Modified Graphite Electrode Research Articles

A comparative study of different adenine derivatives for the electrocatalytic oxidation of β-nicotinamide adenine dinucleotide

The electrochemical oxidation of the adenine moiety in different adenine derivatives, including adenosine, adenosinemonophosphate (AMP), adenosinediphosphate (ADP) and adenosinetriphosphate (ATP), has been studied at pyrolytic graphite electrodes in aqueous solution in the pH range 5–11. All these compounds yield strongly adsorbed electroactive oxidation products with reversible behavior and formal potentials close to 0 V at pH 9.0. These oxidation products show strong electrocatalytic activity for the oxidation of the reduced form of β-nicotinamide adenine dinucleotide (NADH). The electrochemical properties of the electrocatalyst obtained by oxidation of the corresponding parent nucleotide were investigated by cyclic voltammetry. The influence of the structure of the parent compound on the electrocatalytic activity of the corresponding product toward NADH oxidation was studied also. The kinetics of the electrocatalytic reactions were evaluated from rotating disk electrode measurements. These modified graphite electrodes can be used as NADH transducers in biosensors for substrates of dehydrogenase enzymes and also for the measurement of enzymatic activity.

Surface-modified electrodes for NADH oxidation in oxidoreductase-catalysed synthesis

Three surface-modified electrodes were investigated: 3,4-dihydroxybenzaldehyde electropolymerized on glassy carbon, hexacyanoferrate modified nickel electrodes, Meldola Blue adsorbed on graphite, for application to NADH oxidation in oxidoreductase-catalysed synthesis. The high overpotential, which is generally required for NADH oxidation on clean electrodes, was perfectly overcome with the three electrodes and especially with the Meldola blue modified graphite electrode. This electrode allowed fast NADH oxidation at potentials as low as 0.00 V vs SCE. It also ensured good storage stability. It is stressed that the key problem in applying this electrode to synthesis is the decrease in its electrocatalytic properties under operating synthesis conditions. An operating procedure was established that allowed ageing of the electrode to be directly linked to the current measurement. Following this procedure, several methods were investigated for improving the half-life of the electrode: pulse electrolysis, replacing NADH by NAD+ in the initial solution, lowering the NAD+ concentration and using dextran-bound NAD+. In the best conditions, the half-life reached 152 min instead of 34 min with the initial conditions, proving that fouling by anodically produced NAD+ was first of all identified as a very important cause of electrode ageing. Modification of intrinsic surface properties of the electrode also led to the decrease of the interface efficiency.

Electrooxidation mechanism of biogenic amines at amine oxidase modified graphite electrode.

Amine oxidase (AO, EC. 1.4.3.6) was previously shown to be a very efficient biological recognition element of amperometric biosensors for monitoring biogenic amines. The enzyme was effectively working in both mono- and bienzyme electrode designs, based on either a direct or a mediated electron-transfer pathway. This work focuses on the elucidation of the electron-transfer mechanism of the monoenzymatic unmediated AO-modified biosensor. The observed unmediated catalytic currents were assumed to be caused by (i) a direct electron-transfer process, (ii) the electrooxidation of the formed product, or (iii) their combination. Experiments supporting these assumptions are discussed in detail.

Amperometric Biosensor for Hydrogen Peroxide Based on Immobilization of Horseradish Peroxidase on Methylene Blue Modified Graphite Electrode

A methylene blue modified graphite electrode was first prepared by adsorbing the molecules on a spectrographic graphite disk electrode saturated with wax. Then, a novel hydrogen peroxide biosensor was fabricated based on immobilization of horseradish peroxidase on the methylene blue modified graphite electrode by cross-linking with glutaraldehyde. This electrode exhibited excellent electrochemical activity in aqueous solutions, and the electron transfer rate constant for the adsorbed methylene blue was determined as 0.12 s–1. It was demonstrated that the modified methylene blue molecules could shuttle electrons between immobilized HRP and graphite substrate very well for H2O2 sensing. The characteristics of this sensor were evaluated with respect to applied potential, pH and temperature. A detection limit of 3.0×10–6 mol/L hydrogen peroxide was examined at simple experimental conditions. Dopamine and ascorbic acid did not interfere with the determination. This sensor was also stable, reproducible and outstanding for long-term use.

Chemically modified sensor for amperometric determination of sulphur dioxide

Copper hexacyanoferrate (CuHCF) modified graphite electrode prepared by mechanical immobilisation method has been used for the amperometric determination of sulphite, which can be extended for the determination of SO 2 in air after absorbing the pollutant in sodium hydroxide solution. This method is based upon the electrocatalytic oxidation of sulphite by the modified electrode. The pH of the medium for oxidation should be in the range of 3.5–8.0. The range of determination of SO 2 is from 5.1 to 30.7 ppm. The presence of H 2S with SO 2 will interfere in the determination. This can be eliminated by precipitating H 2S as CuS.

Voltammetric Response of a γ-Irradiated Poly(N-vinylcaprolactam) Modified Graphite Electrode to Catechol and Ascorbic Acid

Voltammetric Response of a γ-Irradiated Poly(N-vinylcaprolactam) Modified Graphite Electrode to Catechol and Ascorbic Acid

Electrocatalytic Oxidation of NADH in Flow Analysis by Graphite Electrode Modified with 2,6-Dichlorophenolindophenol Salts

The preparation of a 2,6-dichlorophenolindophenol (DCPI) modified graphite electrode is described. DCPI was successfully immobilized by physical adsorption onto a plain graphite electrode (DCPI-CME) and onto graphite electrodes pretreated with lanthanum nitrate (DCPI-La-CME) or thorium nitrate (DCPI-Th-CME). The electrochemical behavior of DCPI-CME was extensively studied using cyclic voltammetry. The electrochemical redox reaction of DCPI was found to be fairly reversible at low coverage with Eo′ = +55 mV (vs. Ag/AgCl/3M KCl) at pH 6.5. A pKa value of 5.8 ± 0.1 for immobilized form of DCPI is determined from the intersection of the lines in the plot Eo′ vs. pH. The current Ip has a linear relationship with the scan rate up to 1200 mV s−1, which is indicative for very fast electron transfer kinetics. The calculated value of the standard rate constant is ko = 18 ± 4 s−1. No decrease of either the anodic or the cathodic current of the cyclic voltammogram was observed after 500 runs of successive sweeps. The influence of the morphology of the electrode surface on the electrochemical behavior of the DCPI-CME was studied and a mathematical model is proposed, which partly describes the dependence of the geometrical area of the electrode surface on the grid of the emery paper. The modified electrodes were mounted in a flow-injection manifold, poised at +60 mV (vs. Ag/AgCl/3M KCl) and a catalytic current due to the oxidation of NADH was observed reducing thus the oxidation overpotential of NADH for about 400 mV. Interference from various reductive species present in real samples was investigated. The repeatability was 1.2 % RSD (n = 10 for 0.1 mM NADH). The sensor showed good operational and storage stability.

Comparison of rotating disk and wall-jet electrode systems for studying the kinetics of direct and mediated electron transfer for horseradish peroxidase on a graphite electrode

Abstract This paper presents a comparison between the results obtained for the kinetics of direct and mediated electroreduction of hydrogen peroxide at horseradish peroxidase (HRP) modified graphite electrodes, used either as a rotating disk electrode (RDE) or as the working electrode in a wall-jet flow through cell. The advantages of using a wall-jet flow system compared with a RDE system for kinetic investigations are that there is no need to account for substrate consumption, especially in the case of desorption of enzyme, and also when studying product-inhibited enzymes. The comparison reveals that identical results can be obtained using either technique. The ratio of HRP molecules on the graphite surface in direct electron transfer contact was determined as 48±4%, and the turnover number of the heterogeneous electron transfer between adsorbed HRP and the graphite electrode was determined as 1.9±0.3 s −1 .

Os(bpy)2(PVP)10Cl]Cl polymer and Nafion dual-film modified graphite electrode for the amperometric determination of trace amounts of norepinephrine.

A chemically modified graphite electrode was prepared by using a dual film of [Os(bpy)2(PVP)10Cl]Cl polymer and Nafion. The modified electrode showed excellent electrocatalytical activity for the oxidation of norepinephrine (NE) and an ability to eliminate efficiently the interference of ascorbic acid and other anions. The catalytic peak currents obtained from the cyclic voltammograms increased linearly with increasing concentration of NE. A log-log plot of catalytic current versus NE concentration showed a dual-linear relationship in the ranges 1.8 x 10(-8)-4.4 x 10(-6) M and 4.4 x 10(-6)-2.9 x 10(-4) M with correlation coefficients of 0.990 and 0.999, respectively. The detection limit was about 18 nM (3 delta). At a potential of +500 mV the chronoamperometric response showed a linear relationship between the steady state current and NE concentration in the range 1.3-130 microM. With a further increase in NE concentration a Michaelis-Menten-shaped response was observed. The apparent Michaelis-Menten constant and the maximum current were 1.7 mM and 86 microA, respectively. The modified electrode showed excellent reproducibility, sensitivity and stability for the determination of NE at trace levels.

Self-gelatinizable copolymer immobilized glucose biosensor based on Prussian Blue modified graphite electrode†

A novel poly(vinyl alcohol) grafting 4-vinylpyridine self-gelatinizable copolymer was adapted to immobilize glucose oxidase. The reduction of hydrogen peroxide (H2O2) was detected at a Prussian Blue (PB) modified graphite electrode. A stable and sensitive glucose amperometric biosensor is described. The copolymer is a good biocompatible polymer in which the glucose oxidase retains high activity. Moreover, the copolymer can adhere firmly to the inorganic PB membrane. The sensor showed an apparent Michaelis-Menten constant of 18 +/- 0.2 mM and a maximum current density of 1.14 microA cm-2 mM-1. The linear range is from 5 microM to 4.5 mM glucose and the detection limit is 0.5 microM glucose. The catalytic efficiency of PB for the reduction of H2O2 is higher than that for the oxidation of H2O2. Glucose concentrations in serum samples from healthy persons and diabetic patients were determined using the sensor. The results compared well with those provided by the hospital using a spectroscopy method.

Disposable thick film modified graphite electrodes for stripping voltammetry

Disposable thick film modified graphite electrodes (DTFMGE) are described. Disposable thick film graphite electrodes (DTFGE) are used as a substrate for DTFMGEs. Insoluble inorganic mercury salt, organic insoluble complexes or soluble compounds protected with Nafion were used to modify electrode surface. That provides the possibility to determine Pb, Cd, Cu ions concentration without using metallic mercury and its soluble salts and to eliminate the need for mechanical surface regeneration. As to their characteristics, these electrodes differ little from the usual ones which are coated with mercury either beforehand or in situ. Test concentrations of Me 2+ were: 1 μg 1 −1 Cd( II) + 2.0 μg 1 −1 Pb( II) + 5 μg 1 −1 Cu( II) in one series of the experiments, 2 μg 1 −1 Cd( II) + 4.0 μg 1 −1 Pb( II) in the second series and 10 μg1 −1 Cd( II) + 10 μg 1 −1 Pb + 10 μg1 −1 Cu( II) in the third series. Two additions were injected into electrochemical cell. The detection limit for the elements mentioned is on the sub-μg 1 −1 level. Relative standard deviation is 2–5%. 0.1, 0.2 and 1 M HCl were used as background electrolytes. Results were obtained without deaeration of the solution. Well shaped peaks, stable peak increments after standard additions introduction and satisfactory correlation between added and found concentrations of metal ions during a long period of time makes the electrodes promising prospective for stripping voltammetry.

Analytical applications of graphite electrode modified with Bis(diisopropyloxithiophosphon)Disulphide

A modified graphite electrode was produced by adsorption the bis(diisopropyloxythiophosphone)disulphide {(i-PrO-) 2P(S)S-} 2 under vacuum. Its electrochemical characteristics in flowing stream were described. The modified electrode has been used for simultaneous determination of Cu(II), Ag(I) by flow injection anodic stripping voltammetry.

Highly sensitive determination of hydrogen peroxide and peroxidase with tetrathiafulvalene-based electrodes and the application in immunosensing

Redox mediators enable an efficient electron transfer between redox enzymes and the electrochemical surface of amperometric sensors. A stable and highly sensitive signal was obtained using a tetrathiafulvalene (TTF)-modified graphite electrode. In the presence of horseradish peroxidase (HRP), hydrogen peroxide (H 2O 2) was monitored with a detection limit of 7 nM at a potential of +20mV versus a saturated calomel electrode (SCE). With a constant concentration of H 2O 2, the detection limit for HRP was found to be 150 pM. The accuracy of consecutive measurement of HRP in flow-through systems was improved by short-time polarizing the TTF-modified graphite electrode at + 100 mV versus Ag/AgCl/3 M KCl. Using the TTF-modified graphite electrode in an immuno-sandwich approach, rabbit-immunoglobulin G was monitored in the range 5–100 ng/ml.

Electrocatalytic CO 2 reduction by cobalt octabutoxyphthalocyanine coated on graphite electrode

Electrocatalytic CO 2 reduction was studied by using a modified graphite electrode coated with cobalt octabutoxyphthalocyanine (CoPc(BuO) 8) and dipped in an aqueous electrolyte. The CoPc(BuO) 8 worked as a catalyst to produce CO with higher activity and selectivity than the non-substituted CoPc. Under typical conditions at pH 4.4, the most active and selective CO 2 reduction was achieved at −1.30 V with turnover number of the catalyst ∼ 1.1 × 10 6 h −1 and the selectivity of the produced CO H 2 ∼ 4.2 . The high activity was ascribed to the electron-donating BuO substituents of the complex, which would facilitate the coordination of CO 2 as well as the electron transfer from the complex to the coordinated CO 2 molecule. The use of a poly(4-vinylpyridine) membrane to disperse the complex decreased the activity. The mechanism was investigated by the use of in situ potential-step chronoamperospectroscopy (PSCAS) in a homogeneous CoPc(BuO) 8/pyridine solution. In the absence of CO 2, distinct two-steps visible spectral changes were observed following the first and second reductions of the complex. However, under CO 2 atmosphere, only the one-electron reduced species was present under steady state. It was proposed that the third reduction of a CO 2-coordinated CoPc(BuO) 8 should take place for CO production.

Factors affecting selective electrocatalytic co 2 reduction with cobalt phthalocyanine incorporated in a polyvinylpyridine membrane coated on a graphite electrode

Electrocatalytic CO 2 reduction was carried out using a modified graphite electrode coated with a poly(4-vinylpyridine) (PVP) membrane containing cobalt phthalocyanine (CoPc). In a typical electrolysis in a 0.1 M NaH 2PO 4 aqueous phase (pH 4.4), the catalyst membrane achieved a much more selective CO 2 reduction than that by a neat CoPc coating. The degree of the selectivity, defined as the ratio of CO to H 2 produced, was about 6 at .20V vs. Ag¦AgCl. The catalytic activity of CoPc was ascribed to the properties of PVP which is co-ordinative and weakly basic. Important factors affecting the CO 2 reduction were investigated, such as applied potential, pH and CoPc concentration in the membrane. An optimum applied potential of −1.20V vs. Ag¦AgCl was found for selective CO production. As for the pH, an optimum condition was obtained at pH ≈ 5 where the PVP provides a partially protonated environment around the CoPc. The CO/H 2 selectivity was strongly dependent on the CoPc concentration in the membrane ([CoPc] PVP) especially at lower applied potentials; higher [CoPc] PVP brings about higher CO/H 2 selectivity. As for the effects of PVP, coordination of the pyridine group to CoPc as well as the microenvironment around CoPc provided by the polymer were concluded as dominant factors. A concerted protonation-deprotonation mechanism for the CO production process assisted by partially protonated PVP species was suggested. From the voltammetric and in situ potential-step chronoamperospectroscopy measurement, it was proposed that the CoPc/CO 2 intermediate accepts a third electron to produce CO.

Carbon electrodes in amine analysis: Effect of chemically modified carbon surfaces on signal quality and reproducibility

AbstractThe preparation of chemically modified graphite electrodes by various chemical treatments is described. These electrodes were tested with chlorpromazine, cyclopiroxolamine, sulfathiazole, bamipine, sparteine and diphenhydramine by differential pulse voltammetry. Compared with the unmodified and freshly polished carbon electrodes, the modified ones exhibit attractive properties such as enhanced stability against film formation. The initial signals at untreated electrodes are very high and decrease rapidly, but at pretreated electrodes the stability of the signals is usually improved. Adsorption and poisoning by film formation is suppressed by giving the surface of the electrode a chemical identity by chemical pretreatment. The improvements are not general but individual ones.

Asymmetric Reduction of Acetophenone Using L-Valine Methyl Ester Modified Graphite Electrode

Asymmetric Reduction of Acetophenone Using L-Valine Methyl Ester Modified Graphite Electrode

Electrocatalytic activity of a graphite electrode coated with hexadecachlorophthalocyanatoiron(II) toward sulfide oxidation, and its possible application in electroanalysis

A graphite electrode coated with hexadecachlorophthalocyanatoiron(II), FeII[Cl16Pc(2-)], serves as an electrocatalyst for the oxidation of sulfide ion in basic solutions (pH range: 8–14). The surface electrochemical responses of this catalyst and corresponding electrocatalytic activity are discussed. The sulfide ion concentration dependences of the peak current in cyclic voltammograms are examined to show the possible application of this catalyst-coated electrode in amperometric sulfide sensors. Keywords: phthalocyanine, modified graphite electrode, sulfide oxidation, electroanalysis, electrocatalysis.

Electron transport in biological procesess II: Electrochemical behaviour of Q 10 immersed in a phospholipidic matrix added on a pyrolitic graphite electrode

In order to study the behaviour of ubiquinone inside a phospholipid matrix, the E-pH diagrams for CoQ 10 adsorbed on a graphite electrode and on a phospholipid modified graphite electrode were compared. The stabilization area for the protonated free radical HQ was found to be larger in the presence of phospholipids, contrary to results obtained for the charged species. This fact strongly supports the role proposed for ubiquinone in the respiratory chain model where a stable neutral semiubiquinone radical would allow the unitary electron transport through the inner mitochondrial membrane.

Direct bioelectrocatalytic reduction of hydrogen peroxide at chloroperoxidase modified graphite electrode

The electroreduction of hydrogen peroxide was studied at a chloroperoxidase-modified graphite electrode. The reduction of H2O2 starts at more negative potentials than 0.45 V versus SCE at pH 7.0. The steady-state reduction currents are greater at acidic pH values, and in the presence of chloride ions in solution. The apparent Michaelis–Menten constant and sensitivity were evaluated to be equal to 105 µmol l–1 and 1.3 mA l mol–1 for the electrode responses to the H2O2 in 0.1 mol l–1 phosphate buffer solution free of chloride ions. On the basis of these results direct electron transfer is postulated between the active site of chloroperoxidase and the graphite electrode.