Voltammetric probe

SECM-induced transfer [SECMIT Fig. 2(b)] can be used to characterize reversible phase transfer processes at a wide variety of interfaces. The basic idea is to perturb the process, initially at equilibrium, through local amperometry at the UME. Hitherto, diffusion-limited electrolysis has mainly been used in conjunction with metal tips, but ion transfer voltammetric probes (discussed briefly in Section III, and in detail in Chapter 15) can also be used. The application of a potential to the tip, sufficient to deplete the... 

The requirements for accurate recording of these two types of signals are quite different and lead to different equipment requirements. A sensitive potentiostat is required for a voltammetric probe and an electrometer is needed for a potentiometric probe. 

Daniele, S., Baldo, M.A., Ugo, P. and Mazzocchin, G.A. (1990) Voltammetric probe of milk samples by using a platinum microelectrode. Analytica Chimica Acta, 238, 357-366. Wojciechowski, M. and Balcerzak, J. (1991) Square-wave anodic-stripping voltammetry of lead and cadmium at cylindrical graphite fiber microelectrodes with in-situ plated mercury films. Analytica Chimica Acta, 249, 433-445. 

Fig. 3.22 a Pixel-by-pixel conelation between the electrochemical current map at potential 2 and the number of graphene layers, b Histograms of the electrochemical current and standard rate constant, if, for each defined number of CVD gnq>hene layers, for potentials Eu 2, and 3 (from left to right). The electrochemical oxidation of 2 mM FcTMA (30 mM KCl) is used as the voltammetric probe with 1, 2, and 3 corresponding to points on the voltammetric response of the FcTMA. The dashed line in (a) and the blue area in (b) denote the conditions where the electron transfer process becomes entirely reversible. Reprinted with permission from Ref. [39]. Copyright 2012 American Chemical Society... 

Daniele S, Baldo MA, Ugo P, Mazzocchin GA (1990) Voltammetric probe of milk samples by using a platinum microelectrode. Anal Chim Acta 238 357-366... 

Fig. 23.12 Standard version of the VIP system for in-situ monitoring and profiling, (a) Voltammetric probe, (b) multiparameter probe, and (c) online O2 removal system. Reproduced...

Tercier-Waeber ML, Buffle J, Confalonieri F, Riccardi G, Sina A, Graziottin F et al (1999) Submersible voltammetric probes for in situ real-time trace element measurements in surface water, groundwatea- and sediment-water interface. Meas Sci Technol 10 1202-1213... 

In the second category, SECMIT has been used to probe the relative permeability of oxygen between water and DCE or NB, with no supporting electrolyte present in any phase. Under the conditions employed, direct voltammetric measurements in the organic phase would be impractical due to the high solution resistivity (DCE or NB) or limitations of the solvent window available (NB). Figure 24 shows the steady-state current for the... 

As the electrochemical reaction is confined to the boundaries of the thin film, the voltammetric response exhibits a quasireversible maximum. The position of the quasireversible maximum on the log frequency axis depends on the kinetics of the overall reaction at the thin-film electrode, i.e., reflecting the coupled electron-ion transfer (4.3). Analyzing the evolution of the quasireversible maximum measured with different redox probes and various transferring ions, it has been demonstrated... 

DNA catalyzes the racemization of [Fe(phen)3] " "—the rate is approximately doubled in the presence of 1,000 pM DNA. DNA also shifts the A A equilibrium towards a slight enantiomeric excess of the A form. The electrostatic and intercalative interactions of [Fe(phen)3] + and [Fe(phen)3] " " with DNA have been probed voltammetrically, and binding constants estimated. The [Fe(phen)3f+-DNA interaction appears to be primarily electrostatic, [Fe(4,7-Ph2phen)2(phen)] -DNA interaction to be intercalative. The discussions in these recent publications suggest that early work on the kinetics and mechanism of racemization of [M(bipy)3]" and [M(phen)3] " ", M = Ni, Cr as well as Fe, is in danger of being overlooked or forgotten. Comparison of k and AH values for racemization and dissociation shows that racemization of... 

Pb UPD on Ag(lll) and Ag(lOO) has been studied using X-ray diffraction method, electrochemical impedance spectroscopy, and in situ scanning probe microscopy [272, 286-288]. This process has been reviewed in [265, 270], see Table 2. Both structure and voltammetric behavior are dependent on the Ag(h, k, 1) plane [265, 289]. 

The homogeneous catalysis method is suitable to measure rate constants over a very wide range, up to the diffusion limit. The lower limit is determined by interferences, such as convection, which occur at very slow scan rates. It is our experience that, unless special precautions are taken, scan rates below lOOmV/s result in significant deviations from a purely diffusion-controlled voltammetric wave. For small values of rate constants (down to 10 s ), other potentiostatic techniques are best suited, such as chronoamperometry at a rotating disk electrode UV dip probe and stopped-flow UV-vis techniques. ... 

The intercalation of polycyclic aromatic compounds into duplex DNA structures was used to develop nucleic acid-based electrochemical sensors.66 For example, the bis-ferrocene-tethered naphthalene diimide (16) was used as a redox-active intercalator to probe DNA hybridization.67 The thiolated probe was assembled on a Au electrode, and the formation of the duplex DNA with the complementary analyte nucleic acid was probed by the intercalation of (16) into the double-stranded nucleic acid structure and by following the voltammetric response of the ferrocene units (Fig. 12.17a). The method enabled the analysis of the target DNA with a sensitivity that corresponded to ca. 1 x 10-20mol. 

Two voltammetric techniques, stationary-electrode voltammetry (SEV) and cyclic voltammetry (CV), are among the most effective electroanalytical methods available for the mechanistic probing of redox systems. In part, the basis for their effectiveness is the capability for rapidly observing redox behavior over the entire potential range available. Since CV is an extension of SEV, many points pertinent to CV are discussed in the SEV section. 

The guanine redox activity of the target DNA was used to detect the duplex formation by carrying out a square-wave voltammetric measurement (SQW). The results of the parameters optimisation for the probe concentration (40 pg/ml), immobilisation time (5 min by applying a positive potential of +0.5V vs. Ag/AgCl pseudo reference electrode) and hybridisation time (10 min without any potential) were very similar to those obtained in previous work [3]. 

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