Ferricyanide/ferrocyanide

Fleischmann M., Graves P.R., Robinson J., The Raman-spectroscopy of the ferricyanide ferrocyanide system at gold, beta-palladium hydride and platinum-electrodes, J. Electroanal. Chem. 1985 182 87-98. 

Formation of Red-Brown Product in Ferricyanide/Ferrocyanide Reaction... 

Principle The ferricyanide/ferrocyanide reaction is known as reaction Kamovsky-Roots (Karnovsky and Roots, 1964). A final product of this... 

In redox electrodes an inert metal conductor acts as a source or sink for electrons. The components of the half-reaction are the two oxidation states of a constituent of the electrolytic phase. Examples of this type of system include the ferric/ferrous electrode where the active components are cations, the ferricyanide/ferrocyanide electrode where they are anionic complexes, the hydrogen electrode, the chlorine electrode, etc. In the gaseous electrodes equilibrium exists between electrons in the metal, ions in solution and dissolved gas molecules. For the half-reaction... 

The Surface Potential arising from the Interaction between the Surface "States" and the Redox Couples in the Solution. When the ferricyanide/ferrocyanide redox couple is present in a 0.1 N NaOH solution, the dark cathodic current of the n-GaP (111)-face sets out at —1.1 V (SCE), showing that an electron transfer occurs... 

Figure 8. U, values for the (lll)-face of n-GaP (dark) at various concentrations of the ferricyanide/ferrocyanide couple (equal concentrations) (9) 0M (O) 0.005M (A) 0.05M (A) 0.4M E(Ox/R) redox potential of the redox couple determined by the cyclic voltammetry (ij/) the Us for a p-GaP in the absence of...

There are several salts that behave in this way at atmospheric temperatures, the more important being ammonium acetate potassium bromate, carbonate, cyanide, ferricyanide, ferrocyanide, iodate, and permanganate disodium hydrogen phosphate and sodium borate and carbonate.4 In the case of potassium chlorate the points L and S appear to be practically coincident, whilst for the majority of salts the point S lies somewhere to the left of L, namely at S —that is to say, saturation occurs before the limiting concentration is reached. Generally speaking, at the ordinary temperature, concentrated solutions of salts are less corrosive than distilled water—that is, the point S lies below the level of A, exceptions being 5 ammonium sulphate, aluminium... 

Blaedel, W.J. Schieffer, G.W. A hydrodynamic voltammetric study of the ferricyanide/ferrocyanide system with convective electrodes of platinum, gold, glassy carbon, carbon film, and boron carbide. J. Electroanal. Chem. Inter. Electrochem. 1977, 80, 259-271. 

It is, however, to be pointed out that this simplified picture constitutes at the utmost a rough approximation to the real situation. In fact, a close examination of reorganization energies, derived from different series of experimental data shows large differences between X values of various ions and even between those concerning the same ionic species. Thus, for instance, the values of X mentioned in the literature for the ferricyanide/ferrocyanide redox couple vary from 0.4 to about 1.2... 

Du J, Li Y, Lu J. Flow injection chemiluminescence determination of captopril based on its enhancing effect on the luminol-ferricyanide/ferrocyanide reaction. Luminescence 2002 17 169-172. 

The Hill reaction can be monitored by measuring the oxygen produced with an oxygen electrode or a Warburg manometer, or by spectrophotometry. The ferricyanide - ferrocyanide reduction can readily be measured by the last method ferrocyanide acceptor and spectrophotometry are therefore used to measure the Hill reaction inhibiting effect of herbicides (Hill, 1937, 1940, 1965). 

In the ferricyanide-ferrocyanide-N20 and 02-H+-C2H50H system (45), maximum doses are missing, but in the latter system, the pH effect can be attributed to the competition of electrons on the 02 and aldehyde formed, while at low pH, H atoms would probably react with 02 only. 

As an example, let s take the well-known reversible reaction of ferricyanide/ferrocyanide on an RRDE with Pt as ring and Pt as disk electrodes ... 

Fig. 1 Cyclic voltammogram at the water l,2-dichloroethane interface in the presence of ferricyanide/ferrocyanide coupie and ferrocene (Fc) at 10 mV. This experiment was performed with a four-electrode potentiostat, while the electrochemical cell can be represented as...

Fig. 2 Cyclic voltammograms of the heterogeneous reduction of tetracyanoquinodimethane (TCNQ) by the ferricyanide/ferrocyanide couple across the water DCE interface at various scan rates (a). The composition of the electrochemical cell is as in Fig. 1 but with a ratio 0.01 /0.4 M Fe(CN)6 /Fe(CN)6 and 6 lO- M TCNQ in DCE. Absorption spectra obtained in total internal reflection from the DCE phase as the potential is swept from 0.190 to 0.260 V, with a difference 40 mV between each spectrum (b). The spectra show the main features of the radical TCNQ as the potential is swept toward the reduction potential. (Fig. 2a was reprinted from Ref [25] with permission from Royal Society of Chemistry. Fig. 2b was reprinted from Ref [26] with permission from Elsevier Science.)...

A way to reduce interferences by cooxi-dizable sample constituents is by keeping the applied electrode potential as low as possible. Therefore, a reaction partner is chosen to be electrochemically indicated that is converted at low potential. For this purpose, the natural electron acceptors of many oxidoreductases have been replaced by redox-active dyes or other reversible electron mediators. Among them are the ferricyanide/ferrocyanide couple, V-methylphenazinium sulfate, fer-rocenes, and benzoquinone. With these mediators an electrode potential around -1-200 mV can be applied, which decreases... 

A commonly used mediator is the ferricyanide/ferrocyanide couple, and Equations (10.9) and (10.10) show the reaction sequence involved ... 

Ferricyanide-ferrocyanide (both potassium salts) for morphine. 

Now let us turn to the process in solution, the ferricyanide/ferrocyanide transition. The free energy change associated with the transfer of an electron to an oxidized species in solution can be viewed in the context of a thermodynamic cycle (Figure 1-2). 

For ferricyanide/ferrocyanide versus the silver chloride reference, this is ... 

---