Differential pulse voltammetry peaks

TABLE 8.5 Square Wave Voltammetry or Differential Pulse Voltammetry Peak Potentials (in V Versus Fc + /Fc) of Multimetallofullerenes and Metal Carbide Fullerenes... 

Fig. 14 Optimization of hybridization conditions, (A) Plot of peak current response vs. incubation time (t from 10 min to 40 min), (B) Effect of hybridization temperature (from 40°Cto 70 °C), The differential pulse voltammetry peak current of CA-MB was detected in 0,1 M phosphate buffer saline solution pH 7,3, Reproduced from Li with permission... 

Selectivity Selectivity in voltammetry is determined by the difference between half-wave potentials or peak potentials, with minimum differences of+0.2-0.3 V required for a linear potential scan, and +0.04-0.05 V for differential pulse voltammetry. Selectivity can be improved by adjusting solution conditions. As we have seen, the presence of a complexing ligand can substantially shift the potential at which an analyte is oxidized or reduced. Other solution parameters, such as pH, also can be used to improve selectivity. 

The electrochemical response of analytes at the CNT-modified electrodes is influenced by the surfactants which are used as dispersants. CNT-modified electrodes using cationic surfactant CTAB as a dispersant showed an improved catalytic effect for negatively charged small molecular analytes, such as potassium ferricyanide and ascorbic acid, whereas anionic surfactants such as SDS showed a better catalytic activity for a positively charged analyte such as dopamine. This effect, which is ascribed mainly to the electrostatic interactions, is also observed for the electrochemical response of a negatively charged macromolecule such as DNA on the CNT (surfactant)-modified electrodes (see Fig. 15.12). An oxidation peak current near +1.0 V was observed only at the CNT/CTAB-modified electrode in the DNA solution (curve (ii) in Fig. 15.12a). The differential pulse voltammetry of DNA at the CNT/CTAB-modified electrode also showed a sharp peak current, which is due to the oxidation of the adenine residue in DNA (curve (ii) in Fig. 15.12b). The different effects of surfactants for CNTs to promote the electron transfer of DNA are in agreement with the electrostatic interactions... 

It has been demonstrated that the presence of CNTs greatly increases the oxidation peak current of 6-benzylaminopurine. The CNT-modified electrode is suitable for the determination of trace amounts of benzylaminopurine and has the advantages of high sensitivity, quick response, and good stability [86], Wang et al. have studied the electro-catalytic oxidation of thymine at a a-cyclodextrin incorporated CNT coated electrode in an alkaline media. A sensitive detection scheme for thymine has been further developed by using differential pulse voltammetry [87], The electrochemical determination... 

Electrochemical communication between electrode-bound enzyme and an electrode was confirmed by such electrochemical characterizations as differential pulse voltammetxy. As shown in Fig. 11, reversible electron transfer of molecularly interfaced FDH was confirmed by differential pulse voltammetry. The electrochemical characteristics of the polypyrrole interfaced FDH electrode were compared with those of the FDH electrode. The important difference between the electrochemical activities of these two electrodes is as follows by the employment of a conductive PP interface, the redox potential of FDH shifted slightly as compared to the redox potential of PQQ, which prosthetic group of FDH and the electrode shuttling between the prosthetic group of FDH and the electrode through the PP interface. In addition, the anodic and cathodic peak shapes and peak currents of PP/FDH/Pt electrode were identical, which suggests reversibility of the electron transport process. 

Conversely, since peaks are superimposed on a ramped baseline, the peaks obtained during differential pulse voltammetry are not square since the plateau of the peak increases at the constant rate of d /df that the baseline follows. 

Despite these possible drawbacks, differential pulse voltammetry is one of today s most popular electroanalytical tools. Its principal advantages over normal pulse voltammetry are twofold (i) many analytes can be sampled with a single voltammogram since the analytical peaks for each analyte are quite well resolved, and (ii) by working with a differential current, and hence obtaining a voltammetric peak, the analytical sensitivity can be improved to about 5 x 10 to mol dm. This sensitivity is clearly superior to normal pulse voltammetry. 

Differential pulse voltammetry is particularly susceptible to adsorption of species on the electrode, which can have drastic implications for peak shape. If adsorption is suspected, then peak area should be used rather than peak height... 

Method 1 - Anodic differential pulse voltammetry, involving voltage scanning from +0.3 to +1.0 V and recording the peak current, was found to yield an instrumental response proportional to the concentration of chlorpromazine in the range 9.6 to 340 pM. 

For compound (Scheme 1 and Table 1) the oxidation pattern is quite different the differential pulse voltammetry exhibits two peaks of equal height, both corresponding to a two-electron oxidation process (Figure 11). The first oxidation occurs at nearly the same potential as the four-electron process of compound 6F. This shows that, as expected, the two Os(bpy)2( i-2,3-dpp) units are the first to be oxidised (Table 2). The second process concerns the oxidation of the two Ru(bpy)2(p-2,5-dpp) units. Since such units lie far away from the previously oxidized Os-containing units, their oxidation occurs at a potential (Table 2) close to that of the equivalent peripheral units of 6D. As in the case of the compounds 6A-F the oxidation of the two inner units are displaced outside the accessible potential window. 

For lOA the differential pulse voltammetry exhibits only one six-electron peak which corresponds to the simultaneous one-electron oxidation of the six peripheral, noninteracting Ru units (Table 2 and Figure 13). Oxidation of the central and intermediate metal ions cannot be observed in the accessible potential window. 

The increase of the potential, at which the oxidation of the metal ions coordinated to the 2,3-Medpp ligand takes place, is further evidenced by the different behavior of the tetranuclear compound 4A and (Scheme 1 and Thble 1). As clearly indicated by the differential pulse voltammetry, which exhibits a three-electron oxidation peak for the former and a one-electron oxidation peak for the latter (Figure 14), in 4A the oxidation involves the three peripheral Ru units (as mentioned before), whereas in 4J, only the central Ru unit can be oxidized in the accessible potential window (Table 2). 

The step 2 product was evaluated in a 100-mM acetonitrile solution of tetrabutylam-monium hexalluorophosphate at scan rates of 25, 50, 100, 200, and 400 mV/s. The peak current for the reductive process was found to scale linearly with the scan rate suggesting that the step 2 product had adhered to the surface of the electrode. Cyclic voltammetry indicated a highest occupied molecular orbital (HOMO) of 4.7 eV with an electrochemical band gap of 1.65 eV. Differential pulse voltammetry gave rise to a HOMO of 4.67 eV. 

Electrochemical oxidation of natural and synthetic DNA performed at pyrolytic graphite [16] and glassy carbon [3-6,17,18] electrodes showed that at pH 4.5 only the oxidation of the purine residues in polynucleotide chains is observed. Using differential pulse voltammetry, the less positive peak corresponds to the oxidation of guanine residues and the peak at more positive potentials is due to the oxidation of adenine residues. 

Pang et al. [54] studied the electrochemical behavior of L-dopa at SWCNT-modified GCE. Before starting, the electrode was immersed for 120 s in the L-dopa solution. L-dopa showed an irreversible behavior at bare GCE with peak potential separation of 161 mV. On the contrary, a quasi reversible behavior with peak potential separation of 55 mV was obtained at the SWCNTs-modified electrode. Experiments performed by differential pulse voltammetry showed a... 

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