Cyclic voltammetric stripping

The formation of a blocking film on an electrode surface will decrease the capacitance compared to that of the bare electrode, since the distance of closest approach of the counter ions, d, will be increased by the thickness of the layer [see (13.3.2) and Figure 14.5.5]. The extent of blocking by the monolayer and the presence of pinholes can be assessed in a number of ways (88). To obtain the aggregate area of the pinholes one can, for example, compare the sizes of voltammetric peaks for the bare and filmed electrode (such as those for the formation and reduction of an oxide layer on Au). To obtain the spatial distribution, one can deposit a metal like Cu, then strip the film and perform microscopy on the resulting surface. A frequently used procedure is to observe the chronoamperomet-ric or cyclic voltammetric behavior of an outer sphere species like Ru(NH3) in solution... 

Linear and cyclic voltammetric experiments were carried out by using a Metrohm E-612 scanner coupled to a Metrohm E-611 detector. Current-potential curves were recorded by a Graphtec WX-4421 X-Y recorder. A Metrohm 663 static mercury drop electrode (SMDE) with a drop area of 0.47 mm was used as working electrode for the stripping experiments. Potentials are referred to an Ag/AgCl/KCl 3 M electrode. 

Comparison of the half-wave potentials of the oxidizable and reducible forms of the redox reactants with the potentiometrically determined value of the standard redox potential is the simplest method for proof of reversibility and agreement between these two sets of data provides strong support for reversibility of the process being studied. However, in many polarographic reactions, it is found that one form of the conjugate redox pair is not sufficiently stable to be prepared or to permit determination of E% potentiometrically. In some of these cases, auxiliary methods can be used, particularly where the reactive species is relatively stable when formed at the surface of the mercury electrode. Such methods include the commutator method, an anodic stripping technique which has recently been reviewed by Barendrecht, and oscil-lopolarographic and cyclic voltammetric techniques. 

Fig. 6.22 Cyclic voltammetric responses of 0.5 mM As(III) in 0.1 M HCl at bare An electrode solid line), at carbon nanotubes (CNTs) (dashed line), and at Au nanoparticles/CNTs (dash dotted line) modified glassy carbon electrodes 0.1 Vs potential scan rate. Inset reports square wave anodic stripping voltammetric responses in 10-70 iiM As(III) solutions (pre-deposition —0.4 V vs. saturated calomel electrode for 120 s stripping /=50 Hz, s = 20 mV, AEs = 2 mV) (Adapted with permission of the authors. Reprinted from Ref. [222] with the permission of Elsevier)...

Such in-situ generated adsorption isotherms indicate different extents of surface coverage. The latter was estimated from controlled-adsorption/-cyclic voltammetric experiments. Values of 3.9 x 10 i , 5.9 x 10 , and 8.6 X 10-10 mol/cm2 (corresponding to 43, 32, and 19 nm /adsorbed molecule) were calculated for desipramine, imipramine, and trimipramine, respectively. It appears that minor differences in the side chain of antidepressants have a profound effect upon their orientation imipramine and desipramine yield the expected planar orientation of the tricyclic ring system and the carbon surface, while for trimipramine a vertically oriented adsorbed layer is indicated. Adsorption isotherms may be useful also for obtaining information regarding intermolecular interactions between absorbed molecules, as well as on interactions between adsorbed molecules and the surface. Concentration-induced orientational transitions may also be detected from the construction of adsorptive stripping calibration curves. 

The behavior of the anticancer agent cis-dichlorodiammineplatinum (II), or cisplatin, is another example of the utility of the method . The adsorptive-stripping/cyclic voltammetric (saturation) data yield a surface coverage of 5.1 x 10- o mol/cm. Each adsorbed molecule thus occupies an area of 33 A 2. This value is in excellent agreement with the area (34 A 2) estimated from the crystal structure of cisplatin. Such agreement suggests the existence of a packed geometrically planar layer of adsorbed cisplatin at the surface. 

We have thus demonstrated the feasibility of using BDD electrodes for the analysis of mercury and other trace metals. The effect of nitrate and chloride ions is very clearly evident from the cyclic voltammetric analysis. The presence of chloride enhances the stripping peak currents, but it forms insoluble calomel at the... 

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. 

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]. 

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. 

Figure 6.20 shows the repetitive cyclic voltammetry of the lithium deposition and stripping process on a nickel substrate from a cell using a (PE0)8LiCF3S03 polymer electrolyte, i.e. one of the first generation electrolytic membrane commonly used for the development of LPBs. The trend of the voltammetric curves indicates that the process at the lithium interface ... 

As it can provide some of the most basic electrochemical information related to the reactivity of the selected analyte (peak potential and peak current) most instruments that perform amperometry can also perform some of the most basic voltammetric techniques. These techniques determine the current as a function of the potential applied to the WE (in a conventional three-electrode cell) and can be performed with relatively simple instrumentation [105,106]. As different signals can be combined in the input ports of the instrument, multiple variations of the technique have been developed including cyclic voltammetry, linear sweep voltammetry, linear sweep stripping voltammetry, stripping voltammetry [107, 108], fast-scan cyclic voltammetry [109], square-wave voltammetry [110],and sinusoidal voltammetry [111]. 

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