532-nm laser was shown to remove bulk iodine from the electrode surface so that under sustained pulsed... 

A number of other carbon materials have been used for electrochemical detection [6] however, at this point none of these appear to have a clear advantage over the electrodes described earlier. Nevertheless, these alternative materials certainly do work and there is little doubt that we will continue to see additional entries as the search for the ideal electrode continues. The chapter on carbon electrodes by McCreery and Kneten (Chap. 10) is a good place to review the fundamental issues. 

The stability of the solid-state Ca(II)-ISE was evaluated by immersing the electrode continuously in pulp filtrate for 9 days. The electrode was removed from the pulp filtrate only to make a three-point calibration once per day. The slope was found to be stable (27 +1 mV/decade) for the whole duration of the test (9 days), and the drift of the standard potential was ca. 1 mV/day. 

The solution of models of these electrodes continues to be achieved using methods such as finite difference, finite elements, finite volume, shooting etc.6,7 Here, we present an alternative approach and make comparisons with solutions of models using alternative numerical methods. 

Because any potentiometric electrode system ultimately must have a redox couple (or an ion-exchange process in the case of membrane electrodes) for a meaningful response, the most common form of potentiometric electrode systems involves oxidation-reduction processes. Hence, to monitor the activity of ferric ion [iron(III)], an excess of ferrous iron [iron(II)] is added such that the concentration of this species remains constant to give a direct Nemstian response for the activity of iron(III). For such redox couples the most common electrode system has been the platinum electrode. This tradition has come about primarily because of the historic belief that the platinum electrode is totally inert and involves only the pure metal as a surface. However, during the past decade it has become evident that platinum electrodes are not as inert as long believed and that their potentiometric response is frequently dependent on the history of the surface and the extent of its activation. The evidence is convincing that platinum electrodes, and in all probability all metal electrodes, are covered with an oxide film that changes its characteristics with time. Nonetheless, the platinum electrode continues to enjoy wide popularity as an inert indicator of redox reactions and of the activities of the ions involved in such reactions. 

Fig. 5.39. I/V plot of a typical MDMO PPV/PCBM bulk heterojunction solar cell with a Au electrode (continuous line) and an LiF/Au electrode (dotted line), respectively, in the dark and under illumination...

As the potential approaches , [A] =o decreases even further. Thus, the flux of A to the electrode continues to increase, causing the current to rise. However, eventually [A],t=o reaches zero and the flux of A cannot change any further. Under the conditions of the CV experiment, once [A] =o = 0 the Nernst diffusion layer (the distance from the electrode at which concentration changes in A are associated solely with the electrolysis mechanism and the resulting diffusion is the only form of mass transport) begins to relax further into the solution as the diffusion process tries to equalize the concentrations of A and B... 

Three of the 52 electrodes placed for lower extremity stimulation experienced changes in the responses of the muscles. One of these was due to a disconnection at the connector site between the implant and the electrode lead. This was repaired and the electrode continued to function without further problems. The remaining two electrodes (biceps femoris and tibial nerve) were not replaced, as they did not impact function for the subjects involved. 

The interest in nanopatterned electrodes continues to stimulate activity, especially with the desire to prepare one-dimensional (ID) or two-dimensional (2D) structures (Section 18.3.4), this being associated sometimes to applications in the field of sensors. 

The development of potentiometric detectors based on ion-selective electrodes continues to expand the scope of clinical and pharmaceutical applications of FIA. The small surface area of the sensor avoids adsorption problems and extends the service life of the electrode. The surface can be readily renewed periodically by alternating the washing cycles with the sampling cycles. The selectivity thus achieved is usually very good as it relies on differences in the... 

Voltammetry with membrane electrode Continuous Au cathode, 0.1 mol I- HCIO4 membrane, Pt, Ag/ AgCI n.a. 33 1 (pulse mode) n.a. Sensor-like measurements in situ for process control... 

Fig. 9.42 Complex plane plot of porous electrode continuous line analytical solution, triangles numerical solution inset high-frequency part of plot (impedances are in f2) (From Ref [455]. Reproduced with permission of Electrochemical Society)...

As applications in the use of oxygen electrodes continue to multiply, design modifications and adaptations of existing apparatus can be expected to keep pace. 

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