Polarogram differential pulse

Differential pulse polarograms for the oxidation of R4Pb (R = Ph, Me, Et, Bu) in CH2C12 on DME all show an electrode response for oxidation. This DPP response is, however, spread over a wide potential range of 300 mV indicating that several processes are reflected by this wave. The DPP responses for several lead compounds are cited in Table 6. 

Figure 6.25 Differential pulse polarogram of I0 mol dm" in hydrochloric acid (0.01 mol dm ) at a DME. The separation in potential, A , during the pulse was —50 mV. Note that the y-axis here is not current but differential current. Reproduced from Greef, R., Peat, R., Peter, L.M., Pletcher, D. and Robinson, J., Instrumental Methods in Electrochemistry, Ellis Horwood, Chichester, 1990, with permission of Professor D. Pletcher, Department of Chemistry, University of Southampton, Southampton, UK.

Figure 4. Cyclic voltammogram and differential pulse polarogram of electrodes prepared as in Fig. 2, spectrum E. Recorded using solution conditions from Fig. 3. The differential pulse polarogram was recorded with a scan rate of 2 mV/s.

Figure 3.6 Potential-time sequence for (a) normal-pulse polarogram and (b) differential-pulse polarogram. The current-time response for the latter is given by (c), with fi and f3 the times at which current is measured, t2 the time at which pulse is applied, and r4 the time at which pulse is removed.

Figure 23-20 (a) Differential pulse polarogram 0.36 ppm tetracycline-HCl in 0.1 M acetate buffer, pH 4, PAR Model 174 polarographic analyzer, DME, 50-mV pulse amplitude, 1-s drop, (b) DC polarogram 180 ppm tetracycline-HCl in 0.1 M acetate buffer, pH 4, similar conditions. (Reprinted with permission from J. B. Plato, Ana/. Chem., 1972,44, 75A. Published 1972, American Chemical Society.)... 

Figure 5. Polarogram (d.c.) (left) and differential-pulse polarogram (right) of 2.4 x 10" M methanearsonic acid in CHjOH-0.1 M guanidinium perchlorate. Drop time, 0.5 s pulse width,...

Figure 6. Polarogram (d.c.) (left) and differential-pulse polarogram (right) of reduction of (h -CjHj)jCo in 1,2-dimethoxyethane with phenol added. The waves owing to reduction of (h -CjH jCo and h -CjHjCoCjHj-h are labeled. Drop oscillations are not shown in the d.c. polarogram. [Reproduced with permission from W. Geiger, W. Bowden, N. El Murr, Inorg. Chem., 18. 2358 (1979).]...

Figure 1. Various electrochemical techniques applied to study of reduction of two isomers of (h -CgHglCoCjHj-h From top, d.c. polarogram. cyclic voltammogram, differential-pulse polarogram, a.c. polarogram ( > = 1256 s ). The DPP and a.c. plots are obtained with a different reference electrode and are displaced ca. 60 mV positive.

Figure 6 in 12.3.2.1.2 shows d.c. and differential-pulse polarograms for this system. The DPP data are used to calculate a rate constant for protonation of the cobaltocene anion. Cobalt carboranes undergo similar ECE processes and CV scans show waves owing to protonation products at negative potentials . 

Figure 6. Polarogram (d.c.) (left) and differential-pulse polarogram (right) of reduction of...

Fig. 98. Differential pulse polarograms (b) of NAD and methylviologen (MV) at an anaerobic flat Hg electrode (a) covered with a GOD-catalase membrane. (Redrawn from Scheller et al., 1987a).

Differential pulse polarography also produces an ambiguous record for this kind of situation, as shown in Figure 7.3.18c. A peak is seen only for the Cd " reduction, because the trace covers potentials only on the negative side of the Fe wave. We note again that the differential pulse polarogram approximates the derivative of the normal pulse record hence distinct peaks will not be seen in DPV (or in SWV) unless distinct waves appear in NPV. 

Figure 7.3.19 Differential pulse polarogram for a mixture of tetracycline and chloramphenicol. AE = — 25 mV. [From Application Note AN-111, EG G Princeton Applied Research, Princeton, NJ, with permission.]...

Fig. 21. Differential pulse polarogram of 7.3 dinitroestriol, 0.1 M phosphate buffer. (From Wehmeyer et al., 1982, with permission.)...

Fig. 24. Plot of normalized peak current [(peak current)/(concentration DNE)] from differential pulse polarograms of 5.0 ml of phosphate buffer solution containing dinitroestriol (DNE), bovine IgG, estriol, and (or) estrogen-specific antisera. O, DNE 7.0 xM plus bovine IgG as shown on bottom scale A, DNE 7.0 jlA1 plus bovine IgG (0.7 g/liter) and estriol (74 jxM) , DNE 8.8 iM plus bovine IgG (0.3 g/liter) and estrogen-specific antisera as shown on top scale , DNE 8.8 pM plus bovine IgG (0.3 g/liter), estrogen-specific estriol (0.9 g/liter), and estriol (6.0 pM). (From Wehmeyer et al., 1982, with permission.)...

The peak shape of differential-pulse polarograms results from the relation... 

Figure 15.33 Effect of standard additions on a differential pulse polarogram.

Record a differential pulse polarogram of a background electrolyte without and with added tapwater. Which metal species are present Use a standard additions calibration to quantify one of the metal impurities. Compare Upeak with 1/2,. ... 

Figure 15. Differential pulse polarograms of cytochrome c at various concentrations in 0.10 M Tris-cacodylate buffer, pH 6.05, and 0.10 M sodium perchlorate. Adapted from Reference (102) with permission.

Figure 17. Effect of pH variation on (A) the differential pulse polarograms and (B) on the 695 nm absorbance band of 114/xM cytochrome c. Solution contained mixed 0.01 M Tris-cacodylate and 0.10 M sodium perchlorate buffer/electrolyte. For a series of solution pH values, 6.4, 7.0, 7.6, 8.2, and 9.5, the arrows indicate the direction of change in the responses with increasing pH. Adapted from Reference (102) with permission.

Fig.3. Differential pulse polarograms of 0.1 mM glycerol trinitrate in water/methanol solutions, using 0.1 M ammonium acetate electrolyte. Methanol content a = 20 %, b = 40 %, c = 60 % and d = 80 %.

The composition of the solvent has an essential influence on the reversibility of the electrode reaction. From an analytical point of view, solvents giving reversible electrode reactions are to be preferred. The form of a differential pulse polarogram is dependent on the composition of the solution, which in turn will have an influence on the possibilty of getting a successful multi-component determination. As an example, the differential pulse polarograms for glycerol trinitrate (Fig.3) and 2,4,6-trinitrotoluene (Fig.4) in water/methanol solutions, are shown. 0.1 M ammonium acetate is used as the electrolyte. 

Fig.6. Differential pulse polarograms of 0.1 mM 2,4,6-trinitrotoluene in 60 % methanol, using a) 0.1 M ammonium acetate, b) 0.1 M tetram-ethyl ammonium bromide electrolyte.

To demonstrate the influence of buffered and non-buffered solutions differential pulse polarograms of glycerol trinitrate and 2,4,6-trinitrotoluene, are shown in Fig.5 and 6 respectively. The electrolytes are 60 % methanol solution with 0.1 M ammonium acetate (buffered solution) and 0.1 M tetramethyl ammonium bromide (non-buffered solution) electrolytes. 

Using differential pulse polarography, it is possible to analyse mixtures of several electroactive compounds with completely or partially overlapping polarograms, provided that the analytical conditions can be chosen in such a way that sufficiently large differents in the differential pulse polarograms can be achieved for the different compounds. 

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