Voltammetric techniques cyclic

The Model 384B (see Fig. 5.10) offers nine voltammetric techniques square-wave voltammetry, differential-pulse polarography (DPP), normal-pulse polar-ography (NPP), sampled DC polarography, square-wave stripping voltammetry, differential pulse stripping, DC stripping, linear sweep voltammetry (LSV) and cyclic staircase voltammetry. 

This is a dynamic electrochemical technique, which can be used to study electron transfer reactions with solid electrodes. A voltammo-gram is the electrical current response that is due to applied excitation potential. Chapter 18b describes the origin of the current in steady-state voltammetry, chronoamperometry, cyclic voltammetry, and square wave voltammetry and other pulse voltammetric techniques. 

These arguments were apparently in contradiction with electrochemical results reported by Cruanes et al. (158), according to which the reduction of cytochrome c is accompanied by a volume collapse of 24 cm3 mol-1. This value is so large that it almost represents all of the reaction volume found for the investigated reactions discussed above. A reinvestigation of the electrochemistry of cytochrome c as a function of pressure, using cyclic and differential pulse voltammetric techniques (155), revealed a reaction volume of -14.0 0.5 cm3 mol-1 for the reaction... 

The electrochemical properties of these molecules were investigated using cyclic and square-wave voltammetric techniques and it was found that they all exhibited similar electrochemical properties (Chen et al., 1994). 

Electrochemical studies of the behaviour of [100] (5 X 10 4 mol dm-3 in dichloromethane solution containing 0.1 mol dm-3 [NBu"]BF4 as supporting electrolyte) have been carried out using cyclic and square-wave voltammetric techniques. The receptor itself undergoes two quasi-reversible oxidations at Epi = +350 mV and Ep2 = +450 mV referenced to Ag/Ag+. Rotating disk... 

The most popular voltammetric technique is probably cyclic voltammetry (CV), partly because of its early development in theory and the availability of the corresponding commercial equipment. In this technique, the electrode potential is first scanned linearly with time from a starting potential, where no reaction occurs, passing E°, towards another potential, and then reversed back to the starting potential. In this case, the time variable can be conveniently represented by the scan rate, v. 

Cyclic voltammetry belongs to the category of voltammetric techniques based on a linear potential sweep chronoamperometric technique. It certainly constitutes the most useful technique for a preliminary determination of the redox properties of a given species. 

In linear sweep voltammetric techniques the applied electrode potential is varied from an initial value E to a final value f at a constant scan rate v (single sweep voltammetry). Once the value is reached the direction of the scan can be reversed, maintaining the same scan rate v, and the potential brought back to the initial value (cyclic voltammetry). In the two cases the form of the potential-time impulse can be represented as shown in Figure 1. 

It is conceivable that the presence of such complications must affect the shape of the cyclic voltammograms, and hence perturb to some extent the diagnostic criteria for the above-mentioned fundamental electron transfer processes. As these reactions proceed at their own rates, cyclic voltammetry will be able to detect them only if their rates fall within the time scale of the voltammetric technique (which ranges from a few tens of seconds to a few milliseconds). 

Quantitative investigations of the kinetics of these a-coupling steps suffered because rate constants were beyond the timescale of normal voltammetric experiments until ultramicroelectrodes and improved electrochemical equipment made possible a new transient method calledjhst scan voltammetry [27]. With this technique, cyclic voltammetric experiments up to scan rates of 1 MV s are possible, and species with lifetimes in the nanosecond scale can be observed. Using this technique, P. Hapiot et al. [28] were the first to obtain data on the lifetimes of the electrogenerated pyrrole radical cation and substituted derivatives. The resulting rate constants for the dimerization of such monomers lie in the order of 10 s . The same... 

Figure 6.5 Potential is varied at a constant rate of dE/dt during voltammetric techniques such as polarography, linear sweep voltammetry and cyclic voltammetry. The scan rate v is always cited as a positive number.

The electrochemistry of dioxoruthenium(VI) and dioxoosmium(VI) complexes with polypyridyl and macrocyclic tertiary amine ligands has been extensively studied by cyclic voltammetric techniques. In general, cA-dioxo species have higher reduction potentials than the corresponding trans-Aiaxo species. " " For the trans-Aioxo species, the d, orbital ordering... 

Two voltammetric techniques, stationary-electrode voltammetry (SEV) and cyclic voltammetry (CV), are among the most effective electroanalytical methods available for the mechanistic probing of redox systems. In part, the basis for their effectiveness is the capability for rapidly observing redox behavior over the entire potential range available. Since CV is an extension of SEV, many points pertinent to CV are discussed in the SEV section. 

Recent studies describe the use of cyclic voltammetry in conjunction with controlled-potential coulometry to study the oxidative reaction mechanisms of benzofuran derivatives [115] and bamipine hydrochloride [116]. The use of fast-scan cyclic voltammetry and linear sweep voltammetry to study the reduction kinetic and thermodynamic parameters of cefazolin and cefmetazole has also been described [117]. Determinations of vitamins have been studied with voltammetric techniques, such as differential pulse voltammetry for vitamin D3 with a rotating glassy carbon electrode [118,119], and cyclic voltammetry and square-wave adsorptive stripping voltammetry for vitamin K3 (menadione) [120]. 

Equation (6.96) can be applied to any sequence of constant potential pulses and so to any voltammetric technique. In the particular case of cyclic voltammetry, the waveform is given by Eq. (5.1) and the current takes the form... 

The kind of voltammetry described in Sect. 4.2. is of the single-sweep type, ie., only one current-potential sweep is recorded, normally at a fairly low scan rate (0.1-0.5 V/min), or by taking points manually. Cyclic voltammetry is a very useful extension of the voltammetric technique. In this method, the potential is varied in a cyclic fashion, in most cases by a linear increase in electrode potential with time in either direction, followed by a reversal of the scan direction and a linear decrease of potential with time at the same scan rate (triangular wave voltammetry). The resulting current-voltage curve is recorded on an XY-recorder,... 

For chemists, the second important application of electrochemistry (beyond potentiometry) is the measurement of species-specific [e.g., iron(III) and iron(II)] concentrations. This is accomplished by an experiment in which the electrolysis current for a specific species is independent of applied potential (within narrow limits) and controlled by mass transfer across a concentration gradient, such that it is directly proportional to concentration (/ = kC). Although the contemporary methodology of choice is cyclic voltammetry, the foundation for all voltammetric techniques is polarography (discovered in 1922 by Professor Jaroslov Heyrovsky awarded the Nobel Prize for Chemistry in 1959). Hence, we have adopted a historical approach with a recognition that cyclic voltammetry will be the primary methodology for most chemists. 

Electrochemical interconversion of homo- and heteronuclear gold cluster compounds remains an area that has received scant attention, despite the potential for changing the electron count and hence the metal cage geometries of these clusters by electrochemical methods. The electrochemical redox reactions of [Pt(AuPPh3)8]2+ have been studied, using pulse, differential pulse, and cyclic voltammetric techniques (124, 242) and two reversible, one-electron reduction steps have been... 

A very useful extension of the voltammetric technique is cyclic voltammetry (Adams, 1969 Cauquis and Parker, 1973) in which one scans the potential of the working electrode in an unstirred electrolyte solution in the anodic (cathodic) direction and records one or several peaks due to oxidation (reduction) of the substrate. At some suitable potential, the direction of the scan is reversed and peaks due to reduction (oxidation) of intermediates and/or products formed during the forward scan are observed. In the simplest case a linear increase (decrease) of the potential with time is employed (triangular cyclic voltammetry) with scan rates in the range 0 01-1000 V s 1. It should be noted that cyclic voltammetry at scan rates above 1 Vs"1 requires the use of a differential cell to reduce the residual current due to charging of the electrified interface (see, for example, Peover and White, 1967). The theory of cyclic voltammetry has been... 

The information that can be obtained with electrochemical detectors is not restricted to quantification. Instead of the conventional use of electrochemical detectors in amperometric mode at fixed potential, electrode arrays with each electrode held at different values of fixed potential can be used, in order to build up chronovoltammograms, three-dimensional current-voltage-time profiles. A 32-microband electrode array has been described for this purpose and applied to phenolic compounds [17] and which permits studying the electrode reaction mechanism at the same time as identification and quantification are carried out. Alternatively, fast voltammetric techniques such as fast-scan cyclic voltammetry or square wave voltammetry can be used to create chronovoltammograms of the eluted components. 

V V5. SCE, as measured by the cyclic voltammetric technique. Bulk electrolysis of CH2C12 solutions of [ReH(NCMe3)3(PPh3)2L]2+ affords purple [ReH(NCMe)3(PPh3)2L]3+, a rare example of a mononuclear hydrido-rhenium(IV) species.132... 

Figure 5 represents an ideal reversible one-electron transfer process in the absence of drop or capacitative charging current, although in real experiments contributions to the response from both these terms are unavoidable. Figure 6 shows the effect of uncompensated resistance for both transient and steady-state voltammograms, whilst Fig. 7 shows the influence of double layer capacitance on a cyclic voltammetric wave. Note that for steady-state voltammetric techniques only very low capacitative charging... 

Cyclic voltammograms can be presented in an alternative format to that shown in Fig. 5 by using a time rather than potential axis, as shown in Fig. 8. The equivalent parameters in steady-state voltammetric techniques are related to a hydrodynamic parameter (e.g. flow-rate, rotation speed, ultrasonic power) or a geometric parameter (e.g. electrode radius in microdisc voltammetry). 

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