Square-wave amplitude frequency

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... 

Fig. 2.11 Square wave voltammograms for blanks of azurite and smalt, and for two samples from the Palomino s frescoes in the Sant Joan del Mercat church in Valencia, in contact with 0.50 M potassium phosphate buffer, pH 7.4 (a) azurite, (b) sample PV8b, (c) smalt, and (d) sample PA5b. Potential scan initiated at —0.85 mV in the positive direction. Potential step increment 4 mV square wave amplitude 15mV frequency 2Hz [133]...

Fig. 2.14 SQWVs of PIGEs modified with (a) Caput mortum, (b) Venetian red, immersed into 0.10 M HCl. Potential scan initiated at -1-0.65 V in the negative direction potential step increment 4 mV square wave amplitude 25 mV frequency 5 Hz [139]...

Fig. 2.16 SQWVs for silk fibers pigmented with (a) granado (b) alazor, (c) curcuma, (d) weld, and (e) cochineal red in contact with acetic/acetate buffer (total concentration 0.50 M) at pH 4.85. Potential step increment 4 mV square wave amplitude 25 mV frequency 5 Hz...

Fig. 2.20 SQWVs (first scan) of weld (a, b) and logwood (c, d) immersed into 0.25 M HAc + 0.25 M NaAc (a, c) and that electrolyte plus 0.05 M AICI3 (b, d). Potential step increment 4 mV square wave amplitude 25 mV frequency 15 Hz [124]...

M sodium acetate buffer, pH 4.85. Potential step increment 4 mV square wave amplitude 25 mV frequency 15 Hz [177]... 

Table 3.1 Diagnostic criteria for characterizing lead pigments via voltammetry of microparticles using deposits of the pristine pigments on parafiSn-impregnated graphite electrodes. Data from square-wave voltammograms at a potential step increment of 4 mV, square-wave amplitude of 25 mV, and frequency of 15 Hz. All potentials refer to AgQ (3M NaCl)/Ag. Electrolyte, 0.50 M acetate buffer, pH 4.85...

In these equations, Ej represents the electrode potential during the yth half period, 5 the fraction of the square-wave half period at which the current is measured, / is the square-wave frequency (equal to the inverse of the square-wave period), and the other symbols have their customary meaning. As long as the square-wave amplitude, Esw, is lower than 0.5RT jnF—a condition easily accomplished under the usual experimental conditions—the differential sum of the currents flowing during the anodic and cathodic half cycles can be represented by an expression such as [184]... 

Fig. 3.12 Tafel SL vs. 00 diagram for the most common copper pigments and copper alteration products. From SQWVs of specimen-modified paraffin-impregnated graphite electrodes immersed into 0.50 M phosphate buffer, pH 7.4. Potential scan initiated at -1-0.45 mV in the negative direction. Potential step increment 4 mV square wave amplitude 15 mV frequency 2 Hz...

Fig. 4.13 Square-wave voltammograms of PIGEs modified with mixtures of a zirconium-containing sample plus Zr02 (standard) and ZnO (auxiliary reference material) in contact with O.IOM VaCZ. Sample ZnO mass ratio equal to 4.422 ZnO Zr02 mass ratio equal to (a) 0.163 (b) 1.216 and (c) 5.374. Potential scan initiated at —1.45 V in the positive direction without prior electrodeposition step. Potential step increment 4 mV square-wave amplitude 25 mV frequency 15 Hz. [234]...

Fig. 4.16 Square-wave voltammograms for (a) alizarin (15.72%) + morin (7.16%) -I- silica (77.12%) and (b) alizarin (19.03%) + purpurin (8.30%) -I- raorin (12.48%) -I- silica mixtures (60.19%). Electrolyte 0.50M sodium acetate buffer, pH 4.90. Potential step increment 4 mV square-wave amplitude 25 mV frequency 15 Hz [241]...

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]...

Although the usual way of analyzing the influence of the kinetics of the electron transfer on the SWV response is based on the variation of the frequency at fixed values of the staircase and square wave amplitude, a new approach for carrying out this analysis has been proposed based on the study of the influence of the square wave amplitude sw on the current potential curves at a fixed value of the frequency (or the time pulse) [19, 33, 34], The square wave amplitude has been used rarely as a tool in mechanistic and kinetic studies. One of the main reason is that, as stated in Sect. 7.1, in SWV the current is plotted versus an index potential which is an average potential between the forward and reverse potentials (see Eq. (7.7)) and leads to a discrepancy between the plotted and actual potentials at which the current is sampled. Therefore, the role played by Esw in the process is complex. 

Equation (7.116) indicates that the charge-potential curves for reversible processes are only dependent on the square wave amplitude Sw and are independent of the frequency / = 1 jh and the staircase amplitude AEs. As a consequence, they are superimposable on those obtained at any differential electrochemical technique, such as DSCVC, provided that the differences between the successive potential pulses coincide (AE = 2 sw)- Moreover, when this difference is much less than RT/F (i.e., less than 25 mV at T = 198 K), the responses obtained in Cyclic Voltammetry (CV), Alternating Current Voltammetry, Potentiometric Stripping Analysis (PSA) and also in any Reciprocal Derivative Chronopotentiometry (RDCP) fulfill [5, 74, 75] ... 

In square-wave voltammetry of diffusion-controlled, reversible, and totally irreversible electrode reactions, the peak current is a linear function of the square root of frequency, but its relationship with square-wave amplitude is not linear. 

FIGURE 2.7 SQWV for microparticulate deposit of PY ion attached to zeolite Y deposited on paraffin-impregnated graphite electrode in contact with 0.10 M Et NClO /MeCN. Potential step increment, 4 mV square-wave amplitude, 25 mV frequency. 5 Hz. 

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