Ferri/ferrocyanide system, electrochemical

Pulsed-current techniques can furnish electrochemical kinetic information and have been used at the RDE. With a pulse duration of 10-4 s and a cycle time of 10-3 s, good agreement was found with steady-state results [144] for the kinetic determination of the ferri-ferrocyanide system [260, 261], Reduction of the pulse duration and cycle time would allow the measurement of larger rate constants. Kinetic parameter extraction has also been discussed for first-order irreversible reactions with two-step cathodic current pulses [262], A generalised theory describing the effect of pulsed current electrolysis on current—potential relations has appeared [263],... 

At the present time, the theory of electrochemical impedance of electrodes with distributed potentials is not yet completed, and algorithms of parametrical and structural identification procedures are not available. In addition, the interpretation of the results is very complicated. For this reason, in this work we analyzed only the frequency characteristics of impedance s components in the modified electrode system. As a result, we obtained a set of response peculiarities in the frequency range under investigation. Rather low frequency dispersion was observed in a solution containing a ferri-ferrocyanide system for both active (Fig.3, curve 2) and reactive (Fig.4, curve 3) components. In our opinion, this fact confirms that the independent on frequency resistance of charge transfer determines the main contribution to the impedance. 

An alternative approach used the same sensor electrode, but DNA hybridization was detected by electrochemical impedance spectroscopy (EIS), which eliminates the necessity of applying a redox-labeled reporter oligonucleotide (Kafka et al., 2008). The ferri-/ferrocyanide system was used as a redox probe instead. DNA immobilized on the gold electrode affected the electrochemical conversion of the negatively charged ferri- and ferrocyanide ions, as depicted in Figure 4.2. 

Motivated by the possible catalyst interference in the electrochemical response of the nanotubes, Jones et al. studied the response of HOPG electrodes modified by catalyst-free CNTs. At least relative to the ferri/ ferrocyanide system, the study revealed that the electrodes were reversible and the peak current obtained was proportional to the amount of tubes. According to the authors, this response demonstrates the noninterference of the catalyst in the response of the nanotube probe (Ai p 60 mV) and the contribution of the amount of CNTs to the peak current of the electrode. The authors also observed that the same electrode modified with Bamboo like nanotubes features 66 mV peak separation. 

In this paper, we explain throughly this modeling methodology for the rotating disk electrode (RDE) and the inverted rotating disk electrode (IRDE) configurations. The modeling and quantification of the electrochemical parameters are applied to redox reactions with one electron transfer mechanism the ferri/ferrocyanide system and the hexaammineruthenium (HI) / (II) system. 

A wide variety of enzymes have been used in conjunction with electrochemical techniques. The only requirement is that an electroactive product is formed during the reaction, either from the substrate or as a cofactor (i.e. NADH). In most cases, the electroactive products detected have been oxygen, hydrogen peroxide, NADH, or ferri/ferrocyanide. Some workers have used the dye intermediates used in classical colorimetric methods because these dyes are typically also electroactive. Although an electroactive product must be formed, it does not necessarily have to arise directly from the enzyme reaction of interest. Several cases of coupling enzyme reactions to produce an electroactive product have been described. The ability to use several coupled enzyme reactions extends the possible use of electrochemical techniques to essentially any enzyme system. 

Peak potentials and peak currents are useful diagnostic parameters to calculate in CV. In diffusing, reversible systems such as ferri/ferrocyanide, the straightforward relations in Table 5.2 can be used to extract estimates of formal potential, reversibility, and even diffusion coefficients. Understanding how to extract parameters from known electrochemical systems will help users identify trends in less well-known biofilm systems. 

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