Cyclic voltammetric analyzer

After getting similar results with a standard electrochemical analyzer, the portable cyclic voltammetric analyzer was further applied to detect various concentrations of cyt c. The miniaturized screen-printed electrode-based cyt c biosensor CcR-CNT-PPy-SPE as designed and characterized in Chapter 3 was used here to detect cyt c. The electrocata-lytic activity of the miniaturized CcR-CNT-PPy-SPE hiosensor toward the determination of cyt c was assessed hy the developed low-cost, home-made cychc voltammetric instrument. The accuracy of the developed instrument was also evaluated hy comparing its results with that of a commercial electrochemical analyzer imder the same experimental conditions. 

The cyclic voltammogram is characterized by several important parameters. Four of these observables, the two peak currents and two peak potentials, provide the basis for the diagnostics developed by Nicholson and Shain (1) for analyzing the cyclic voltammetric response. 

Cyclic voltammetric (CV) experiments were done by using a BAS 100B electrochemical analyzer (USA). APt wire and Ag/AgCl electrode were used as the auxiliary and reference electrodes, respectively, and an ITO substrate, coated with one layer of PS I/PBV LB film, was used as the working electrode with 10 mmol/L KC1 as the electrolyte. An initial potential of -0.20 V was applied for 2 s, and subsequently cyclic scans to a final potential of -1.30 V were done for 10 cycles. All electrochemical measurements were done under an Ar atmosphere at room temperature. 

We examine next the cyclic voltammetric responses expected with nonlinear activation-driving force laws, such as the quasi-quadratic law deriving from the MHL model, and address the following issues (1) under which conditions linearization can lead to an acceptable approximation, and (2) how the cyclic voltammograms can be analyzed so as to derive the activation-driving force law and to evidence its nonlinear character, with no a priori assumptions about the form of the law. 

A reaction scheme frequently encountered in practice, the so-called square scheme mechanism, consists of the association of two EC reaction schemes as shown in Scheme 2.3 (which may as well be viewed as an association of two CE mechanisms). In the general case, the cyclic voltammetric response may be analyzed by adaptation and combination of the treatments given in Sections 2.2.1 and 2.2.2. A case of practical interest is when the follow-up reactions are fast and largely downhill. A and D are then stable reactants, whereas B and C are unstable intermediates. When the starting reactant is A (reduction process), the reaction follows the A-B-D pathway. The reoxidation preferred pathway is D-C-A. It is not the reverse of the forward... 

Polarographic and cyclic voltammetric data were analyzed for Mn complexes 76 (Z = O, S, NPh, NMe L = PPhj, CO). The differences between the half-wave potentials of the first and second reduction steps of 76 were appreciably smaller than those for the corresponding 2,4,6-triphenyl-substituted cations (90M13). 

Analyzing the data of Table 6 reveals that the results obtained by different authors in sodium salt solutions, at first sight, do not qualitatively agree with each other. Thus, in Refs. and only one oxidation peak (of solvated electrons or their associates) was observed on cyclic voltammetric curves during anodic sweep of potential. The slow potentiodynamic curves obtained initially by Kanzaki and Aoyagui have also one peak. In the much later works of these authors and... 

With the intense SERS signal provided by an Au substrate and a fast optical multichannel analyzer (such as, PDA or CCD), it is possible to obtain SERS of a surface reaction during the potential ramp, which is extremely important when irreversible processes occur. A good example is the combined SERS and cyclic voltammetric study of nitrobenzene surface reaction on a SERS-active Au surface. It is known that nitrobenzene can be reduced by three two-electron steps to form nitrosobenzene, phenylhydroxylamine and aniline ... 

With the development of 3-(co-bromoalkyl)thiophenes, several crown ether functionalized PTs have been synthesized by Bauerle and coworkers. Electropolymerization was performed on mono-, bi-, and terthiophene monomers 65-67 substituted with pendant 12-crown-4 receptor tethered with alkyl chains [175-177]. While electropolymerization failed with 65, compounds 66, 67, and 68 were easily electro-polymerized and the chemosensing properties of the polymers were analyzed. Cyclic voltammetric analysis showed that addition of increasing amounts of Li, Na, or produces a positive shift of the oxidation potential of poly(66, n=5), while this effect is less pronounced for poly(67). On the other hand, whereas the CV of poly(68, n=5) is strongly affected by the presence of alkali ions, the lengthening of the alkyl spacer in poly(68, n = 10) produces a complete loss of ion sensitivity. Optical and spectroelectrochemical experiments revealed that the changes in electronic properties were due to hindered diffusion of the counteranions into the film during polymer oxidation [177]. 

The catalytic responses may be analyzed in more details by extension of previous treatments of cyclic voltammetric catalytic currents [37, 38] so as to dispose of a tool to be used for extracting the pertinent rate constants from the experimental data. The two members of the cosubstrate couple, P and Q, diffuse to and from... 

Using either a lock-in amplifier or frequency response analyzer it is possible to study impedance during cyclic voltammetric dc potential cycling. During a slow voltammetric sweep, an ac signal can be superimposed and the ac response measured at one frequency at a time as a function of potential. If such an experiment is repeated at various frequencies, a complete impedance curve can be acquired, although for individual sweeps complex admittance is usually registered. 

Analyzing our experimental results in this same way we obtain values of y, which are in surprisingly good agreement with the values of / extracted from cyclic voltammetric data, suggesting that the error is tolerable. We have taken this as a good indication that the same redox population is sampled by the ILIT and cyclic voltammetric experiments (see Sec. VI.). In addition, we conclude that the excellent fits of the vs. 

This is our first encounter with the use of simulation to analyze CV results. Through the theory of simulation (Chapters 4-6), a cyclic voltammetric or potential step response can be calculated for any electrochemical mechanism, given the parameters that describe the experiment (scan rate, scan range, electrode area) and the mechanism (reduction potentials, electrode kinetics, chemical reaction kinetics, and diffusion coefficients of all chemical species). The unknown parameters of the electrochemical mechanism can be varied until a simulation is obtained that closely resembles the experimental result. 

For more complex electrode processes, cyclic voltammetric traces become more complicated to analyze. An example of one such case is the electroreduction of a species controlled by a preceding chemical reaction. The shape of the trace for this process is shown in Fig. 2.24. The species is formed at a constant rate at the electrode surface and, provided the diffusion of the inactive component is more rapid than its transformation to the active form, it cannot be depleted from the electrode surface. The peak current is thus independent of potential and resembles a plateau. 

Figure 5.44 Cyclic voltammetric curves recorded using our home-made portable electrochemical analyzer (a) and standard electrochemical analyzer (b) for 1 mM [Fe(CN)6] / containing 0.1 M KCI as supporting electrolyte on a bare SPE.

Cyclic and differential pulse voltammetric measurements were obtained from either 0.1 M TBAP/MeCl2 or 0.1 M TBAP/EtCl2 using a conventional three-electrode configuration and an IBM 225 voltammetric analyzer. A saturated calomel electrode (SCE) was used as a reference electrode in all... 

There are a few indirect methods for characterizing molecule-size physical recognition sites, such as examining the extent of monolayer penetration by probe molecules as a fiinction of their van der Waals radii and other chemical and physical properties (Scheme HI, Frame 4). We have used an electrochemical version of this approach, which assumes that the defect sites define an array of ultramicroelectrodes, to analyze our composite SAMs (Scheme IV). In these experiments, the shape of the cyclic voltammetric wave is correlated to the size and number density of sites through which the probe molecules can penetrate, as shown on the right side of Scheme IV (6). 

This sensor is better than a conventional Clark s device because there is no net consumption of any electrode. Both cyclic voltammetric and chronoamperometric measurements were carried out to analyze the performance of the microfabricated DO sensor. Good Unearity was observed when using 80 pm diameter electrode sets. 

Equation (25) is general in that it does not depend on the electrochemical method employed to obtain the i-E data. Moreover, unlike conventional electrochemical methods such as cyclic or linear scan voltammetry, all of the experimental i-E data are used in kinetic analysis (as opposed to using limited information such as the peak potentials and half-widths when using cyclic voltammetry). Finally, and of particular importance, the convolution analysis has the great advantage that the heterogeneous ET kinetics can be analyzed without the need of defining a priori the ET rate law. By contrast, in conventional voltammetric analyses, a specific ET rate law (as a rule, the Butler-Volmer rate law) must be used to extract the relevant kinetic information. 

The influence of the metal-support interaction on the electrocatalytic activity for methanol oxidation has been evaluated by analyzing the voltammetric behavior of various electrocatalysts differing in terms of surface properties, as expressed by their pHzpc but having similar average particle size (around 3nm). These data were combined with the information gained by cyclic voltammetry (CV) experiments in sulphuric acid electrolyte. In particular, the potential at which the onset of a Pt-OH layer formation on the surface occurs in the anodic sweep and the potential at which... 

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