Electrochemical self-assembly of nordihydroguaiaretic acid/Nafion modified electrodes and their electrocatalytic properties for catecholamines and ascorbic acid

Electrochemically active 1,4-bis(3,4-dihydroxyphenyl)-2,3-dimethylbutane (nordihydroguaiaretic acid, NDGA) films can be directly deposited on Nafion modified electrodes from aqueous nordihydroguaiaretic acid. The deposited NDGA/Nafion films are stable, and show obvious electrochemical activity in aqueous solutions with various pH. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of the NDGA/Nafion films. When freshly prepared NDGA/Nafion films were transferred to aqueous solutions at various pH, the formal potential was found to be pH dependent. The NDGA/Nafion films electrocatalytically oxidized dopamine, epinephrine, and norepinephrine in aqueous solutions, with the electrocatalytic oxidation current developing through the oxidized form of the NDGA/Nafion film. NDGA/Nafion films also showed reversible electrocatalytic properties. Such films electrocatalytically reduce the oxidation products of dopamine, epinephrine, and norepinephrine resulting from the electrocatalytic oxidation of these compounds by the NDGA/Nafion film. The NDGA/Nafion modified films also electrocatalytically oxidized a mixture of dopamine and ascorbic acid. The chemical reaction of dopamine quinone with ascorbic acid was investigated using the rotating ring-disk electrode method.     

Characterization and electrocatalytic properties of cobalt hexacyanoferrate films immobilized on Au-colloid modified gold electrodes

An electroactive cobalt hexacyanoferrate (CoHCF) film was electrodeposited from a solution containing Co²⁺ and Fe(CN)₆^3? ions on the bare gold or the Au-colloid modified electrode. The cation (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺) and the anion (F^?, Cl^? and Br^?) effects on the redox peak of the CoHCF film were investigated in detail. On the other hand, the electrocatalytic oxidations of thiosulfate at the CoHCF/gold and CoHCF/Au-colloid/gold electrodes were compared. At the CoHCF/Au-colloid/gold electrode, we obtained a response current larger by a factor of 2 and a three times lower detection limit than those at a CoHCF/gold electrode. The linear ranges were 1.0 × 10^?4 to 2.8 × 10^?3 M for the CoHCF/gold electrode and 7.5 × 10^?5 to 4.8 × 10^?3 M for the CoHCF/Au-colloid/gold electrode. These results showed that the immobilized CoHCF at the Au-colloid modified electrode exhibited a higher catalytic activity and a wider linear range toward thiosulfate. Additionally, the effects of the applied potential and the solution pH were studied.     

Electrocatalytic characteristics of ascorbic acid oxidation at nickel plated aluminum electrodes modified with nickel pentacyanonitrosylferrate films

Nickel pentacyanonitrosylferrate (NiPCNF) films have been deposited on the surface of an aluminum electrode by a simple electroless dipping method. The cyclic voltammogram of the resulting surface modified Al electrode prepared under optimum conditions, shows a well-behaved redox couple due to the [Ni^IIFe^III/II(CN)₅NO]^0/?1 system. The NiPCNF films, formed on the Al electrode show excellent electrocatalytic activity towards the oxidation of ascorbic acid in phosphate buffer solution of pH 7.2. A linear calibration graph is obtained over the ascorbic acid concentration range 2–50 mM using linear sweep voltammetry. The kinetics of the catalytic reaction were investigated using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The rate constants for the catalytic reaction evaluated by three different approaches, are in good agreement and were found to be around 10^?3 cm s^?1. Further examination of the modified electrodes shows that the modifying layers (NiPCNF) on the aluminum substrate have reproducible behavior and a high level of stability.     

UV/ozone pretreatment of glassy carbon electrodes

A commercial UV/ozone cleaning device is investigated for use in pretreating glassy-carbon (GC) electrodes. In combination with alumina polishing, UV/ozone pretreatment produces electrodes with high activity for oxidation of catecholamines and ascorbic acid. UV/ozone treatment also reverses the passivating effect of sonicating GC electrodes in protic solvents and minimizes adsorption of dopamine and 4-methyl catechol. UV/ozone treatment also cleans electrodes fouled by electrolysis by-products. Fifteen minutes of UV/ozone treatment produced near complete restoration of activity at a GC electrode passivated by a phenolic polymer film. UV/ozone treatment increases activity by oxidative removal of organic adsorbates and a polishing-produced carbon-powder overlayer. In addition, XPS and cyclic voltammetry indicate that carbon-oxide concentration increases on the surface of the UV/ozone treated carbon electrode as compared to an alumina-polished electrode.     

Attachment of gold nanoparticles to glassy carbon electrode and its application for the voltammetric resolution of ascorbic acid and dopamine

Gold nanoparticles have been attached on glassy carbon electrode surface through sulfhydryl-terminated monolayer and the gold nanoparticles-immobilized glassy carbon electrodes have been applied to the electrocatalytic oxidation of ascorbic acid, reducing the overpotential by about 200 mV with obviously increased current response. Due to its strong electrocatalytic activity towards ascorbic acid, the gold nanoparticles modified electrode can resolve the overlapped voltammetric waves of ascorbic acid and dopamine into two well-defined voltammetric peaks with peak-to-peak separation in potentials of about 300 mV. This can be used to allow the selective determination of ascorbic acid in the presence of dopamine. The catalytic current obtained from differential pulse voltammetry is linearly dependent on ascorbic acid concentration over the range of 6.5 × 10^?6 to 1.45 × 10^?4 M with correlation coefficient of 0.998 in the presence of dopamine. The detection limit (3σ) for AA was found to be 2.8 × 10^?6 M. The simultaneous determination of ascorbic acid and dopamine in their binary mixture has also been investigated. The modified electrode shows good selectivity, stability and anti-fouling properties. The proposed methods have been used for the selective determination of ascorbic acid in the presence of dopamine and for the simultaneous determination of both them in their mixtures with satisfactory results.     

Electrochemical analysis of ascorbic acid using copper nanoparticles/polyaniline modified glassy carbon electrode

The electrosynthesis of polyaniline (PANI) film has been achieved on glassy carbon electrode (GCE) in a novel ionic liquid medium by means of cyclic voltammetry (CV). Then a copper nanoparticles (Cu-NPs) film was in situ electrochemically deposited on the surface of PANI/GCE. Electrochemical behavior and surface characteristics of the Cu-NPs/PANI/GCE were studied using cyclic voltammetry, scanning electron microscopy (SEM) and the results confirmed the presence of PANI and Cu-NPs on the electrode surface. Cu-NPs were highly dispersed and firmly stabilized by surface attachment of the PANI, which was prepared in ionic liquid and strongly attached to the electrode surface. The Cu-NPs/PANI/GCE showed excellent electrocatalytic activity toward the oxidation of ascorbic acid (AA) under weakly basic conditions. Amperometry was carried out to determine the concentration of AA at 0.2 V, and a good linear concentration range from 0.005 to 3.5 mM was found. The Cu-NPs/PANI composite film on GCE surface showed good reproducibility and stability.     

Corrigendum to: “Use of dynamically adaptive grid techniques for the solution of electrochemical kinetic equations. Part 7. Testing of the finite-difference patch-adaptive strategy on example kinetic models with moving reaction fronts,in one-dimensional space geometry” [J. Electroanal. Chem. 481 (2000) 152–167]

Choline (Ch) and acetylcholine (ACh) modified glassy carbon electrodes have been prepared and characterized by X-ray photoelectron spectroscopy (XPS), UV–visible spectroelectrochemistry (UV–Vis), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modification of ACh was that the Ch was covalently bounded on the electrode surface accompanied by acetate anions embedded and adsorbed by electrostatics in the Ch modified layer, forming a novel choline/acetate interdigitate assembly. This provided an excellent example of a mixed two-component modification from a native acetylcholine molecule on a carbon electrode. These two modified electrodes were applied to the electrocatalytic oxidation of dopamine (DA), serotonin (5-HT) and ascorbic acid (AA), and resolved the overlapping of the anodic peaks of DA, 5-HT and AA into three well-defined voltammetric peaks in CV or different pulse voltammetry (DPV). This can be used for simultaneous determination of these species in a mixture. The stability of the acetate/choline/glass carbon electrode (ACh/GCE) sensing system was good, with up to at least 30 days of continual operation.     

Electrocatalytic oxidation of dopamine at aluminum electrode modified with nickel pentacyanonitrosylferrate films,synthesized by electroless procedure

The electrocatalytic oxidation of dopamine (DA) at a home-made aluminum electrode modified with nickel pentacyanonitrosylferrate (NiPCNF) film, has been studied by electrochemical approaches. The immobilization of NiPCNF film was performed by a simple dip-coating procedure. The cyclic voltammogram of the resulting modified Al electrode prepared under optimum conditions, shows a well-behaved redox couple due to the [Ni^IIFe^III/II(CN)₅NO]^0/?1 system. The NiPCNF films, formed on the Al electrode show excellent electrocatalytic activity toward the oxidation of DA. The effect of the solution pH on the voltammetric response of DA was examined using phosphate buffer solution of different pHs. Under optimum conditions a linear calibration graph was obtained over the DA concentration range 2–33 mM. The kinetics of the catalytic reaction were investigated by cyclic voltammetry and rotating disk electrode voltammetry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The rate constant for the catalytic reaction k, the diffusion coefficient of DA in the solution D, the electron diffusion coefficient in the film D_e and transfer coefficient α, were found to be 3.1×10² M^?1 s^?1, 3.4×10^?6 cm² s^?1, 2.2×10^?11 cm² s^?1 and 0.67, respectively. The interference of ascorbic acid was investigated and greatly reduced using a thin film of Nafion^® on the surface-modified electrode. Further examination of the modified electrode shows that the modifying layers (NiPCNF) on the aluminum substrate show reproducible behavior and a high level of stability during electrochemical experiments, making it interesting for analytical applications.     

Simultaneous electrochemical detection of uric acid and ascorbic acid at a poly(N,N-dimethylaniline) film-coated GC electrode

A polymer film of N,N-dimethylaniline (PDMA) having a positive charge on the quarternary ammonium group in its backbone was electrochemically deposited on a glassy carbon (GC) electrode surface. The resulting film-coated GC electrode was used to detect uric acid (UA) electrochemically in the presence of ascorbic acid (AA). Both UA and AA are anionic in a solution of pH 7 and thus were attracted to the film, which lowered their oxidation potentials and increased their oxidation currents. In cyclic voltammetric measurements, the negative shift of the oxidation potential of UA (by 0.28 V) compared with that at the bare electrode was larger than that of AA (by 0.2 V). Also the increase in the oxidation current of UA at the PDMA film-coated electrode was larger than that of AA. In square wave voltammetric measurements, the PDMA film-coated electrode could separate the oxidation peak potentials of UA and AA present in the same solution by about 200 mV though the bare electrode gave a single broad response. A successful elimination of the fouling effect by the oxidized product of AA on the response of UA has been achieved at the PDMA film-coated electrode. The detection limit of UA in the presence of 160-fold excess of AA was found as 1.25 μM and the current response for UA increased linearly with increase of its concentration from 1.25 to 68.75 μM in the presence of AA with a correlation coefficient of 0.999 and a sensitivity of 0.0276 μA μM⁻¹. In flow injection analysis, a good linear relationship between the oxidation current and the concentration from 2 to 21 μM of UA was found. The sensitivity of the PDMA film-coated electrode towards UA was calculated as 0.0285 μA μM⁻¹ with a correlation coefficient of 0.997. The stable and reproducible response for both AA and UA at the PDMA film-coated electrode was verified by flow injection experiments. As the response of UA was reproducible in the presence of AA, it was expected that the oxidized product of AA would not affect the electrode response of UA. Moreover, the physiologically common interferents (i.e., glucose, purine, urea and citrate) negligibly affected the response of UA. The PDMA film-coated electrode exhibited a stable and sensitive response to UA in the presence of interferents.     

A differential pulse voltammetric method for simultaneous determination of ascorbic acid,dopamine, and uric acid using poly (3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid) film modified glassy carbon electrode

A stable modified glassy carbon electrode based on the poly 3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (CDDA) film was prepared by electrochemical polymerization technique to investigate its electrochemical behavior by cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and their stability were examined. The homogeneous rate constant, k_s, for the electron transfer between CDDA and glassy carbon electrode was calculated as 5.25(±0.20) × 10² cm s⁻¹. The modified electrode showed electrocatalytic activity toward ascorbic acid (AA), dopamine (DA), and uric acid (UA) oxidation in a buffer solution (pH 4.0) with a diminution of their overpotential of about 0.12, 0.35, and 0.50 V for AA, DA, and UA, respectively. An increase could also be observed in their peak currents. The modified glassy carbon electrode was applied to the electrocatalytic oxidation of DA, AA, and UA, which resolved the overlapping of the anodic peaks of DA, AA, and UA into three well-defined voltammetric peaks in differential pulse voltammetry (DPV). This modified electrode was quite effective not only for detecting DA, AA, and UA, but also for simultaneous determination of these species in a mixture. The separation of the oxidation peak potentials for ascorbic acid–dopamine and dopamine–uric acid were about 0.16 V and 0.17 V, respectively. The final DPV peaks potential of AA, DA and UA were 0.28, 0.44, and 0.61 V, respectively. The calibration curves for DA, AA, and UA were linear for a wide range of concentrations of each species including 5.0–240 μmol L⁻¹ AA, 5.0–280 μmol L⁻¹ DA, and 0.1–18.0 μmol L⁻¹ UA. Detection limits of 1.43 μmol L⁻¹ AA, 0.29 μmol L⁻¹ DA and 0.016 μmol L⁻¹ UA were observed at pH 4. Interference studies showed that the modified electrode exhibits excellent selectivity toward AA, DA, and UA.     

Selective determination of dopamine in the presence of ascorbic acid at a multi-wall carbon nanotube-poly(3,5-dihydroxy benzoic acid) film modified electrode

A sensitive and selective method for determination of dopamine (DA) using multi-wall carbon nanotube (MWCNT)-poly(3,5-dihydroxy benzoic acid) [poly(DBA)] modified electrode is developed. The modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solutions at pH 7.4. Using cyclic voltammetry, the linear range of 1 × 10⁻⁷–7.0 × 10⁻⁵ M in the interference of 500 μM ascorbic acid (AA) and the detection limit of 1.0 × 10⁻⁸ M were estimated for the measurement of DA in pH 7.4 phosphate buffer solutions. The value of DA current retained 98.36% of the initial response current after the modified electrode exposed to the air for one week. The interference studies showed that the modified electrode excludes effectively large excess of AA. The kinetic characteristics of the transfer of DA demonstrated that the electron propagation between DA and electrode was accelerated at MWCNT-poly(DBA) modified electrode. The work provided a valid and simple approach to selectively detect dopamine in the presence of AA in physiological environment.     

Electrochemical properties of a tetrabromo-p-benzoquinone modified carbon paste electrode. Application to the simultaneous determination of ascorbic acid,dopamine and uric acid

The electrochemical study of a tetrabromo-p-benzoquinone modified carbon paste electrode (TBQ-MCPE), as well as its efficiency for electrocatalytic oxidation of ascorbic acid, dopamine and uric acid, is described. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. Three linear segments were found with slope values of ?58.4 mV/pH, ?28.1 mV/pH and 0.0 mV/pH in the pH range 2.0–7.1, pH 7.1–9.0 and pH 9.0–11.0, respectively. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between TBQ and CPE were calculated as 3.79 ± 0.10 s^?1 and 0.55, respectively. The electrode was also employed to study the electrocatalytic oxidation of AA, using cyclic voltammetry, chronoamperometry and differential pulse voltammetry as diagnostic techniques. It has been found that the oxidation of AA at the surface of TBQ-MCPE occurs at a potential of about 430 mV less positive than that of an unmodified CPE. The diffusion coefficient of AA was also estimated using chronoamperometry. The kinetic parameters such as the electron transfer coefficient, α, and heterogeneous rate constant, $k_{\mathrm{h}}^{\prime }$, for oxidation of AA at the TBQ-MCPE surface was determined using cyclic voltammetry. Differential pulse voltammetry (DPV) exhibits two linear dynamic ranges and a detection limit of 0.62 μM for AA. In DPV, the TBQ-MCPE could separate the oxidation peak potentials of AA, DA and UA present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. This modified electrode was quite effective not only to detect AA, DA and UA, but also in simultaneous determination of each component concentration in the mixture.     

Metal-dispersed porous carbon films as electrocatalytic sensors

The attractive features of ultrathin porous carbon films have been coupled with the efficient catalytic action of dispersed metal particles. In particular, loading of these submicrometer foams with ruthenium or platinum centers offers a dramatic increase in the electron transfer rates of important redox systems, such as NADH, uric acid, ascorbic acid, acetaminophen, hydrazine or hydrogen peroxide. Characterization of the electrocatalytic behavior (with respect to the pH, scan rate or metal loading) and the attractive low-potential analytical (sensing) performance are reported. Scanning electron microscopy sheds useful insights into the distribution of the metals within the porous electrode matrix.     

Electrocatalytic oxidations of biological molecules (ascorbic acid and uric acids) at highly oxidized electrodes

Highly oxidized glassy carbon and other metal (gold and platinum) electrode surfaces were generated by applying 2.0 V vs. SCE for 600 s in pH 7 solution. The effects of oxidation on the functional, physical, and chemical characteristics of the electrodes went beyond the usual conditioning of such electrode surfaces through cycling to slightly beyond the medium decomposition potentials. The oxidized electrodes showed enhanced electrochemical activities and lower background currents. Besides cleaning the surface of contaminants introduced in the polishing stage of electrode preparation, application of such high potentials for an extended time interval changed the chemical nature of the glassy carbon surface itself. The chemical changes influenced the electro-oxidation reaction of bio-molecules such as ascorbic acid and uric acid but did not influence the reaction of the ferri- and ferrocyanide system. As a result the biological molecules (uric acid and ascorbic acid) were detected using an electrochemical method individually and simultaneously without the necessity for any electron relay complex.     

Uncovering the influence of antioxidants on polyphenol oxidation in wines using an electrochemical method: Cyclic voltammetry

The influence of sulfur dioxide, glutathione and ascorbic acid on the cyclic voltammograms of four representative wine polyphenols (catechin, caffeic acid, rutin and quercetin) and five different wines was investigated using a glassy carbon electrode in a model wine solution. Sulfur dioxide increased the anodic current and decreased the cathodic current for all four polyphenols and all wines, pointing to a rapid interaction of SO₂ with the oxidized polyphenol quinones. A similar trend was seen for glutathione, except that in the case of quercetin, addition of glutathione led to the formation of a second set of voltammetric peaks, corresponding to redox activity of a glutathione derivative. However, ascorbic acid produced no additional effect on the cyclic voltammograms of wine polyphenols and wines, beyond that expected for a simple sum of the polyphenol and ascorbic acid responses, with the exception that adsorption of quercetin and rutin on the carbon electrode caused a shift in the ascorbic acid oxidation peak to more positive potentials.     

Kinetics of oxygen reduction on gold nanoparticle/multi-walled carbon nanotube hybrid electrodes in acid media

In this paper, the electrochemical reduction of oxygen has been studied on gold nanoparticle/multi-walled carbon nanotube (AuNP/MWCNT) modified glassy carbon (GC) electrodes in 0.5 M H₂SO₄ using the rotating disk electrode (RDE) method. The AuNP/MWCNT catalysts were prepared by chemical deposition of AuNPs onto MWCNTs spontaneously grafted with 4-nitrophenyl groups. The composite electrode was characterised by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The oxygen reduction behaviour of these electrodes was compared with that of a bulk gold electrode. The AuNP/MWCNT catalyst showed a pronounced electrocatalytic activity towards O₂ reduction in acid media. The half-wave potential of O₂ reduction on the AuNP/MWCNT catalyst shifted ca 80 mV to more positive potentials as compared to that of a polished Au electrode. The kinetic parameters of oxygen reduction were determined and the specific activity of the hybrid electrode was slightly higher than that of the bulk Au electrode.     

Amperometric determination of hydrogen peroxide on surface of a novel PbPCNF-modified carbon-ceramic electrode in acidic medium

This work describes the electrochemical behavior of lead pentacyanonitrosylferrate (PbPCNF) film immobilized on the surface of carbon-ceramic electrode (CCE) and its electrocatalytic activity toward the reduction of hydrogen peroxide in acidic medium. The electrode was prepared by electroless derivatization of Pb-doped carbon-ceramic electrode surface to the redox active PbPCNF solid film, in the presence of sodium pentacyanonitrosylferrate, Na₂[Fe(CN)₅NO], (PCNF). The morphology and the composition of the PbPCNF-modified CCE were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and Fourier transform infrared (FTIR) techniques. Various experimental parameters influencing the electrochemical behavior of the modified electrode were optimized by varying the supporting electrolyte, potential scan rates and solution pH. The modified electrode showed an excellent electrocatalytic behavior toward the reduction of hydrogen peroxide in 0.5 M KNO₃ at pH 4. The sensor exhibited a good linear response for H₂O₂ concentration over the range 0.5–58.75 μM with a detection limit of 0.4 μM (S/N = 3). The interferences of dopamine (DA), uric acid (UA), and ascorbic acid (AA) were negligible in the determination of H₂O₂. The proposed sensor showed good stability, reproducibility and outstanding for long-term use.     

Electrocatalytic oxidation and reduction of H2O2 on vertically aligned Co3O4 nanowalls electrode: Toward H2O2 detection

Single crystal and vertically aligned cobalt oxide (Co₃O₄) nanowalls were synthesized by directly heating Co foil on a hot-plate under ambient conditions. The vertically aligned Co₃O₄ nanowalls grown on the plate show excellent mechanical property and were facilely attached to the surface of a glassy carbon (GC) electrode using conductive silver paint. The prepared Co₃O₄ nanowalls electrode was then applied to study the electrocatalytic oxidation and reduction of hydrogen peroxide (H₂O₂) in 0.01 M pH 7.4 phosphate buffer medium. Upon the addition of H₂O₂, the Co₃O₄ nanowalls electrode exhibits significant oxidation and reduction of H₂O₂ starting around +0.25 V (vs. Ag/AgCl), while no obvious redox activity is observed at a bare GC electrode over most of the potential range. The superior electrocatalytic response to H₂O₂ is mainly attributed to the large surface area, minimized diffusion resistance, high surface energy, and enhanced electron transfer of the as-synthesized Co₃O₄ nanowalls. The same Co₃O₄ nanowalls electrode was also applied for the amperometric detection of H₂O₂ and showed a fast response and high sensitivity at applied potentials of +0.8 V and −0.2 V (vs. Ag/AgCl), respectively. The results also demonstrate that Co₃O₄ nanowalls have great potential in sensor and biosensor applications.     

Selective determination of dopamine using unmodified,exfoliated graphite electrodes

Selective determination of a neurotransmitter, dopamine (DA), is achieved in the presence of ascorbic acid (AA) at neutral pH on an inert, unmodified exfoliated graphite electrode. The edge planes, exposed by roughening the surface of the electrode have been found to be very active for electrochemical sensing. A separation of 0.24 V in the oxidation potential and an increase of 100 times in the currents between DA and AA have been observed with the graphite exfoliated at 800 °C. The exfoliation temperature is found to play a major role in determining the activation of the surface and in turn the effective separation of the analytes. This is attributed to the trend in the O/C ratios on the graphite electrodes observed using X-ray photoelectron spectroscopy. The separation is mainly due to the repulsive interactions between the functional groups on the electrode surface and the ascorbate anion. This is confirmed by comparing the point of zero charge (pH_PZC) of the electrode surface determined using pH titration and the pK_a of AA. A very low detection limit of 50 nM of DA in the presence of 100 μM ascorbic acid has been observed using chronoamperometry. The exfoliated graphite is an unmodified electrode and hence just polishing the electrode could expose the active surface. The analytical utility of the exfoliated graphite electrodes for the selective determination of DA in the presence AA is presented.     

High dispersion and electrocatalytic properties of Pt nanoparticles on SWNT bundles

Platinum (Pt) nanoparticles were electrochemically dispersed on single-walled carbon nanotube (SWNT) bundles by electro-reduction of the Pt(IV) complex formed on the SWNT surface. The structure and elemental composition of the resulting Pt/SWNT composite were characterized by transmission electron micrograph (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic properties of the Pt/SWNT electrode for methanol oxidation have been investigated by cycle voltammetry (CV). A high electrocatalytic activity and excellent stability of the Pt/SWNT electrode can be observed. This may be attributed to the high dispersion of platinum nanoparticles and the particular properties of the SWNT supports. The results imply that the Pt/SWNT composite has good potential applications in fuel cells.