Square-wave amplitude peak potential

Figure 2.23b shows the dependenee of the net peak potentials on the logarithm of the parameter A. If the film is very thin (A < 0.1), this relationship is linear, with the slope dE /d log A = 2.3RTjnF. On very thiek films (A > 10) the net peak potential is independent of A, regardless of square-wave amplitude. So, if at the lowest frequency A > 10, the net peak potential is independent of frequency. On... 

Table 3.2 Peak current ratios for commercial iron oxide (FeiO-, Aldrich) and earth pigments from Kremer. From square-wave voltammograms of sample-modified PlGEs immersed into 0.10 M HCl. Potential step increment 4 mV square wave amplitude 25 mV frequency 5 Hz. Adapted from ref. [139]...

Fig. 4.9 Theoretical variation of the Tafel ordinate at the origin for azurite + smalt mixtures taking peak potential separations (from upper to below) of 0, 50, 75, and 100 mV. Data points correspond to synthetic specimens containing pure azurite, pure smalt, and 70 30, 50 50, and 30 70 (%, w/w) azurite-smalt mixtures. From SQWVs at specimen-modified PIGEs, immersed into 0.50 M phosphate buffer, pH 7.4 initiated at +0.65 V in the negative direction. Potential step increment 4 mV square-wave amplitude 20 mV frequency 5 Hz [133]...

Fig. 4.18 Stripping oxidation peaks recorded for (a) Sn02 plus auxiliary clay (50%, 50% w/w mixture), and (b) Sn02 plus PbCOs plus auxiliary clay (20%, 40%, 40% w/w mixture) specimens attached to PlGEs in contact with 0.50 M acetate buffer. Square-wave voltammograms initiated at — 1.05 V after an electrodeposition step of 30 s at that potential. Potential step increment 4 mV square-wave amplitude 25 mV frequency 15 Hz [242]...

As in the case of a reversible one-electron electrochemical reaction, the halfpeak width of the SWV does not depend on the electrode geometry. For a two-electron electrochemical reaction, Wy2 is only a function of the difference between formal potentials AE f and of the square wave amplitude sw. The evolution of the half-peak width Wy2 with AEcspherical electrodes has been plotted in Fig. 7.32. These curves give a very general criterion for the characterization of the EE process through Wy2. 

The influence of the reversibility of the electrochemical reaction on the SW net charge-potential curves ( (Gsw/Gf) - (Eindex is plotted in Fig. 7.48 for different values of the square wave amplitude ( sw = 25,50,100, and 150mV) and three values of the dimensionless surface rate constant (1° ( k°t) = 10,0.25, and 0.01), which correspond to reversible, quasi-reversible, and fully irreversible behaviors. Thus, it can be seen that for a reversible process (Fig. 7.48a), the (Gsw/Gf) — (Eindex EL°) curves present a well-defined peak centered at the formal potential (dotted line), whose height and half-peak width increase with Esw (in line with Eqs. (7.118) and (7.119)), until, for sw > lOOmV, the peak becomes a broad plateau whose height coincides with Q s. This behavior can also be observed for the quasi-reversible case shown in Fig. 7.48b, although in this case, there is a smaller increase of the net charge curves with sw, and the plateau is not obtained for the values of sw used, with a higher square wave amplitude needed to obtain it. Nevertheless, even for this low value of the dimensionless rate constant, the peak potential of the SWVC curves coincides with the formal potential. This coincidence can be observed for values of sw > 10 mV. 

The second procedure is based on the effect of the square wave amplitude on the peak potential separation between the anodic and cathodic components of the SWV response. This separation depends on both the reversibility of the surface charge transfer (through co and Sw- Thus, by plotting the differences AEp = Epc — E pl>, with Ep c and EpA being the peak potentials of the forward and reverse currents measured versus the index potential, or AE p = Ef c — E p a with h p c and h p a being the peak potentials of the forward and reverse currents measured versus the real potential that is applied in each case (potential-corrected voltammograms), it is possible to obtain linear dependences between the peak potentials separation and... 

The peak currents and potentials of the forward and backward components are listed in Table II.3.2. If the square-wave amplitude is not too small nEsw > 10 mV), the backward component indicates the reversibility of the electrode reaction. In the... 

Square-wave voltammetry The potential-time waveform and current measuring scheme for this technique is shown in Fig. 10. The waveform consists of a symmetrical square-wave (peak to peak amplitude 2Es ) superimposed on a staircase wave of step height AE and a period t. The response current is sampled at the end of both the forward (If) and reverse (If) half cycle. A difference current dl is determined as... 

The peak current depends on the square-wave amplitude E, and the potential increment AE in the same way as in the case of the simple reaction (Eq. II.3.1) (see Table II.3.1). The half-peak width also depends on the amplitude and has no diagnostic value. However, the response of the reversible reaction (II.3.5) is narrower than the response of the reversible reaction (Eq. II.3.1). If nE y = 50 mV and tiAE = 10 mV, the half-peak widths are 100 mV and 125 mV, respectively [88]. 

Table 2.1 Square-wave voltammetry of fast and reversible electrode reaction (1.1). The dimensionless net peak current, the ratio of peak currents of the forward and backward components, the peak potentials of the components and the half-peak width as functions of SW amplitude ...

Detection The guanine oxidation peak was measured in an unstirred ABS using square-wave voltammetric scan (frequency — 200 Hz, step potential — 15 mV, amplitude = 40 mV),... 

This equation indicates that the peak potential is located at more negative values than E 1 and it moves toward the formal potential as Esw increases. When high values of the square wave pulse amplitude are used, the Q — E curves show a broad plateau which is centered at a potential E Et° — (RT/(2F)) n + c). Another interesting characteristic of the Q, — E curve is the cross potential for which the converted charge is null. For reversible conditions, it is given by (see... 

The experimental / w/2f (E E ) and (2sw — (E — E ) curves of the FcC()SH C4SH mixed monolayer at a disc gold electrode of 100 pm diameter in a solution 1.0 M NaCICU, obtained for different values of the square wave pulse amplitude and a fixed ferricyanide concentration 10 mM, are plotted in Fig. 7.58. It can be seen that whereas the peak height of the charge-potential curves increases with sw until charge plateau for sw > 110 mV is obtained, the anodic limit region remains unaffected, in line with Fig. 7.57b and Eq. (7.150). From the measurement of the charge plateau for sw = 130 mV, the value... 

The one-drop square wave analyser designed by Osteryoung and co-workers [66,67] filled the gap the specific commercial Instrumentation Isft In this voltammetrlc mode. The Instrument, depicted In Fig. 11.13, has the following features a symmetrical square wave with a period of 1/60 s and a fixed-wave peak-to-peak amplitude of 50 mV, providing a reasonable compromise between resolution and sensitivity. The remainder of the experimental parameters (e.g. the step height, Initial potential and delay time) are selected by the oper-... 

In EIS one can use potential or current sinusoidal perturbations. In practice, the potential perturbation of 10 mV peak to peak or a 5 mV amphtude is usually used because EIS is based on the linearization of nonlinear electrochemical equations. This also means that as the sum of sine waves is appUed, its total amplitude cannot exceed 5 mV. In practice amplitude of 5 mV rms is usually used for diffusion and adsorption limited processes, see Sect. 13.2, but in certain cases of surface processes where sharp voltammetric peaks appear the amplitude should be much lower. The linearity can be simply checked by decreasing amplitude and comparing the obtained results. Sect. 13.2. It should be kept in mind that the apparatus used in electrochemistry displays the root-mean-squared (rms) amplitude, which is the effective amplitude measured by an ac voltmeter. This rms amplitude is equal to the real amplitude divided by V ... 

Similar to EIS, SWV (square-wave voltammetry) is another frequency-dependent electrochemical technique that could also be used in label-free Faradaic immunosensing [167]. In this case, a train of potential pulses is superimposed on a staircase potential signal with the latter centered between a cathodic pulse and an anodic pulse of the same amplitude. During each cathodic pulse, the analyte diffuses to the electrode surface and it is immediately reduced. During the anodic pulse, analyte that was just reduced is reoxidized. The current is sampled just before and at the end of each pulse and the current difference between these two points is then plotted against the staircase potential in a SW voltammogram. A linear potential scan in SWV is faster than EIS record and a familiar peak-shaped signal is more easily interpreted. 

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