Microelectrode cyclic voltammogram

Figure 3.98 Comparison of a reversible conventional cyclic voltammogram (linear diffusion) and reversible steady-state voltammogram obtained at a single microelectrode disc where mass transport is solely by radial diffusion. Current axis not drawn to scale. From A.M. Bond and H.A.O. Hill, Metal Inns in Biological Systems, 27 (1991) 431. Reprinted by courtesy of Marcel...

Figure 5. Generation/collection experiment with poly(I)-coated microelectrodes in CH3CN/O.I M [n-Bu4N]PFg at 10 mV/s. The lower cyclic voltammograms are for the generator electrode as its potential is swept between -0.2 V and -0.9 V vs. Ag+/Ag while the potential of the collector electrodes is held at 0.0 V vs. Ag+/Ag.

Cyclic voltammograms of PtSn microelectrodes in 0.5 M sulfuric acid solution are shown in Fig. 15.6. The potential range was -200 to 800 mV (vs. SCE) and the scan rate was 100 mV/s. It can be seen clearly that hydrogen desorption from the PtSn-2 electrode is seriously inhibited compared with that from the PtSn-1 electrode. From the hydrogen desorption peak areas in the CV curves and the Pt single crystallite hydrogen desorption constant of 210 /xC/cm Pt, the electrochemical surface areas (ESA) for PtSn-1 and PtSn-2 were calculated to be 391 and 49 cm /mg, respectively. However, it is evident from XRD and TEM results that the two catalysts have similar particle size and so they should possess the similar physical surface area. The difference... 

A novel application of ionic liquids in biochemistry involved duplex DNA as the anion and polyether-decorated transition metal complexes. When the undiluted liquid DNA-or molten salt-is interrogated electrochemically by a microelectrode, the molten salts exhibit cyclic voltammograms due to the physical diffusion (D-PHYS) of the polyether-transition metal complex. These DNA molten salts constitute a new class of materials whose properties can be controlled by nucleic acid sequence and that can be interrogated in undiluted form on microelectrode arrays (Leone et al., 2001). 

Cyclic voltammetric and related techniques are particularly valuable for determining Ea values in cases where one member of the redox couple is unstable. At a microelectrode in electrolytes of low resistivity, cyclic voltammograms can be recorded at scan rates up to about 100 V s-1 and at low temperatures. This allows the detection of reversibility when the unstable partner has a life-time of the order of a millisecond or so. Ultra-microelectrode techniques promise to lower this limit even further.1-3... 

Figure 16.5 Variable-temperature cyclic voltammograms (50 mV/s) recorded at 10-(left panel) and 25-pm (right panel) Pt microelectrodes for 2 mM Cp Fe in 0.2 M Bu4NPF6, 1 2 butyronitrile ethyl chloride. [Reprinted with permission from S. Ching, J.T. McDevitt, S.R. Peck, and R.W. Murray, J. Electrochem. Soc. 735 2308 (1991). Copyright 1991 The Electrochemical Society, Inc.]...

Figure 9 shows a cyclic voltammogram (CV) of hexacyanoferrate(III) (Fe(III)) in water observed at a gold microelectrode (8 fim wide x 33 fim long x 0.2 fim thick). A cathodic current at 200 mV corresponds to reduction of Fe(III) to Fe(II). At a micrometer-sized electrode, mass transfer of a solute in water to the electrode proceeds very efficiently owing to hemispherical diffusion of the solute. This is proved by a characteristic sigmoidal current-potential curve in the CV, different from a peak current observed at a millimeter-size electrode (linear diffusion) [32,64]. Using... 

Another example of a transient array is the set of microelectrodes on which cyclic voltammograms are recorded and a suitable pattern recognition technique is used to analyze it. Clearly, the boundaries of information acquisition can be greatly expanded by the inclusion of time and by careful analysis of the transient signals. 

Figures 8.7a and b show cyclic voltammograms obtained on the skin with a platinum microelectrode and with a gold microelectrode, respectively. The shape of the current-potential curves was different.

Fig. 8.8. Cyclic voltammograms obtained (a) with a platinum microelectrode in a deaerated phosphate buffer solution (—) or in a deaerated ascorbic acid ImmolL-1 and uric acid lmmolLT1 solution (—) and (b) with a gold microelectrode in a deaerated phosphate buffer solution (—) or in a deaerated glutathione ImmolL-1 solution (—). Potential scan rate 50mVs-1.

Cyclic voltammograms were also performed with platinum microelectrodes on skin surface at regular time intervals of about 7 h. Figure 8.10 shows the typical curve giving the evolution of the anodic current at 0.9V/SCE as a function of time. A sinusoidal evolution was observed for the nine volunteers. Current values as well as the amplitude and the period of the variations were different for each subject. It has been verified that the amplitude of the current variations was significantly higher than the accuracy of the amperometric response. Consequently, the variation of the anodic current was actually due to a variation of the oxido-reductive properties of the skin and was not an artifact of the measurements. 

Fig. 8.2. Cyclic voltammogram performed with a 50-pm diameter platinum microelectrode in a deaerated 5 mmol L-1 Fe(CN) solution (pH 7.0). Potential scan rate 50 mV s-1.

In order to study the physiologic evolution of the redox properties of skin, cyclic voltammograms are performed with platinum microelectrodes, every 15 min over 7 h. Each measurement was realized with a new microelectrode. For this preclinical study, nine volunteer subjects were involved they remained relaxed in the same room and their diet was checked during the whole experiment. 

For more than 300 platinum microelectrodes produced, the average metallic wire radius is 30 + 3 pm (i.e. an accuracy of 10%). This value is coherent with the wire radius commercially indicated and shows the good repeatability of microelectrodes fabrication. In addition, more than 100 reproducible cyclic voltammograms can be recorded successively in the ferricyanide solution without modification of the curve shape. 

Cyclic voltammograms cannot be recorded in the two non-conductive creams whatever the electrode material used, even when using platinum microelectrodes. 

Figure 4.4 Cyclic voltammograms (continuous lines) obtained for a 20 pm radius mercury microelectrode immersed in a 10 pM solution of 20H-AQ in 1.0 M HCIO4. The scan rates, from top to bottom, are 50, 20, 10 and 5 V s the current scale is on the right-hand side. The dotted line represents the cyclic voltammogram observed for the same electrode immersed in a 10 mM solution of 20H-AQ in this case, the scan rate is 50 V s, with the current scale on the left-hand side. In all cases, cathodic currents are up, and anodic currents are down, with the initial potential being +0.250 V. Reprinted with permission from R.J. Forster, Anal. Chem., 68, 3143 (1996). Copyright (1996) American Chemical Society...

Figure 5.3 Cyclic voltammogram of a spontaneously adsorbed [Os(bpy)2py(p3p)]2+ monolayer, obtained by using a scan rate of 50 V s 1, with a surface coverage of 9.5 x 10 n mol cnr2. The supporting electrolyte is 0.1 M TBABF4 in acetonitrile, and the radius of the platinum microelectrode is 25 xm. The cathodic currents are shown as up, while the anodic currents are shown as down. The complex is in the [Os(bpy)2py(p3p)]2+ form between +0.400 and —1.200 V the initial potential was 1.000 V. Reprinted with permission from R. J. Forster, Inorg. Chem., 35, 3394 (1996). Copyright (1996) American Chemical Society...

Figure 5.27 Cyclic voltammograms obtained for 30 pm radius mercury microelectrodes immersed in 5 pM solutions of (a) adriamycin and (b) quinizarin. The scan rates are, from top to bottom, 50,20, 10 and 5 V s-1 the supporting electrolyte is 1.0 M HC104. The cathodic currents are shown as up, while the anodic currents are shown as down the initial potential is —0.700 V. From R. J. Forster, Analyst, 121, 733 - 741 (1996). Reproduced by permission of The Royal Society of Chemistry...

Fig. 14.34. Voltammetry of epinephrine. Background (A, solid line) and signal containing (A, dashed line) currents generated during fast-scan cyclic voltammetry (300 V/s) at a carbon fiber microelectrode r = 5 pm). A background subtracted cyclic voltammogram (B) is produced from the traces shown in A. (Reprinted from Wightman, et al. Chemical Communication, Interface, 5(3) 22, Fig. 2,1996. Reproduced by permission of the Electrochemical Society, Inc.)...

Fig. 11.8 Cyclic voltammograms for the oxidation of 5 mM ferrocene in [C4mim][PF6] on a platinum microelectrode (diameter 10 j.m) at lOOmVs 1. Reference electrode was a Pt wire inserted into [C4mim][PF6]...

Fig. 11.10 Cyclic voltammograms for (a) the reduction of 12.5 mM benzoquinone (BQ) in [C4mim][NTf2] on a platinum microelectrode (diameter 10 am) at lOOmVs 1 and (b) the oxidation of20mM Af/SfNfN -tetramethylphenylenediamine (TMPD) in [C4dmim][NTf2] on a platinum electrode (diameter 10 J.m) at 4Vs-1.

Fig. 9.8. Cyclic voltammograms at a microelectrode, (a) Low scan rate (—0.1 V s-1) (b) High scan rate (>10 V s 1). Note the similarity with hydrodynamic electrodes.

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