Reverse differential pulse voltammetry

They are applicable to electrodes of any shape and size and are extensively employed in electroanalysis due to their high sensitivity, good definition of signals, and minimization of double layer and background currents. In these techniques, both the theoretical treatments and the interpretation of the experimental results are easier than those corresponding to the multipulse techniques treated in the following chapters. Four double potential pulse techniques are analyzed in this chapter Double Pulse Chronoamperometry (DPC), Reverse Pulse Voltammetry (RPV), Differential Double Pulse Voltammetry (DDPV), and a variant of this called Additive Differential Double Pulse Voltammetry (ADDPV). A brief introduction to two triple pulse techniques (Reverse Differential Pulse Voltammetry, RDPV, and Double Differential Triple Pulse Voltammetry, DDTPV) is also given in Sect. 4.6. 

Cyclic Voltammetry. However, experimental use of this technique has been restricted almost exclusively to the analysis of the limiting currents of the signals obtained. One reason for this could be that when a quasi-reversible electronic transfer is analyzed in RPV, two very close waves are obtained, which are difficult to resolve from an experimental viewpoint. This problem can be eliminated by using the triple pulse technique Reverse Differential Pulse Voltammetry (RDPV), proposed in references [80, 84, 85] and based in the application of the waveform presented in Scheme 4.5. 

Molecular Characterization It has been repotted that o-qulnones oxidize ascorbic acid In homogeneous solutions (25). Surface qulnones have also been reported to exist on activated carbon surfaces (16). However, cyclic voltarammetry Is not sufficiently sensitive to allow an unambiguous Identification of the reversible wave ascribed to surface qulnones (16). Therefore, differential pulse voltammetry (DPV) and square wave voltammetry were employed. 

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. 

An alternative and more recent electroanalytical tool is square-wave voltammetry (which is probably now employed more often than normal or differential pulse voltammetry). In this technique, a potential waveform (see Figure 6.26) is applied to the working electrode. Pairs of current measurements are then made (depicted on the figure as t and f2) these measurements are made for each wave period ( cycle ), which is why they are drawn as times after to (when the cycle started). The current associated with the forward part of the pulse is called /forward, while the current associated with the reverse part is /reverse- A square-wave voltammogram is then just a graph of the difference between these two... 

Fig. 2a) and differential-pulse voltammetry (DPV) (Fig. 2b), six successive, fully reversible, one-electron reductions are easily observed [31]. The potentials measured are shown on Table 2. As expected, on the basis of the triply degenerate LUMO, the potential separation between any two successive reductions is relatively constant, 450 50 mV. On the voltammetric timescale, Cgo through Cgo appear to be chemically stable. However, only Cgo through Cgo are stable when generated by controlled potential coulometry (CPC) under vacuum, using toluene/acetonitrile as solvent. 

In addition to the traditional SEV techniques discussed earlier, various pulse volt-ammetric techniques have been employed at solid electrodes in molten salts, especially in the room-temperature haloaluminate melts. Numerous pulse techniques have been devised, and some of the more common examples of this family of volt-ammetric methods are described in Chapters 3 and 5 of this volume. However, the application of these methods to molten salts is limited primarily to large amplitude pulse voltammetry (LAPV), differential-pulse voltammetry (DPV), and, more recently, reverse normal-pulse voltammetry (RNPV). The application of LAPV and... 

The elimination of the capacitive current in the case of - differential pulse voltammetry (DPV) is achieved by sampling the current twice before pulse application and at the end of the pulse. The basis for that elimination is the very different time dependence of both current components Ic exponentially dropping with time, and If decreasing with r1/2, at least in reversible cases (- Cottrell equation). 

See -> differential pulse voltammetry, - normal pulse voltammetry, and -> reverse pulse voltammetry. 

Potentiodynamictechniques— are all those techniques in which a time-dependent -> potential is applied to an - electrode and the current response is measured. They form the largest and most important group of techniques used for fundamental electrochemical studies (see -> electrochemistry), -> corrosion studies, and in -> electroanalysis, -+ battery research, etc. See also the following special potentiodynamic techniques - AC voltammetry, - DC voltammetry, -> cyclic voltammetry, - linear scan voltammetry, -> polarography, -> pulse voltammetry, - reverse pulse voltammetry, -> differential pulse voltammetry, -> potentiodynamic electrochemical impedance spectroscopy, Jaradaic rectification voltammetry, - square-wave voltammetry. 

Pulse voltammetry — A technique in which a sequence of potential pulses is superimposed to a linear or staircase voltage ramp. The current is usually measured at the end of the pulses to depress the - capacitive (charging) current. Depending on the way the pulses are applied and the current is sampled we talk about - normal pulse voltammetry, reverse pulse voltammetry and - differential pulse voltammetry. Several other, less popular pulse techniques are offered in commercial voltammetric instrumentation. Some people consider - square-wave voltammetry as a pulse technique. 

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... 

Figure 18 Under the appropriate experimental conditions (PhMe/ MeCN, — 10°C), Ceo undergoes six reversible one-electron reductions (a) cyclic voltammetry, (b) differential pulse voltammetry. C70 displays similar properties. (Reprinted with permission from Ref. 61. 1992 American Chemical Society)...

NPV), differential pulse voltammetry (DPV) and SWV, and polarography methods (use of a mercury drop electrode) like normal (normal and pulse polarography (NPP)) and DPP, although sometimes these polarographic versus voltammetric terms are used interchangeably. These step methods do not typically use return scans and therefore often do not provide information about reversibility of the redox process and can sometimes give data that, unknown to the researcher, are characteristic of decomposition products. 

Differential Pulse Voltammetry (DPV). There are two main differences between differential pulse and NPV. The waveform for DPV, Figure 10(b), involves a pulse of amplitude AEpuise like that of the normal pulse sequence but the step back down is not to the initial potential, instead it is to a specific differential that is used during the measurement. Also, there are two sampling periods for each pulse, once at the end of the potential step up, like in NPV, and an additional sampling period at the end of the step down in potential, after which the difference in the two signals is recorded hence the name DPV. This pulse sequence results in a current signal response different from that of NPV, shown in Figure 10(b). If the electrochemical process is reversible, the peak half width, A p/2, is determined by equation (9), ... 

We will consider five subtopics tast polarography and staircase voltammetry, normal pulse voltammetry, reverse pulse voltammetry, differential pulse voltammetry, and square wave voltammetry. Tast polarography, normal pulse voltammetry, and differential pulse voltammetry form a sequence of development rooted historically in polarography at the DME. To illustrate the motivating concepts, we will introduce each of these methods within the polarographic context, but in a general way, applicable to both the DME and SMDE. Then we will turn to the broader uses of pulse methods at other electrodes. Reverse pulse voltammetry and square wave voltammetry were later innovations and will be discussed principally outside the polarographic context. 

Yeh and Kuwana " were the first to report on the electrochemistry of cytochrome c at doped metal oxide semiconductor electrodes. A nearly reversible electrode reaction was indicated by the cyclic voltammetry and differential pulse voltammetry of cytochrome c at tin-doped indium oxide electrodes. Except for the calculated diffusion coefficient, all of the characteristics of the electrochemistry of cytochrome c at this electrode indicated that the electrode reaction was well-behaved. A value of 0.5 x 10" cmVs was determined for the diffusion coefficient which, like previously determined values at mercury, is lower than the value obtained by nonelectrochemical methods (i.e., 1.1 X 10 cm /s " " ). The electrochemical response of cytochrome c at tin oxide semiconductor electrodes was reported to be quasi-reversible, although no details were given. " ... 

Each electroanalytical technique has certain characteristic potentials, which can be derived from the measured curves. These are the half-wave potential in direct current polarography (DCP), the peak potentials in cyclic voltammetry (CV), the mid-peak potential in cyclic voltammetry, and the peak potential in differential pulse voltammetry (DPV) and square-wave voltammetry. In the case of electrochemical reversibility (see Chap. 1.3) all these characteristic potentials are interrelated and it is important to know their relationship to the standard and formal potential of the redox system. Here follows a brief summary of the most important characteristic potentials. 

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