Platinum, electrode blues

The existence of materials now included among the conducting polymers has long been known. The first electrochemical syntheses and their characterization as insoluble systems took place well over a century ago. In 1862 Letheby reported the anodic oxidation of aniline in a solution of diluted sulphuric acid, and that the blue-black, shiny powder deposited on a platinum electrode was insoluble in HjO, alcohol, and other organic solvents. Further experiments, including analytical studies, led Goppelsroeder to postulate in 1876 that oligomers were formed by the oxidation of aniline. 

The amperometric dehydrogenase sensor for ethanol consists of a platinum electrode on the surface of which alcohol dehydrogenase (ADH), Meldra blue (MB) and NAD are immobilized with a conductive polypyrrole membrane as schematically illustrated in Fig.24. 

In other words, the small excess of HN02 present at the end-point can be detected visually by employing either starch-iodide paper or paste as an external indicator. Thus, the liberated iodine reacts with starch to form a blue green colour which is a very sensitive reaction. Besides, the end-point may also be accomplished electrometrically by adopting the dead-stop end-point technique, using a pair of platinum electrodes immersed in the titration liquid. 

In strongly basic solvents like HMPA, amines and liquid ammonia, solvated electrons are relatively stable. In these solvents, if the supporting electrolyte is the salt of Li+ or Na+, blue solvated electrons, esm are generated from the surface of the platinum electrode polarized at a very negative potential ... 

In 1898, Cowper-Coles 2 claimed to have successfully effected the electrolytic reduction of an acid solution of vanadium pentoxide to metallic vanadium, but the product was subsequently shown by Fischer 3 to have been a deposit of platinum hydride. Fischer, in a series of over three hundred experiments, varied the temperature, current density, cathode material, concentration, electrolyte, addition agent, and construction of cell, but in not one instance was the formation of any metallic vanadium observed. In most cases reduction ceased at the tetravalent state (blue). At temperatures above 90° C. reduction appeared to proceed to the divalent state (lavender). The use of carbon electrodes led to the trivalent state (green), but only lead electrodes produced the trivalent state at temperatures below 90° C. Platinum electrodes reduced the electrolyte to the blue vanadyl salt below 90° C. using a divided cell and temperatures above 90° C. the lavender salt was obtained. 

First tissue-based biosensor antennules from blue crabs mounted in a chamber with a platinum electrode to detect amino acids [18]... 

Platinum electrodes in conjunction with a reference electrode can be used to measure E values in environmental samples. However, these values cannot be considered definitive since they may represent a composite response of several redox couples and the actual response of the electrode can be limiting. A more direct approach is to measure the proportion of the oxidized and reduced components in a system and calculate Fh using the Nemst equation. Redox indicators [listed below with °(W)] may also be used as probes to assess redox status. Comparable to acid-base indicators, the color of these compounds changes when oxidized or reduced. With the exception of resomfin which is pink, the oxidized form of these compounds is blue while the reduced counterpart is yellow or colorless. 

Optical sensor Amperometric sensor Amperometric sensor Oxygen electrode/polysulfone membrane Platinum electrode Glassy carbon electrode/ methylene blue mediator Three separate enzyme electrodes of pH electrode/cellulose acetate membrane Platinum electrode... 

Experimental difficulties, theoretical uncertainties, and poor planning have so conspired together as to frustrate most attempts to determine the conductances or excess conductances of the electrons in amine solvents. One of the main problems in the laboratory has been the low chemical stability of the alkali metal solutions. Their blue colour gradually fades as the solutions decompose with the formation of hydrogen, a process catalysed by impurities and especially by the platinum electrodes of the cell itself. Pyrex vessels, it was recently discovered, cause sodium contamination, and for this reason much of the early research is now of doubtful worth. The experimental problems are exacerbated in the case of methylamine, whose volatility demands the use of low temperatures at which the metals dissolve but slowly. A further problem arises in the extrapolation of the data to infinitesimal ionic strength, for the appropriate conductance function to be applied depends upon the kind of species which the solution contains. And when, after all these hazards, the limiting conductance of an alkali metal solution has finally been obtained, it turns out as often as not that it can neither be compared with values for other metals because each experimenter has worked at a different temperature, nor with the conductances of normal salts because in the excitement their measurement has been overlooked. 

Fig. 28.24 A coloured atomic force micrograph of a carbon nanotube wire (shown in blue) lying over platinum electrodes (in yellow). The diameter of the carbon nanotube is 1.5 nm (1500 pm), corresponding to the wire being 10 atoms wide (rcov C = 77 pm).

The first cell (denoted with red line) contains platinum electrodes the second cell (blue line) and the third one (black line) contains steel electrodes. The first and the second cells are placed side by side in light-blocking wooden box, and the third one is inside the temperature controlled cabinet protected against electromagnetic interference of technogenic origin with aluminium sheet 1.5 mm thick. 

The cyclic voltammograms and the changes that occur to them during repetitive cycling are similar to those of 3-methylthiophene oxidation in acetonitrile. When a platinum electrode is used, the color change (red-blue) due to the redox transformation of poly (3-methylthiophene) is easily visible. A visual inspection also reveals that the electropolymerization reaction starts at the three-phase junction, as theoret-... 

Surprisingly, at first sight, redox indioators may also be used in some cases to detect the endpoint of a complexometric titration with EDTA. In fact, the endpoint of an EDTA titration may be accompanied by a ehange in the redox potential of the solution. When a mixture of Fe + and Fe + is titrated with EDTA, Fe + disappears before Fe + since Fe gives more stable eomplexes with EDTA than Fe + does. A simple inspection of Nernst s equation shows that in these conditions, the solution s redox potential decreases markedly, in particular at the equivalence point. The sharp change may be detected by potentiometry with a platinum electrode or with a redox indicator such as Variamine blue. 

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