Fouling-resistant,polymer-modified graphite electrodes

Oxidation of several biochemically important phenols (phenol and tyrosine) and methoxyphenols (homovanillic acid, eugenol, vanillin and p-methoxyphenol) at spectroscopic graphite electrodes results in deactivation or fouling of the electrode surface. As has been previously well described, fouling is often due to the build-up of the oxidation products of these compounds at the electrode surface. Electrodes coated with gamma-irradiated immobilized films of poly(N-vinylpyrrolidone) do not exhibit the decrease in response with time observed at bare electrodes during the oxidation of these compounds. In some instances, this may be due to the structure of the polymer which may prevent large amounts of oxidation products from forming. In other instances, however, the nature of the products formed may differ at the coated electrodes. In this situation, responses as high as those initially obtained at bare electrodes may be obtained without the decrease in response as a function of time associated with bare electrodes.     

Recent advances in graphite powder-based electrodes

Graphite powder-based electrodes have the electrochemical performance of quasi-noble metal electrodes with intrinsic advantages related to the possibility of modification to enhance selectivity and their easily renewable surface, with no need for hazardous acids or bases for their cleaning. In contrast with commercial electrodes, for example screen-printed or sputtered-chip electrodes, graphite powder-based electrodes can also be fabricated in any laboratory with the form and characteristics desired. They are also readily modified with advanced materials, with relatively high reproducibility. All these characteristics make them a very interesting option for obtaining a large variety of electrodes to resolve different kinds of analytical problems. This review summarizes the state-of-the-art, advantages, and disadvantages of graphite powder-based electrodes in electrochemical analysis in the 21st century. It includes recent trends in carbon paste electrodes, devoting special attention to the use of emergent materials as new binders and to the development of other composite electrodes. The most recent advances in the use of graphite powder-modified sol–gel electrodes are also described. The development of sonogel–carbon electrodes and their use in electrochemical sensors and biosensors is included. These materials extend the possibilities of applications, especially for industrial technology-transfer purposes, and their development could affect not only electroanalytical green chemistry but other interesting areas also, for example catalysis and energy conversion and storage.     

Thick-film graphite electrodes in stripping voltammetry

Various types of modified thick-film graphite electrodes are reviewed. Two modification options are available: either in situ modified or beforehand. Electrodes modified in situ by various organic compounds were used for the determination of W, Mo, Cr, Ni and Mn by adsorptive stripping voltammetry. Insoluble inorganic salts, insoluble organic complexes or soluble compounds protected with Nafion were used for modification of the electrode surface beforehand. These pre-conditioned electrodes permit quantification of Pb, Cd, Cu, Zn, Sn, As and Hg ions. The detection limits of these elements were in the sub-μg/L range. The relative standard deviation did not exceed 10–15%. Measurements were made without deaeration of test solutions and normally without destroying small organic matter found in surface waters. A number of characteristics, such as the formation of well-shaped peaks and stable increments of peaks after standard additions, as well as elimination of the mechanical surface regeneration stage and metallic mercury or its soluble salts from the analytical procedure and a long shelf-life of the electrodes make them promising for electroanalysis and for application in portable field instruments. Received: 16 November 1998 / Revised: 16 February 1999 / Accepted: 20 February 1999     

Thick-film graphite electrodes in stripping voltammetry

Various types of modified thick-film graphite electrodes are reviewed. Two modification options are available: either in situ modified or beforehand. Electrodes modified in situ by various organic compounds were used for the determination of W, Mo, Cr, Ni and Mn by adsorptive stripping voltammetry. Insoluble inorganic salts, insoluble organic complexes or soluble compounds protected with Nafion were used for modification of the electrode surface beforehand. These pre-conditioned electrodes permit quantification of Pb, Cd, Cu, Zn, Sn, As and Hg ions. The detection limits of these elements were in the sub-μg/L range. The relative standard deviation did not exceed 10–15%. Measurements were made without deaeration of test solutions and normally without destroying small organic matter found in surface waters. A number of characteristics, such as the formation of well-shaped peaks and stable increments of peaks after standard additions, as well as elimination of the mechanical surface regeneration stage and metallic mercury or its soluble salts from the analytical procedure and a long shelf-life of the electrodes make them promising for electroanalysis and for application in portable field instruments. Received: 16 November 1998 / Revised: 16 February 1999 / Accepted: 20 February 1999     

Voltammetric studies with silicone rubber-based graphite electrodes

The behaviour of a new type of graphite electrode prepared by mixing spectral graphite with silicone rubber before cold vulcanisation, is described. Electrodes can be prepared as plates or rods. The residual current is reproducibly small or negligible in the potential range -0.3 V to +0.7V. The height of the peak current is proportional to the concentration for a wide range of substances. The reproducibility of i-E curves at the same electrode surface is excellent. The electrode requires no preliminary treatment and the surface can be easily cleaned or renewed. The temperature coefficient measured for hexacyanoferrate(II) was 1.1%/°C.     

Cu2+ ion-sensitive surface on graphite electrodes

Analytical and Bioanalytical Chemistry - A new electrochemical interface based on polyacrylic acid (PAAcid) immobilized in a Nafion® polymeric matrix on graphite screen-printed electrodes for...     

Improved electrooxidation of phenol at exfoliated graphite electrodes

In the presented paper, we report on electrochemical oxidation of phenol occurring at exfoliated graphite (EG) in alkaline solution. The mechanism of the electrocatalytic reaction of phenol oxidation was modified on adding methanol to the phenol-containing electrolyte. Using the voltammetry method, the influence of methanol additive on cyclic behavior of EG electrode was examined. A particular attention has been paid to the first two cycles when an abrupt decrease in electrocatalytic activity of various electrode materials has been observed. The results obtained showed that in the presence of methanol EG, electrode preserves its electrocatalytic activity for a longer time of phenol oxidation. In the absence of methanol in a phenol/KOH electrolyte, the charge of phenol oxidation peaks decreases sharply on cycling, whereas in the presence of methanol, the observed drop is considerably inhibited. The anodic charge attained for the 15th cycle of phenol oxidation in methanol-admixed electrolyte is the same as that for the third cycle recorded in methanol-free electrolyte. The thermogravimetric analysis (TG), Fourier-transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) data showed that an improved electrocatalytic activity of EG can be accounted for by new chemical composition of oligomer film built on the EG surface with the participation of methanol and/or the products of its oxidation.Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Electrooxidation of phenol by catalase immobilized on graphite electrodes

Electrocatalytic properties of catalase (CAT) immobilized on graphite and soot to mediate electrooxidation of phenol have been investigated. The kinetic parameters--Km, k(s), deltaG*Ar and Z0 of the process studied were calculated. Conclusions on a probable mechanism of the biocatalytic and electrochemical process observed were drawn from the calculated values of activation and kinetic parameters. A quantitative UV-spectrophotometrical approach was used as an analytical tool. The electrochemical oxidation of phenol was examined with potentiodynamic and polarization curves' method.     

Comparative immobilization of antibodies on modified screen-printed graphite electrodes

Immobilization of polyclonal antibodies was studied on native screen-printed graphite electrodes (SPEs) and variously modified electrodes. SPEs coated with didodecylammonium bromide (DDAB, a synthetic membranelike substance) films with gold nanoparticles gave the maximum electrochemical response. DDAB and gold nanoparticle films strongly changed the surface morphology, and the electrochemical signal became more intense and stable. This immobilization method increased the concentration of immobilized antibodies while their activity was retained. The detection limit of the enzymatic label (horseradish peroxidase) was 0.02 ng/L of sample.     

Potentiometric response of graphite electrodes coated with modified polymer films

Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10^?1–1 × 10^?5 M sodium thiocyanate.     

Direct electron transfer in immobilized flavoenzyme chemically modified graphite electrodes

Direct electron transfer between covalently immobilized flavoenzymes and a cyanuric chloride-modified graphite electrode is observed via differential pulse voltammetry. L-Amino acid oxidase and xanthine oxidase display peaks arising from the reduction of flavin adenine dinucleotide. Peak current enhancements are observed for both covalently attached enzymes compared to their free and adsorbed state voltammograms. Studies concerning flavin removal and reconstitution indicate that xanthine oxidase contains multiple flavin chromophores which are nonequivalent.     

Nickel oxide/expanded graphite nanocomposite electrodes for supercapacitor application

Nickel oxide/expanded graphite (NiO/EG) nanocomposites with different loading of EG were prepared through chemically depositing Ni(OH)₂ in EG followed by thermal annealing and characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) isotherm and electrochemical measurements. The prepared NiO/EG composites were found to be crystalline and highly porous with high specific surface area and pore volume. SEM analysis reveals uniform porous morphology for NiO in the NiO/EG-60 nanocomposites which shows good specific capacitance (510?F?g^?1) at a current density of 100?mA?g^?1 in 6?mol?L^?1 KOH measured by chronopotentiometry employing a three-electrode system. The specific capacitance retention of the NiO/EG-60 nanocomposites was found to be ca. 95% after 500 continuous galvanostatic charge–discharge cycles, indicating that the NiO/EG nanocomposites can become promising electro-active materials for supercapacitor application.     

Modification of platinum and graphite electrodes by cobalt hexacyanoferrate films

Methods for synthesizing cobalt hexacyanoferrate films on surfaces of the platinum and graphite electrodes are studied. The film properties depend on the modifying solution composition, including the nature of the supporting electrolyte cation, and the synthesis conditions. Reasons for the splitting of peaks in cyclic, voltammograms for the modified electrodes are put forth     

Voltammetric determination of morphine on stationary platinum and graphite electrodes

A voltammetric method for the determination of morphine in poppy seeds, crude morphine and pharmaceutical preparations is described. The method is based on electrochemical oxidation of morphine at a stationary graphite or platinum electrode in basic electrolyte. The mechanism of the electrochemical oxidation of morphine and its derivatives are discussed. The proposed method shows good reproducibility, and sample preparation is simple. The working ranges are 6 × 10^-5–10^-3 M with the graphite electrode and 10^-5–10^-3 M with the platinum electrode. There is no interference from various morphine derivatives or minor alkaloids at the 10^-3 M level.     

Electrocatalysis of redox reactions by metal nanoparticles on graphite electrodes

A selection of graphitic materials of both scientific as well as commercial importance has been modified by deposition of various metals at very low coverages under overpotential or underpotential conditions. Nanoparticles were found with some metals. The changes in the electrocatalytic activity of the supporting electrode by the metal modification were studied using electrochemical impedance measurements of a fast redox system. The carbon/solution interface was characterized with surface Raman spectroscopy, electrochemical impedance measurements, and cyclic voltammetry. Electronic Publication     

Amperometric enzyme sensor for glucose based on graphite paste-modified electrodes

Amperometric enzyme electrode for glucose is described based on the incorporation of glucose oxidase (GOD) into graphite paste modified with tetracyanoquinodimethane (TCNQ). The incorporated enzyme exhibits high activity and long-term stability over the earlier TCNQ-based glucose sensor (1). The sensor provides a linear response to glucose over a wide concentration range. The response time of the sensor is 15-50 sec, and the detection limit is 0.5 mM. Stable response to the substrate was obtained during a period of 35 d. Application of the sensor in the plasma analysis is reported.     

The properties of graphite electrodes modified by the quinone-hydroquinone system

The standard states of quinone and hydroquinone were selected to be those of pure substances, which allowed us to introduce the solubility product of quinhydrone. This selection of the standard state made it possible to interpret both the interval and direction of changes in the oxidation potential of graphite electrodes whose pores were filled by these substances in aqueous solutions with a fixed acidity.     

Recent developments on the modification of graphite electrodes with nanoparticles

The surface structure of common graphite electrodes are suitable for electrochemical detection of various analytes due to their favorable properties such as good conductivity and resistance to environmental and chemical hazards. Also this material is cheap and available. Modifying the surface of electrode improves their ability for various determinations. Modifying graphite electrodes with nanoparticles has attracted lots of attention due to their unique characteristics. In this article we review applications of modified graphite electrodes with nanomaterials.     

Electrochemical characterization of cobalt cordierites attached to paraffin-impregnated graphite electrodes

The electrochemistry of , and cobalt-containing cordierites (Co₂Al₄Si₅O₁₈) attached to paraffin-impregnated graphite electrodes has been studied by linear scan and cyclic voltammetries in HCl+NaCl and NaOH electrolytes. This electrochemistry is compared with that of vitreous cobalt cordierite, cobalt(II) oxide and cobalt spinel aluminate (CoAl₂O₄), the two last taken as reference materials. Electrochemical processes involve the site-characteristic reduction of Co(II) species to cobalt metal near to –0.5 V vs. SCE and their oxidative dissolution near +0.3 V, accompanied by solid state interconversion between Co(II) and Co(III) at potentials above +0.45 V. Cordierite-modified electrodes display a significant site-dependent catalytic effect on the electrochemical oxidation of mannitol in 0.10 M NaOH.     

Adsorption process of phenothiazine solution in dimethyl sulfoxide on graphite electrodes

In this paper, an original solution for the modeling and simulation of the adsorption process of a phenothiazine derivative on graphite electrodes is presented. The adsorption process is considered a distributed parameter one, due to the fact that the adsorbed phenothiazine quantity is a function depending on two independent variables. The structure parameters of the adsorption process, which define the influence of both independent variables, are determined using an experimental identification method. The experimental data are obtained through an experiment which is based on the process step response. In order to simulate the adsorption process, the approximate analytical solution, representing the process model, is determined. The simulation results prove the model generality; it is being simulated in relation to both independent variables.