Glassy carbon electrode, activated

Fig. 5.78. SR spectra of a glassy carbon electrode activated electrochemically before (—) and after decoration with silver in contact with an aqueous solution of 0.1 M K2SO4, open circuit electrode potential, Laser = 514.5 nm, Pq = 100 mW, resolution 2 cm" (based on data in [354])...

Glassy carbon electrodes polished with alumina and sonicated under clean conditions show activation for the ferrl-/ ferro-cyanlde couple and the oxidation of ascorbic acid. Heterogeneous rate constants for the ferrl-/ ferro-cyanlde couple are dependent on the quality of the water used to prepare the electrolyte solutions. For the highest purity solutions, the rate constants approach those measured on platinum. The linear scan voltammetrlc peak potential for ascorbic acid shifts 390 mV when electrodes are activated. 

Such reduction In overpotentlal Is the largest observed for a bare glassy carbon electrode. The presence of surface qulnones may be Indicative of activation but does not appear to mediate the heterogeneous electron transfer. XFS results support the presence of qulnones as a minor constituent on the surface. 

The purpose of this paper Is 1) to describe the electrochemistry of ferrl-/ferro-cyanlde and the oxidation of ascorbic at an activated glassy carbon electrode which Is prepared by polishing the surface with alumina and followed only by thorough sonlcatlon 2) to describe experimental criteria used to bench-mark the presence of an activated electrode surface and 3) to present a preliminary description of the mechanism of the activation. The latter results from a synergistic Interpretation of the chemical, electrochemical and surface spectroscopic probes of the activated surface. Although the porous layer may be Important, Its role will be considered elsewhere. 

Figure 1. The redox behavior of I,4-dlhydrobenzene at a deactivated versus various activated glassy carbon electrodes.

Figure 2. Cyclic voltammograms of ferrl-/ ferro-cyanlde couple at an activated glassy carbon electrode at scan rates of a) 20, b) 50, and c) 100 mV s . See text for details.

Figure 3. Cyclic voltammograms of ascorbic acid at a freshly polished, active (a) and a deactivated (b) glassy carbon electrode surface. See text for details.

Figure 17.12 Direct electrocatal3ftic oxidation of D-fnictose at a glassy carbon electrode painted with a paste of Ketjen black particles modified with D-fructose dehydrogenase from a Gluconobacter species. The enzyme incorporates an additional heme center allowing direct electron transfer from the electrode to the flavin active site. Cyclic voltammograms were recorded at a scan rate of 20 mV s and at 25 + 2 °C and pH 5.0. Reproduced by permission of the PCCP Owner Societies, from Kamitaka et al., 2007.

Detection of damage caused to DNA by niclosamide in schistosomiasis was investigated using an electrochemical DNA-biosensor. It showed for the first time clear evidence of interaction of niclosamide with DNA and suggested that niclosamide toxicity can be caused by this interaction, after reductive activation. The electrochemical reduction and oxidation of niclosamide involved the use of cyclic, differential, and square-wave voltammetry, at a glassy carbon electrode. It enabled the detection limit of 8 x 10-7 M [34]. 

Based on IgG-bearing beads, a chemiluminescent immuno-biochip has been also realized for the model detection of human IgG. Biotin-labeled antihuman IgG were used in a competitive assay, in conjunction with peroxidase labelled streptavidin59. In that case, the planar glassy carbon electrode served only as a support for the sensing layer since the light signal came from the biocatalytic activity of horseradish peroxidase. Free antigen could then be detected with a detection limit of 25 pg (108 molecules) and up to 15 ng. 

A. Salimi, A. Noorbakhsh, and M. Ghadermarz, Direct electrochemistry and electrocatalytic activity of catalase incorporated onto multiwall carbon nanotubes-modified glassy carbon electrode. Anal. Biochem. 344,16-24 (2005). 

Other techniques that have been used include subtractive differential pulse voltammetry at twin gold electrodes [492], anodic stripping voltammetry using glassy-carbon electrodes [495,496], X-ray fluorescence analysis [493], and neutron activation analysis [494],... 

A recent study (1) has demonstrated that the electrochemical oxidation of hydroxide ion yields hydroxyl radical ( OH) and its anion (O"-). These species in turn are stabilized at glassy carbon electrodes by transition-metal ions via the formation of metal-oxygen covalent bonds (unpaired d electron with unpaired p electron of -OH and O- ). The coinage metals (Cu, Ag, and Au), which are used as oxygen activation catalysts for several industrial processes (e.g., Ag/02 for production of ethylene oxide) (2-10), have an unpaired electron (d10s1 or d9s2 valence-... 

The electro-oxidation of organics and more specifically of alcohols and polyols is also possible on silver electrodes in the following activity sequence methanol < ethylene glycol < glycerol [64]. With a bulk silver electrode and with a silver-modified glassy carbon electrode, oxidations proceed only in the area of silver oxide formation. 

A polypyrrole film electrochemically deposited on gold electrodes from an MeCN-liCl04/Co(OAc)2 solution shows electrocatalytic activity in dioxygen reduction [404]. The catalytic electroreduction of dithio dipropionic acid (PSSP) with the water-soluhle cohalt(II I)tetrakis(4-trimethyl-ammonium phenyl) porphyrin (CoTMAP) has heen studied. The Co catalyst adsorbed on the glassy carbon electrode plays a major role in the electroreductive cleavage of the S—S bond [405]. 

An aluminum electrode modified by a chemically deposited palladium pen-tacyanonitrosylferrate film was reported in [33]. Vitreous carbon electrode modified with cobalt phthalocyanine was used in [34]. Electrocatalytic activity of nanos-tructured polymeric tetraruthenated porphyrin film was studied in [35]. Codeposition of Pt nanoparticles and Fe(III) species on glassy-carbon electrode resulted in significant catalytic activity in nitrite oxidation [36]. It was shown that the pho-tocatalytic oxidation at a Ti02/Ti film electrode can be electrochemically promoted [37]. 

Fig. 12 Cyclic voltammogram of [Mn202(phen)4] + in pH 4.5 phosphate buffer at an activated glassy carbon electrode i = 0.1 V s (reprinted with permission from Ref 97, Copyright 1992 American Chemical Society).

The voltammetric reduction of a series of dialkyl and arylalkyl disulfides has recently been studied in detail, in DMF/0.1 M TBAP at the glassy carbon electrode The ET kinetics was analyzed after addition of 1 equivalent of acetic acid to avoid father-son reactions, such as self-protonation or nucleophilic attack on the starting disulfide by the most reactive RS anion. Father-son reactions have the consequence of lowering the electron consumption from the expected two-electron stoichiometry. Addition of a suitable acid results in the protonation of active nucleophiles or bases. The peak potentials for the irreversible voltammetric reduction of disulfides are strongly dependent on the nature of the groups bonded to the sulfur atoms. Table 11 summarizes some relevant electrochemical data. These results indicate that the initial ET controls the electrode kinetics. In addition, the decrease of the normalized peak current and the corresponding increase of the peak width when v increases, point to a potential dependence of a, as discussed thoroughly in Section 2. 

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