Voltammetry evaluation

PSS-SG composite film was tested for sorption of heme proteins hemoglobin (Hb) and myoglobin (Mb). The peroxidaze activity of adsorbed proteins were studied and evaluated by optical and voltammetric methods. Mb-PSS-SG film on PG electrode was shown to be perspective for detection of dissolved oxygen and hydrogen peroxide by voltammetry with linear calibration in the range 2-30 p.M, and detection limit -1.5 p.M. Obtained composite films can be modified by different types of biological active compounds which is important for the development of sensitive elements of biosensors. 

Cyclic voltammetry is the most widely used technique for acquiring qualitative information about electrochemical reactions. The power of cyclic voltammetry results from its ability to rapidly provide considerable information on the thermodynamics of redox processes, on the kinetics of heterogeneous electron-transfer reactions, and on coupled chemical reactions or adsorption processes. Cyclic voltammetry is often the first experiment performed in an electroanalytical study. In particular, it offers a rapid location of redox potentials of the electroactive species, and convenient evaluation of the effect of media upon the redox process. 

Cyclic voltammetry can also be used for evaluating die interfacial behavior of electro active compounds. Both the reactant and the product can be involved in an... 

Electrochemically active compounds can be evaluated using a potentiometer to generate a cyclic voltammogram for the analyte. Cyclic voltammetry will allow the analyst to determine whether the compound can be oxidized or reduced, to choose the appropriate potential to use in the electrochemical detector, and to establish whether oxidation or reduction is irreversible. Irreversible oxidation or reduction of the analyte could be predictive of problems with electrode poisoning and reduced sensitivity of the electrochemical detector over time. Turberg et al. used EC detection at an applied potential of -1-600 mV to analyze for ractopamine. 

The redox potential of Fc obtained from the cyclic voltammetry experiments at the water-DCE interface can be verified by evaluating the thermodynamic cycle given by Eq. (4). It follows that... 

The concentration of the transferred ion in organic solution inside the pore can become much higher than its concentration in the bulk aqueous phase [15]. (This is likely to happen if r <5c d.) In this case, the transferred ion may react with an oppositely charged ion from the supporting electrolyte to form a precipitate that can plug the microhole. This may be one of the reasons why steady-state measurements at the microhole-supported ITIES are typically not very accurate and reproducible [16]. Another problem with microhole voltammetry is that the exact location of the interface within the hole is unknown. The uncertainty of and 4, values affects the reliability of the evaluation of the formal transfer potential from Eq. (5). The latter value is essential for the quantitative analysis of IT kinetics [17]. Because of the above problems no quantitative kinetic measurements employing microhole ITIES have been reported to date and the theory for kinetically controlled CT reactions has yet to be developed. 

In this chapter, the voltammetric study of local anesthetics (procaine and related compounds) [14—16], antihistamines (doxylamine and related compounds) [17,22], and uncouplers (2,4-dinitrophenol and related compounds) [18] at nitrobenzene (NB]Uwater (W) and 1,2-dichloroethane (DCE)-water (W) interfaces is discussed. Potential step voltammetry (chronoamperometry) or normal pulse voltammetry (NPV) and potential sweep voltammetry or cyclic voltammetry (CV) have been employed. Theoretical equations of the half-wave potential vs. pH diagram are derived and applied to interpret the midpoint potential or half-wave potential vs. pH plots to evaluate physicochemical properties, including the partition coefficients and dissociation constants of the drugs. Voltammetric study of the kinetics of protonation of base (procaine) in aqueous solution is also discussed. Finally, application to structure-activity relationship and mode of action study will be discussed briefly. 

By varying the scan rate, this equation allows then the evaluation of the diffusion coefficient of the transferring ion. With the determination of the formal transfer potential of an ion and thus of its Gibbs energy of transfer by application of Eq. (10), this is the most important application of cyclic voltammetry. 

The Metrohm 646 VA processor and 647 VA stand is based on a polaro-graphic/voltammetric analyser with method memory and automatic curve evaluation, combined with a multi-mode stand (see Fig. 5.9). The following four determination techniques for polarography, voltammetry and stripping... 

The electrochemical behavior of niclosamide was described on the basis of d.c. polarography, cyclic voltammetry, a.c. polarography, and differential pulse polar-ography, in the supported electrolytes of pH ranging from 2.0 to 12.0 [32], A tentative mechanism for the reduction of niclosamide is proposed that involves the transfer of 4 e . Parameters such as diffusion coefficients and heterogeneous forward rate constant values were evaluated. 

The initial stages, notably the formation of a monolayer on a foreign substrate at underpotentials, were mainly studied by classical electrochemical techniques, such as cyclic voltammetry [8, 9], potential-step experiments or impedance spectroscopy [10], and by optical spectroscopies, e.g., by differential reflectance [11-13] or electroreflectance [14] spectroscopy, in an attempt to evaluate the optical and electronic properties of thin metal overlayers as function of their thickness. Competently written reviews on the classic approach to metal deposition, which laid the basis of our present understanding and which still is indispensable for a thorough investigation of plating processes, are found in the literature [15-17]. 

The cyclic voltammetry procedure reported by Kohen and others (2000) evaluates the overall reducing power of low-molecular-weight antioxidants in a biological fluid or tissue homogenate. The electrochemical oxidation of a certain compound on an inert carbon glassy electrode is accompanied by the appearance of the current at a certain potential. While the potential at which a cyclic voltammetry peak appears is determined... 

In particular, from the analysis in the very low frequency region, the limiting capacitance Q can be evaluated (via the limiting resistance R ). Practical cases have given values of Cj, of about 20mFcm (Panero et al, 1989), i.e. values of the same order as those obtained by cyclic voltammetry, thus confirming the validity of the charge saturation model. 

The applicability of the foregoing procednre has been tested by modeling simple reaction under semi-infinite diffusion conditions (reaction 1.1) and EC mechanism coupled to adsorption of the redox couple (reaction (2.177)) [2]. The solutions derived by the original and modified step-function method have been compared in order to evaluate the error involved by the proposed modification. As expected, the precision of the modified step-function method depends solely on the value of p, i.e., the number of time subintervals. For instance, for the complex EC mechanism, the error was less than 2% for p>20. This slight modification of the mathematical procedure has opened the gate toward modeling of very complex electrode mechanisms such as those coupled to adsorption equilibria and regenerative catalytic reactions [2] and various mechanisms in thin-film voltammetry [5-7]. 

The effectiveness of glassy-carbon electrodes coated with cellulose acetate for adsorptive stripping voltammetry was evaluated to alleviate interference from co-adsorbed species [171]. The carbon electrode was coated using a 5% cellulose acetate solution, with the coating being hydrolyzed with 0.07M potassium hydroxide. Repetitive measurements of 1 pM chlorpromazine in the presence of 20 mg/L albumin resulted in peak currents with residual standards of deviation equal to 1.4 and 1.3%, respectively. 

Labrador et al. (2009) developed a technique based on pulse voltammetry, used to predict concentrations of bisulfites, ascorbic acid, and histamine in wine samples, by means of PLS models evaluated via cross-validation. The best prediction results have been obtained for bisulfites. 

Gutes and coworkers presented an automated electronic tongue based on sequential injection analysis (SIA) and linear sweep voltammetry, for the simultaneous determination of glucose and ascorbic acid, by means of ANN regression. The models were evaluated with an external test set (Gutes et al., 2006). 

Coming to details, cyclic voltammetry was used to evaluate the activity of Ni3P2Wi8 and Mn2Ni4P3W24 in the electrocatalytic reduction of nitrate. The choice of the substrate is tricky, as nitrate is difficult to reduce. Other few examples... 

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