Voltammetric methods cyclic

Cyclic voltammetry, square-wave voltammetry, and controlled potential electrolysis were used to study the electrochemical oxidation behavior of niclosamide at a glassy carbon electrode. The number of electrons transferred, the wave characteristics, the diffusion coefficient and reversibility of the reactions were investigated. Following optimization of voltammetric parameters, pH, and reproducibility, a linear calibration curve over the range 1 x 10 6 to 1 x 10 4 mol/dm3 niclosamide was achieved. The detection limit was found to be 8 x 10 7 mol/dm3. This voltammetric method was applied for the determination of niclosamide in tablets [33]. 

Cyclic voltammetric methods In these, the potential is swept linearly with time and the oxidation or reduction of the surface species can be followed by measuring the resultant current. Great care is needed in the interpretation of cyclic voltammograms and examples are given in chapter 2. 

The heterogeneous rates of electron transfer in eq 7 were measured by two independent electrochemical methods cyclic voltammetry (CV) and convolutive potential sweep voltammetry (CPSV). The utility of the cyclic voltammetric method stems from its simplicity, while that of the CPSV method derives from its rigor. 

This review concentrates on a special type which only recently has been investigated thoroughly and which has been designated as Weitz type . Here the heteroatoms X and Y are members of cyclic rr-systems showing quinoid (or polyenic) character in the reduced form RED. In the oxidized form OX, however, they exhibit aromatic behaviour. The potentials Ei and E2 can be determined by different voltammetric methods. 

Takamura et al. have reported a voltammetric method for the determination of chlorpromazine using an anodically oxidized carbon electrode [167]. A vitreous-carbon electrode was maintained at +1.6 V vi. S.C.E. for 2 minutes (in 0.5 M phosphate buffer at pH 6.8). Under these conditions, chlorpromazine gave an oxidation peak current on cyclic voltammograms that varied linearly with concentration over the range of 50 nM to 1 pM. 

Such objections do not apply to a redox-type situation (Fe + e = Fe ) and for which there are no radical intermediates. They apply only in a muted form when the cyclic voltammetric method is used in some kind of analysis of the content of the solution. However, they do apply to mechanism studies of electrochemical reactions involving intermediates as adsorbed radicals, and that means that they apply to mosl electrochemical reactions. 

Cyclic voltammetric methods, or other related techniques such as differential pulse polarography and AC voltammetry,3 provided a convenient method for the estimation of equilibrium constants for disproportionation or its converse, comproportionation. In this respect, the experimentally measured quantity of interest in a cyclic voltammetric experiment is E>A, the potential mid-way between the cathodic and anodic peak potentials. For a one-electron process, E,A is related to the thermodynamic standard potential Ea by equation (4).13 In practice, ,/2 = E° is usually a good approximation. 

When using microelectrodes to obviate resistance problems, it is convenient to develop a procedure to determine what conditions are required to reduce the error to an acceptable level. The results of such a procedure applied to disk electrodes are shown in Figure 16.6 [45]. In this and the remaining discussion, the technique of cyclic voltammetry is considered, as it is one of the most widely used voltammetric methods. The region of practical working conditions of electrode radius and scan rate is defined by the area set off by lines A, B, and C. 

Voltammetric methods in these methods, a potential is applied to the working electrode using a three-electrode setup (see section 1.6). The electrical current, resulting from charge transfer over the electrode-electrolyte interface, is measured and reveals information about the analyte that takes part in the charge transfer reaction. The potential applied can be constant (chronoamperometry, section2.5), varied linearly (cyclic voltammetry, section 2.3) or varied in other ways (Chapter 2). 

Electrochemical methods include potentiometry, cyclic voltammetry and chronoamperometry. These methods as well as other voltammetric methods and the impedance of electrochemical systems are discussed in this chapter. 

Another voltammetric method, sinusoidal voltammetry (SV), was also employed. This was a frequency-based electrochemical method, which was found to be more sensitive than the usual constant potential (DC) amperometric detection method. SV has been achieved to detect on-chip separated catecholamines. This method is very similar to fast-scan cyclic voltammetry (CV), except that a... 

Consequent upon the orbitals preferred for the unpaired electron, a high spin population occurs at C-4 in each of 1,52, and 53. These are the anion-radicals found to exhibit the least persistence.35 Relative reactivities of the anion-radicals have been estimated by a cyclic voltammetric method as 1 > 1,3,5-triazine anion-radical > 52 > 53 > 22 > 54, which corresponds with qualitative observations on persistence and accords very closely with the ranking order of maximum spin populations at carbon.119 120 Dimerization of the radicals at positions of high spin population at carbon is proved for 1 and 52, although the mechanism is by no means clear for 52 and other modes of reaction can also occur, e.g., proton abstraction from solvent or adventitious water.30,35,121-127... 

Cyclic voltammetric methods have been used for investigating surface oxygen compounds present on the surface of unmodified carbon materials, and in some cases, previously oxidized materials (electrochemically, oxygen rf-plasma, air, and steam), such as carbon blacks 9,10), gla.sslike carbon [11-15], graphite [16,17], carbon fibers [18-21], pyrolytic carbon [22,23] and active carbon [24-28],... 

The major voltammetric methods employed for studies of the anodic oxidation of aromatic hydrocarbons are linear sweep voltammetry (LSV), cyclic voltammetry (CV), and derivative cyclic voltammetry (DCV). Second harmonic ac (SHAC) voltammetry and... 

Part IV is devoted to electrochemical methods. After an introduction to electrochemistry in Chapter 18, Chapter 19 describes the many uses of electrode potentials. Oxidation/reduction titrations are the subject of Chapter 20, while Chapter 21 presents the use of potentiometric methods to obtain concentrations of molecular and ionic species. Chapter 22 considers the bulk electrolytic methods of electrogravimetry and coulometry, while Chapter 23 discusses voltammetric methods including linear sweep and cyclic voltammetry, anodic stripping voltammetry, and polarography. 

Diagnostic Electrochemical Measurements 12.3.2.1. Voltammetric Methods 12.3.2.1.4. Cyclic Voltammetry... 

Linear sweep and cyclic voltammetric methods have been employed for numerous basic studies of electrochemical systems and for analytical purposes. For example, the technique can be used for in vivo monitoring of substances in the kidney or brain (19) a typical example that employed a miniature carbon paste electrode to study ascorbic acid in a rat brain is illustrated in Figure 6.6.5. These techniques are especially powerful tools... 

An essential idea behind the normal pulse voltammetric method is the cyclic renewal of the diffusion layer. With either the DME or SMDE, renewal is achieved by the stirring accompanying the fall of an expended mercury drop and its replacement by a fresh drop. At other electrodes, renewal may not be easily accomplished. 

Once the system to simulate is properly described, we have to consider the electrical perturbation applied, that is, the electrochemical technique employed. This book will focus on the simulation of voltammetric techniques, and particularly of cyclic voltammetry, where the potential of the working electrode is varied according to different potential-time programs and the current response of the system is registered. Figure 1.10 outlines the potential-time programs and signals obtained for the main voltammetric methods. 

Electrochemical polymerization can be effected by potentiostatic, gal-vanostatic, or potentiodynamic (i.e., cyclic voltammetric) methods. In the gal-vanostatic mode, an amount of current is passed through the solution containing the monomer, and the polymer film is formed on the working electrode. In the potentiostatic mode the working electrode is kept at a potential at which polymerization takes place on the electrode. In the cyclic voltammetric method, the potential of the working electrode is scanned within a range determined by the oxidation potential of the polymer film. Potentiostatic and cyclic voltammetric formations of polymer films have wider applications in biosensor fabrication than the gal-vanostatic method. ... 

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