Voltamogram

In some cases the cyclic voltamogram itself recorded when ramping the electrode potential as described above shows a characteristic minimum around iipzc (e.g. with single crystal gold electrodes [86Kol, 96Ham2]) (Data obtained with this method are labelled CV). 

CS = coulostatic method, CV = cyclic voltamogram, FD = Faradaic distortion method, FR = Faradaic rectification, GD = galvanostatic double pulse method, IP = impedance method, PS = potential step method. See also list of... 

Figure 7.1 Cyclic voltamograms of Pt(l 11) electrodes modified by Bi, Sb, As, and Te deposition at intermediate coverages, as indicated, in 0.5 M H2SO4 solution. Sweep rate 50 mV/s.

Complexes with pyridine-2,6-diimine ligands, five-coordinate [NiX2(174)] (X = C1, Br) or six-coordinate [Ni(174)2]X2, were usually assumed to have innocent neutral ligands. The X-ray structure and spectroscopic characteristics of [Ni(174)2](PF6) confirm that the complex contains the neutral ligand ([174] ) and a divalent nickel ion.579 The cyclic voltamogram of this complex in CH2C12 shows three reversible one-electron-transfer processes at = 1.19 V, —1.30 V, and — 1.82V (vs. Fc+/Fc), of which the first is a one-electron oxidation, while the other two correspond to two successive one-electron reductions. The spectroscopic data allow one to assign these processes as follows ([174]1 is a one-electron reduced radical form of [174] ) [Nini(174)°2]3+ [NiII(174)02]21 - " [NiI(174)°2]+ = " [NiI(174)°(174)1 ]°. 

To further identify the electro-oxidation products of 1 , the C. V. of 1 and I3 were also recorded. There are similarities and dissimilarities in the cyclic voltamogram. While (Ep) = 0.690 V is same in both the C.V. s, there is another anodic peak at 1,054 mV (absent in the r - e 1 case) for the same concentration of 1-and two corresponding cathodic peaks at 787 and 406 mV as compared to that of 1. It was also noted that the anodic peak in the case of [1] = 0.5 mM was quite sharp manifesting a two-electron oxidation. It is not so in the case of I3. Thus recombination I.to form Ij, followed by the reaction of 1 with (excess) 1 in solution to form 1 and oxidation of 1 is not involved in the electro-oxidation of 1. 

A cyclic voltamogram of a saturated solution of 1 shows an anodic peak at 637 mV (scanning upto 1,000 mV) and two cathodic peaks at 615 and 316 mV. None of them at the position of the anodic/cathodic peak in C.V of oxidation of T. To further identify the electro-oxidation product of 1 Eq. 27.5, cyclic voltammogram of 1 at low concentration of I was rerecorded. For [T] <0.5 mM there is only one... 

The formal electrode potentials of diynyl complexes are greatly influenced by the nature of the other supporting ligands (Table V). For example, the cyclic voltamograms (CVs) of the iron complexes Fe(C=CC=CSiMe3)(CO)2(/ -C5R5)... 

Low temperature cyclic voltammetry is also able to demonstrate reduction of the individual rotamers of 2,3-dibromobutane [115]. At room temperature when there is fast bond rotation, reduction proceeds through the conformation with trans-periplanar arrangement of carbon-bromine bonds. At -120° C, a second peak at more negative potentials appears in the cyclic voltamogram, due to elimination from tlie staggered arrangement of carbon-bromine bonds. 

The value A Ef = —35.6 mV has the particular interest of corresponding to a 50 % of character E e-E c and E2c At the average formal potential Ef, the intermediate species reaches half of its maximum value and, hence, at this A Ef species 02 may or may not gain a second electron (and as a direct consequence, for higher AEf it will be considered that the intermediate species is no more stable at the average formal potential). So, this AEf could be considered as the boundary between anti-cooperative and cooperative behavior of both electron transfer reactions [35, 43]. Indeed, it is well known that the voltamogram of an EE mechanism under these conditions is identical to that of an E mechanism multiplied by a factor... 

Reversibility has not been demonstrated and the shape of the voltamogram seems to allow the possibility of a (C4H9)4N + mediated process even at Pt. 

G. K. Rowe, M. T. Carter, J. Richardson, and R. W. Murray, Langmuir 11 1797 (1995). Obtaining electrode kinetic parameters from cyclic voltamograms involving proteins. 

T. M. Nahir, R. A. Clark, andE. F. Bowden, Anal. Chem. 66 2595 (1996). Linear sweep voltamograms with cytochrome c adsorbed on SAMs. 

The detection of (specifically) dopamine is hindered by the presence in the extracellular fluid of several compounds having redox potentials close to that of dopamine. The technique most likely to succeed here is fast scan cyclic voltammetry (Section 8.6) because the voltamogram provides characteristics that are indicative of the individual compound being monitored. The microelectrodes used have radii of 5 pm, but even this is not small enough to be able to determine dopamine from just one cell. The reacting compounds come from several nerve endings. Nevertheless, the fast scan cyclic voltammetry technique her sufficient time and resolution to allow information to be obtained on the part played by dopamine in neurotransmission in the brain. For example, it answers such questions as does the released dopamine stay at the synapse or does it diffuse in the extracellular fluid to contact other neurons ... 

Figure 9. Cyclic voltamograms for 1.0 x 10 M ascorbic acid (A), uric acid (B), dopamine...

Figure 32. (a) Cyclic voltamograms of a platinum electrode coated with a [Ni(4-TRPyP)] [PFg]4 film,... 

Figure 2 Cyclic voltamograms for (a) ferrocene [Fe(Cp)2] (Cp = cyclopentadienyl anion, measured in CH3CN with 0.1 M...

The selectivity inherent to electrochemical detection is derived from the differences between the oxidation or reduction half-wave potentials exhibited by different analytes. Even when two or more analytes have nearly the same half-wave potentials, complexing agents or alterations in mobile-phase composition can be used to differentiate between analytes. In order to carry out the electrochemical quantitation of an analyte, the potential difference between the working microelectrode and the reference electrode is maintained at a value that lies on the plateau of the oxidation or reduction wave (voltamogram) of the analyte of interest. The diffusion current thus measured, which is due to the oxidation or reduction of the analyte, is proportional to the area under the analyte peak eluted. In order for absolute quantitation to be effected, the diffusion current of a standard sample of the analyte must also be measured for comparison with that of the unknown sample. 

Os(IlI) solution at pH 3.1 contains an Os "OH species, whereas Os(lV) solutions at the same pH have an Os 0 species. From Pourbaix diagram we see that Os "OH complex remains protonated in the pH range 3.1 to 13. This means that at very high sweep rates electron transfer is going to be fast in comparison to proton transfer. As a consequence we should see one reversible peak in the cyclic voltamograms in this pH range. 

E8.25 (a) If Os(IV) complex decomposed rapidly, then the voltamogram would not be reversible, and would be... 

Figure 20.3 Polarographic cell and diffusion current. The solution must be free from dissolved oxygen which otherwise causes an interfering double wave (see Figure 20.6). On the right, graph of the diffusion current, growing over time for each drop of mercury in a static solution (unstirred solution). Direct polarography is a slow method of analysis. The recording of a voltamogram requires at least one hundred droplets. A calculation of % max is possible with the Ilkovic equation if the coefficient 607 is replaced by 706 in equation 20.2.

Because of zinc s high electronegativity, this element must have participated in some manner with the corrosion processes. About the only possible indications from the electrochemical and x-ray evaluations made, are the small reduction peaks observed at about — 1.15 V for protein solutions on the 5 V/min cyclic voltamograms. These cathodic peaks for use as evidence in showing zinc corrosion may just as well be reduction of copper products, since cathodic peaks are shifted negatively with respect to their redox potentials at faster sweep rates. 

Figure 2 Cyclic voltamograms for (a) ferrocene [Fe(Cp)2] (Cp = cyclopentadienyl anion, CsHs ) measured in CH3CN with O.iM BU4NPF6 dispiaying a reversible oxidation at 0.43 V versus SCE and (b) [Rh "(bpy)3] (bpy = 2,2 -bipyridine), an example of an irreversible reduction followed by two reversible reductions measured in CH3CN with 0.1 M Et4NC104 versus SCE. (Reprinted with permission from Kew, DeArmond, and Hanck 1974 American Chemical Society)...

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