Potential-time profile

Fig. 2. Common potential-time profiles used for the investigation of organic electrode processes. In each case the current response to the potential change is recorded.

In such a synthesis the lengths of the pulses are variable as well as the potentials of the square wave. Recently a potential-time profile has been used to maintain the activity of an electrode during the oxidation of organic compounds (Clark et al., 1972) at a steady potential the current for the oxidation process was observed to fall, but a periodic short pulse to cathodic potentials was sufficient to prevent this decrease in electrode activity. 

Such potential-time profiles (e.g. in Figures 6.2(a) and 6.5) still represent direct-current (DC) situations. 

Figure 3.17 Potential-time profiles for stationary electrode voltammetry.

Figure 3.2 Potential-time profile used for polarography and linear-sweep voltammetry (solid line) and cyclic voltammetry (both solid and dashed lines).

Fig. 13(a) Potential-time profile for a typical CV experiment, (b) coordinate system for a cyclic voltammetric experiment. 

The potential/time profile for anodic stripping voltammetry and a typical experimental curve for the determination of a mixture of heavy metal ions is shown in Fig. 11.14. The method is clearly limited to the determination of metals which form simple amalgams (inter-metallic compounds must also be avoided). This limitation, however, introduces some desirable selectivity and most organic compounds will not interfere with the determination of the metals. Using acceptable deposition times, analysis of very low concentrations is possible. Certainly for heavy metal ions, the sensitivity of anodic stripping analyses compares well with that of atomic absorption spectroscopy even with non-flame atomization (see Table 11.4). Moreover, these data do not represent the ultimate detection limit since the plating time can be extended. 

FIGURE 4.3.10. Oscillographic trace of a potential-time profile on a pure mercury cathode in 0.2N HCl at 1.5 Acm and -1.169V (SHE) [44]. (Reproduced by permission of The Electrochemical Society, Inc.)... 

Fig. 27. Pulse polarograms of 2 mM ferrioxalate complex in 0.1 M sodium oxalate and 0.1 M sodium perchlorate. Pulse polarographic modes (1) reverse, (2) normal the drop life = 0.36 s, the pulse width tp = 10.8 ms. The RP potential-time profile is sketched on the left side. Adapted according to [67].

Fig. 30. Potential-time profiles (A) of the alternating currents, (B) of the square-wave polarographic techniques, both on a negative ramp. Parameters the drop time, A and dEsw amplitudes of the potential waves. The relation z)Esw = dEAc holds.

Fig. 44. (A) Scheme of a single potential sweep on the DME of the life-time Starting (initial) potential Ej, final potential E delay time, t full line potential-time profile of the ramp capped at Ef dot-dashed line one LSV cycle with the sweep direction reversed (switched) at the potential E. (B) Scheme of the repeated cyclic potential sweeps between the constant starting and reverse potentials, Ej and Er, respectively.

Fig. 7. The potential-time profile applied in normal pulse voltammetry (a) and a normal pulse voltmamogram (b).

Differential pulse voltammetry This technique employs the potential-time profile as shown in Fig. 8 now the pulse height dE is kept constant (usually 25-100 mV) and the base potential is swept slowly with time. The current is sampled just before the application of the pulse (tsi) and just before the end of the pulse (132). Plot of the difference dl = I32 — against the potential at t3i yields the differential pulse voltammogram schematically shown in Fig. 8b. The peak of the reversible wave appears at E j2. 

Fig. 10. A potential-time profile in square-wave voltammetry (a) and square-wave voltam-mograms (b).

Figure 5.1 Potential-time profile for stripping voltammetry.

A potential-time profile as shown in Fig. 2.2 is then applied to the working electrode. Ei is chosen such that no reduction of 0, or indeed any other electrode reaction, occurs. Then at time r = 0 the potential is instantaneously changed to a new value 2, where the reduction of O occurs at a diffusion controlled rate. 

Fig. 2.2 - The potential-time profile for a single potential step chronoamperometric experiment.

Fig. 2.11 - Potential-time profile for double potential step studies of ec systems.

Fig. 2.17 - (a) The potential-time profile for differential pulse polarography. Also shown schematically, (b) the charging current-time dependence (c) the Faradaic current-time dependence, and (d) the time-dependence of the total current. 

B) Potential -time profile for the staircase voltage applied to the electrode (C) Current-potential response (polarogram). f , Measuring interval Time interval of the voltage step At sijp Voltage step of the applied staircase waveform... 

Finally, the concentration of metal(s) in the amalgam is determined by programming the electrode potential to values where the metal(s) are reoxidized to their ions in solution. In practice, the optimum presentation is obtained using the potential-time profile of differential pulse polarography. 

Fig. 2.9 Potential—time profiles used to perform linear sweep and cyclic voltammetry...

Additionally, as shown in Fig. 2.41, the potential—time profile can be used in ASV with a cleaning step (step A). This is usually applied in-between measurements to ensure that the deposited metal is fully stripped from the electrode surface so as to improve the reproducibility of the analytical measurement... 

Fig. 2.41 A typical experimental potential— time profile used in ASV. Step A is the Cleaning step , B electrodeposition, C Equilibration step , D Stripping step ...

Figure 7. Potential - time profile for the first cyde charge of an MCMB 2528 graphite anode In a C/UC0O2 cell at 25°C.

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