Activation of glassy carbon electrodes by alternating current electrochemical treatment

Glassy carbon electrodes subjected to “severe” electrochemical treatment is saturated chloride solutions exhibit enhanced electrochemical reversibility compared to untreated electrodes. Apparently faster rates of electron-transfer result in lowering of the overpotential by 110–300 mV for eight electroactive species tested. Systematic alterations in the response in terms of peak potential, sensitivity, background current, and stability are reported. Scanning electron micrographs show the introduction of pits of random size distribution. From the practical point of view, the most significant improvement is observed in differential pulse measurements, that are highly sensitive to small changes in the rate of electron transfer. In amperometric detection for liquid chromatography, the pretreated electrodes are shown to facilitate the quantitation of different eluting species. It appears that the surface and bulk properties of the glassy carbon have profound effects on the observed behavior.     

Surface preparation of glassy carbon electrodes

Recent work on glassy carbon electrodes for various applications is reviewed. Activation of glassy carbon electrodes by different types of polishing, heat treatment, and electrochemical methods yields enhanced rates of electron transfer. Characterization of different glassy carbon surfaces by x-ray photoelectron spectroscopy shows that polished and electrochemically pretreated surfaces contain more oxygen on the surface than do unactivated surfaces; much of this oxygen is associated with phenolic groups. Causes of activation, characterization of glassy carbon by spectroscopic methods, and the role of surface cleanliness are summarized. For simple electron-transfer reactions, removal of contaminants from the electrode surface is important. For proton-coupled electrode reactions, specific interactions of reactants with catalytic groups created on the surface during polishing tend to play an important role in electrode activation     

Electrochemical oxidation and determination of ceftriaxone on a glassy carbon and carbon-nanotube-modified glassy carbon electrodes

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10⁻⁶ cm² s⁻¹. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10⁻⁶ M with the proposed method.     

Evaluation of mercury coated glassy carbon electrodes for oscillographic polarography

The suitability of a mercury film electrode formed over a glassy carbon substrate for oscillographic polarography has been studied. The data obtained show that it is possible to get well-developed oscillograms characteristic of the depolariser (in the concentration range 10^∮5–3×10^?4M) in solution which are similar to those obtained with a dropping mercury electrode. For quantitative analysis the mercury film electrode has been found to have limited applicability since the indentations have been found to be time-dependent.     

Sonoelectroanalysis: investigation of bismuth-film-modified glassy carbon electrodes

Bismuth-modified glassy carbon electrodes have been investigated for their suitability in sonoelectroanalysis. The stability of the bismuth film to the application of ultrasound was assessed via voltammetric and atomic force microscopy (AFM) studies which revealed little ablation at powers up to an intensity of 130 W cm^–2 delivered from a 25-kHz sonic horn. Furthermore, bismuth-film-modified glassy carbon electrodes were evaluated for the sonoelectroanalytical quantification of zinc and cadmium. Detection limits of 2×10^–7 M and 6×10^–9 M respectively were found after a 60-s deposition time via an acoustically assisted deposition protocol.     

Surface topography of anodically treated glassy carbon electrodes

Flat-topped mesas are formed on glassy carbon surfaces as a result of electrochemical oxidative treatment in aqueous sodium hydroxide. The topography of the anodically exposed glassy carbon was followed by phase detection interferometric microscopy. The appearance and the distribution of the mesas were found to be related to the mode of electrochemical treatment. A threshold time, a function of applied voltage, and a threshold voltage for the formation of the mesas were found. In addition, the physical size and number of the structures increased with applied voltage.     

Perfluoro anion-exchange polymeric films on glassy carbon electrodes

Solutions of the perfluoro anion-exchange membrane TosHex® in a solvent mixture composed of methanol + isopropanol + water (1:1:1) were prepared and applied in coating glassy carbon electrodes. The evaporated films were used to accumulate the Fe(CN) ₆ redox couple on the electrode surface. The magnitude of the electrochemical response of the loaded films is comparable with that for Nafion® incorporated cationic redox species. The multicharged Fe(CN) ₆ couple accumulated in Tosflex® film causes an ion cross-linking of the polymeric backbone, thus decreasing ion transport in the film substantially.     

Permselectivity of neurotransmitters at overoxidized polypyrrole-film-coated glassy carbon electrodes

The permselectivity of neurotransmitters such as dopamine, epinephrine, and norepinephrine at overoxidized polypyrrole (OPPY)-film-coated glassy carbon electrodes has been investigated. The chemically-modified electrodes exhibit attractive permselectivity and antifouling properties of rejecting anionic species, e.g. ascorbate, etc. Compared with the response of neurotransmitters at modified electrodes overoxidized in phosphate buffer solution (pH 7.4), higher sensitivity and reversibility response can be obtained at modified electrodes overoxidized in sodium hydroxide solution. The effect of film thickness on the permselective response was tested. Rotating disk electrode experiments were used to determine the apparent diffusion coefficients of several electroactive solutes in the OPPY films. The influence of the hydrophobicity of the organic ions on the permeability within the polymer films was discussed. Dopamine and epinephrine were determined at the 1 x 10(-6)-1 x 10(-4) M level by means of voltammetry after an exposure period of 2 min in 0.1 M phosphate buffer (pH 7.4) with detection limits of 8 x 10(-7) M and 6 x 10(-7) M respectively.     

Electrochemical behaviour of platinum at polymer-modified glassy carbon electrodes

In this paper, the preparations and voltammetric characteristics of chitosan-modified glassy carbon (Ct-MGC) and platinum electrodes are studied. Ct-MGC can be used for pre-concentration and quantification of trace amounts of platinum in solution. At low pH medium, the complex of Pt with protonated group-NH³⁺ in the chitosan molecule has been confirmed by FT-IR spectra studies.     

Direct electrochemistry of catalase on glassy carbon electrodes.

Catalase was investigated as a possible catalyst of the electrochemical reduction of oxygen on glassy carbon electrodes. The presence of catalase dissolved in solution only provoked a moderate current increase, which was fully explained by the catalase-catalysed disproportionation of hydrogen peroxide (Scheme I). When catalase was adsorbed from dimethylsulfoxide on the surface of electrodes that did not undergo any electrochemical pre-treatment (EP), catalase efficiently catalysed oxygen reduction via direct electron transfer from the electrode (Scheme II). The results are discussed with respect to the electrode surface properties and the enzyme structure.     

纳米金修饰玻碳电极对儿茶酚的催化氧化

研究了电沉积纳米金修饰玻碳电极对儿茶酚的催化氧化,发现该修饰电极使儿茶酚的氧化电位大大降低,峰电流显著增大并且线性范围较宽;讨论了酸度、沉积量、扫速等条件对儿茶酚在纳米金修饰玻碳电极上催化氧化的影响。该电极制备简单,重现性好,用于儿茶酚的定量分析,发现儿茶酚氧化峰电流与浓度在2.0×10-6~1.2×10-2mol/L范围内呈良好的线性关系,相关系数为0.9965,检出限(3σ)为3.2×10-7mol/L;用于样品检测,效果较好。     

Site-specific voltage control of adsorption on glassy carbon electrodes

The influence of applied potential on the adsorption of organic compounds on glassy carbon (GC) electrodes has been examined using electrochemically modulated liquid chromatography (EMLC). The results not only confirm that the extent of adsorption is site dependent [Anal. Chem. 69 (1997) 4680], but also demonstrate for the first time that these sites exhibit differences in their potential dependence of adsorption. The results additionally reveal how the extent of adsorption is affected by the supporting electrolyte. Together, these results demonstrate the power of EMLC to serve as a tool for unraveling fundamental issues regarding adsorption on carbonaceous and other electrified interfaces.     

Oxygen reduction on carbon nanomaterial-modified glassy carbon electrodes in alkaline solution

Electroreduction of oxygen in alkaline solution on glassy carbon (GC) electrodes modified with different carbon nanomaterials has been studied. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode and rotating ring-disk electrode methods. The GC disk electrodes were modified with carbon nanomaterials using polytetrafluoroethylene as a binder. Four different carbon nanomaterials were used: multiwalled carbon nanotubes, carbon black powder, and two carbide-derived carbons (CDC). For the first time, the electrocatalytic behavior of CDC materials toward oxygen reduction is explored. Electrochemical characterization of the materials showed that all the carbon nanomaterial-modified GC electrodes are highly active for the reduction of oxygen in alkaline solutions.     

Bioelectrochemical studies on catalase modified glassy carbon paste electrodes

The enzyme catalase (EC: 1.11.1.6) has been covalently coupled onto the surface of glassy carbon (GC) powder matrix using a 16 atom spacer arm. The enzyme coupled powder was made into a paste electrode that was used to study the electrochemical properties. Standard electrochemical techniques like cyclic voltammetry, differential pulse voltammetry and flow injection analysis studies were carried out using this paste electrode. The cyclic voltammogram of the modified paste exhibited a clear increase in the reduction peak at −180 mV in the presence of hydrogen peroxide. The potential at which maximum Faradaic activity was observed was determined using differential pulse voltammetry, which showed a clear peak at −100 mV. This potential was used to monitor the response of the electrode to varying substrate concentrations using a home made setup for flow injection analysis. A linear increase in the current values in the range 0.1–1 mM hydrogen peroxide concentration was observed in our system.     

Carbon-nanotube-modified glassy carbon electrodes for amplified label-free electrochemical detection of DNA hybridization

The preparation and attractive performance of carbon-nanotube modified glassy-carbon (CNT/GC) electrodes for improved detection of purines, nucleic acids, and DNA hybridization are described. The surface-confined multiwall carbon-nanotube (MWCNT) facilitates the adsorptive accumulation of the guanine nucleobase and greatly enhances its oxidation signal. The advantages of CNT/GC electrodes are illustrated from comparison to the common unmodified glassy carbon, carbon paste and graphite pencil electrodes. The dramatic amplification of the guanine signal has been combined with a label-free electrical detection of DNA hybridization. Factors influencing the enhancement of the guanine signal are assessed and optimized. The performance characteristics of the amplified label-free electrochemical detection of DNA hybridization are reported in connection to measurements of nucleic-acid segments related to the breast-cancer BRCA1 gene.     

Electrochemical parameters of ethamsylate at multi-walled carbon nanotube modified glassy carbon electrodes

In this paper, some electrochemical parameters of ethamsylate at a multi-walled carbon nanotube modified glassy carbon electrode, such as the charge number, exchange current density, standard heterogeneous rate constant and diffusion coefficient, were measured by cyclic voltammetry, chronoamperometry and chronocoulometry. The modified electrode exhibits good promotion of the electrochemical reaction of ethamsylate and increases the standard heterogeneous rate constant of ethamsylate greatly. The differential pulse voltammetry responses of ethamsylate were linearly dependent on its concentrations in a range from 2.0 x 10(-6) to 6.0 x 10(-5) mol L(-1), with a detection limit of 4.0 x 10(-7) mol L(-1).     

Direct electrochemical conversion of bilirubin oxidase at carbon nanotube-modified glassy carbon electrodes

We report on direct electron transfer reactions of bilirubin oxidase at multi-walled carbon nanotube (MWCNT) modified glassy carbon electrodes (GCE). The bioelectrocatalytic oxygen reduction was recorded using linear sweep voltammetry (LSV) with BOD in solution, adsorbed and covalently linked to the nanotubes. The MWCNT modification of GC electrodes strongly enhances the oxygen reduction compared to the signals at unmodified GCE. Under anaerobic conditions with a high protein concentration in solution a pair of redox peaks with a formal potential of 450 ± 15 mV vs Ag/AgCl, 1 M KCl (pH 7.4) was found with cyclic voltammetry. The redox conversion is indicated to be surface-controlled and pH-dependent (54.5 mV/pH). The quasi-reversible redox reaction might be attributed to the trinuclear T2/T3 cluster of BOD.     

Characterization of mediated and non-mediated oxidase enzyme based glassy carbon electrodes

The performance and analytical characteristics of a glassy carbon glutaraldehyde immobilized glucose oxidase electrode have been established with regard to the direct detection of hydrogen peroxide produced from the reaction of glucose with oxygen. Measurements were performed at + 1.1 V vs. SCE, and selectivity was obtained by casting the surface with a cellulose acetate membrane. Results compared favorably with the classical platinum-enzyme probe. The mechanism of ascorbic acid interference in hydrogen peroxide detection is reported. Mediated detection was also investigated for oxidase enzymes (glucose oxidase and xanthine oxidase) immobilized on the bare glassy carbon electrode. The probes were characterized using a specific enzyme mediator in solution (phenazine methosulfate or dichlorophenol-indophenol) plus hexacyanoferrate(III) as an electrochemical mediator. The electrode was poised at + 0.36 V vs. SCE for the detection of hexacyanoferrate(II). The advantages of this dual mediator configuration include high stability and sensitivity of the electrochemical signal and the ability to use less positive potentials for increased selectivity. Application to other enzymes, such as hydrogenases, using such a binary redox configuration is suggested.