Voltammograms square-wave

Square-wave voltammogram reversible square-wave voltammogram, -> square-wave voltammetry... 

Potential-excitation signals and voltammograms for (a) normal pulse polarography, (b) differential pulse polarography, (c) staircase polarography, and (d) square-wave polarography. See text for an explanation of the symbols. Current is sampled at the time intervals indicated by the solid circles ( ). 

FIGURE 3-9 Square-wave voltammograms for reversible electron transfer. Curve A forward current. Curve B reverse current. Curve C net current. (Reproduced with permission from reference 9.)... 

Figure 3.8 Current-potential linear sweep voltammogram and the differential reflectivity change in the hydrogen adsorption region at fixed wavelengths (a) 2.34 pm and (b) 1.93 pm. The sweep rate was 15mVs with a square wave modulation of lOmV at 8.5 Hz. From Bewick et al.

After tq is passed, the second step starts by scanning the potential from Ed to a potential when all the deposited metals are re-oxidized (the reverse of reaction 25). The oxidation current recorded as a function of potential is the anodic stripping voltammogram (ASV). A typical ASY of three metals (Cd, Pb, and Cu) deposited on a mercury film electrode is shown in Fig. 18b.12b. The sensitivity of ASY can be improved by increasing the deposition time and by using the pulse technique to record the oxidation current. ASV in Fig. 18b. 12b was obtained by using the square wave voltammetry. In most cases a simple linear or step ramp is sufficient to measure sub-ppm level of metals in aqueous solution. The peak current of a linear scan ASV performed on a thin mercury film electrode is given by... 

Fig. 11 Square-wave (SW) voltammograms of [15] obtained (a) after adding about 1.6...

Fig. 27 Cyclic (top) and square wave (bottom) voltammograms of [55] (1.4 X 10 3 mol dm-3) recorded in CH2C12 at different scan rates and frequencies (in order of decreasing amplitude of current CVs 600, 400, 200, 100, 50, 20 mV s-1 ...

The potential perturbation in SWV is a stair-like square wave as shown in Fig. 64. Taking an average over time, the potential change in SWV can be considered as linear and the concept of scan rate still applies. In practice, the scan rate of an S W voltammogram is often described in terms of the frequency of the square wave, /, which can be converted to the scan rate by the following equation (see Fig. 64) ... 

Fig. 65 A square-wave voltammogram often observed for a highly reversible one-electron reduction in a non-aqueous solution.

As shown in Figure 42, the square wave voltammogram, as in DPV, is peak-shaped, but it consists of a differential curve between the current recorded in the forward half-cycle and the current recorded in the reverse half-cycle (pay attention to the fact that, since the forward and the reverse currents have opposite signs, their difference corresponds in absolute to their sum). 

Figure 24 Square wave voltammograms recorded at an edge-oriented pyrolytic graphite electrode in buffered aqueous solutions of [3Fe-4S] aconitase. (a) pH 6.2 (b) pH 7.5 (c) pH 8.2. Scan rate 0.1 V s ...

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... 

The spht net response may also appear if square-wave voltammogram of irreversible electrode reaction (1.1) is recorded starting from low potential, at which the reduction is diffusion controlled [22,23]. This is shown in Fig. 2.16b. If the starting potential is 0.3 V vs. E, a single net peak appears and the backward component of the response does not indicate the re-oxidation of the product (see Fig. 2.16a). If the reverse scan is applied (i st = —0.8 V, Fig. 2.16b), the forward, mainly oxidative component is in maximum at 0.190 V, while the backward, partly reductive... 

Fig. 2.14 Square-wave voltammograms for reduction of 1 mM Zn(II) in 1.0 M KNO3. AE = 5 mV, Esw = 25 mV. Experimental (...) and best fitting theoretical (-) currents with / in ascend-...

Fig. 2.15 Square-wave voltammogram collected at 10 Hz, background voltammogram subtracted.

Fig. 2.17a,b Square-wave voltammogram of Eu + (0.5 mmoldrn" ) in acidified 0.1 moldm NaC104 and its forward red) and backward blue) currents. Frequency 125 s amplitude 40 mV step potential 2 mV delay time 30 s scan direction negative (a) and positive (b) (reprinted from [23] with permission)... 

Fig. 2.51 Forward and reverse square-wave voltammograms of myoglobin-didodecyldimethyl-ammonium bromide films on a basal plane pyrolytic graphite eleetrodes at 200 Hz frequency, 10 mV step height, and different pulse heights. Points are experimental data, and lines are best fits by nonlinear regression onto the Mareus model. Baekground eurrents are ineluded in experimental and eomputed data. T = 37.0 0.2 °C, and the supporting eleetrolyte is 20 mmol/L pH 6.0 phthalate buffer +180 mmol/L NaCl (reprinted from [78] with permission)...

Fig. 2.68 Square-wave voltammogram of 5 x 10 mol/L SUDAN III solution recorded in a Ixuate buffer at pH = 10. The experimental conditions are itacc = —0.2 V, = 30 s, = 30 mV, / = 100 Hz and ML = 4 mV. Symbols 4, 4, and /net correspond to the cathodic, anodic and net current components of the SW response (reprinted from [91] Croat Chem Acta 76 37)...

Fig. 4 Square-wave voltammograms for Cg2 with a 610-mV potential gap between the second and third reductions. Reprinted with permission from Ref 58. Copyright 2000 Elsevier.

Fig. 20 DifFerential-pulse voltammogram of C121, (45) (a), square-wave voltammogram of C122H4, (44) (b), and Cgo (c) in o-dichlorobenzene with 0.1 M TBAP as supporting electrolyte. The first reduction potential of Cgo is shown by the dotted line. Reprinted with permission from Ref 152. Copyright 2001 American Chemical Society.

The usefulness of this kind of analysis is illustrated in Fig. 2.11 where the square wave voltammograms for azurite, smalt, and two samples from the frescoes painted by Palomino (1707) in the Sant Joan del Mercat church in Valencia (Spain) are shown. Copper pigments yield a unique stripping peak at —0.05 V, whereas cobalt pigments produce a main anodic peak at +0.02 V, accompanied by overlapping... 

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]...

---