Voltammetric Response Of Dopamine Research Articles

Selective response of dopamine in the presence of ascorbic acid at multi-walled carbon nanotube modified gold electrode

The acid-treated multi-walled carbon nanotubes (MWNTs), which were modified on the surface of gold electrode, offers substantial improvements in voltammetric sensitivity and selectivity towards the determination of dopamine (DA). It can inhibit the voltammetric response of ascorbic acid (AA) while the redox reaction of dopamine is promoted. When a differential pulse voltammetric (DPV) technique was used, the peak separation between DAs and AAs was 244 mV. Based on this, a selective method could be constructed to detect DA in the presence of 1000 times higher concentration of AA. The effect of various experimental parameters on the voltammetric response of dopamine was investigated. Under the chosen conditions, the peak currents are correspondent linearly to the concentrations of DA in the range of 5×10 −7∼4×10 −4 mol L −1 with a limit of detection of 2×10 −7 mol L −1. The proposed method can be applied to detect DA in real samples.

Electrochemical characteristics of dopamine oxidation at palladium hexacyanoferrate film, electroless plated on aluminum electrode

A novel electrode material was obtained at an aluminum electrode (Al) by a simple electroless method including two consecutive procedures: (i) the electroless deposition of metallic palladium on the Al electrode surface from PdCl 2 + 25% ammonia solution and (ii) the chemical transformation of deposited palladium to the palladium hexacyanoferrate (PdHCF) films in a solution containing 0.5 M K 3[Fe(CN) 6]. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of dopamine (DA). The effect of solution pH on the voltammetric response of DA has been investigated. A linear calibration graph was obtained over the DA concentration range 2–51 mM. The rate constant k and transfer coefficient α for the catalytic reaction and the diffusion coefficient of DA in the solution D, were found to be 4.67 × 10 2 M −1 s −1, 0.63 and 2.5 × 10 −6 cm 2 s −1, respectively. The interference of ascorbic acid was investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level stability during electrochemical experiments, making it particularly suitable for the analytical purposes.

Simultaneous Determination of Dopamine and Ascorbic Acid at an In‐Site Functionalized Self‐Assembled Monolayer on Gold Electrode

AbstractThe in‐site functionalization of 4‐aminothiophenol (4‐ATP) self‐assembled monolayer on gold electrode at physiological pH yields a redox active monolayer of 4′‐mercapto‐N‐phenylquinone diimine (MNPD). The functionalized electrode exhibits excellent electrocatalytic responses towards dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by about 0.22 V and 0.34 V, respectively, with greatly enhanced current responses. Due to its different catalytic activities toward DA and AA, the modified electrode resolves the overlapping voltammetric responses of DA and AA into two well‐defined voltammetric peaks by differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly related to DA and AA concentration in the ranges of 5.0×10−6−1.25×10−4 M and 8.0×10−6−1.3×10−4 M with correlation coefficient of 0.999 and 0.998, respectively. The detective limits (3σ) for DA and AA were found to be 1.2×10−6 M and 2.4×10−6 M, respectively. The modified electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.

Characterization and electrochemical studies of Nafion/nano-TiO 2 film modified electrodes

A nano-TiO 2 film from stable aqueous dispersion has been modified on a glassy carbon electrode (GCE), and was characterized by scanning electron microscopy (SEM) and surface-enhanced Raman spectroscopy (SERS). This nanostructured film exhibits an ability to improve the electron-transfer rate between electrode and dopamine (DA), and electrocatalyze the redox of DA. The electrocatalytical behavior of DA was examined by cyclic voltammetry (CV). Combined with Nafion, the bilayer-modified electrode (N/T/GCE) gives a sensitive voltammetric response of DA regardless of excess ascorbic acid (AA). Electrochemical impedance spectroscopy (EIS) at a fixed potential was performed at variously treated GCEs. The mechanism of the electrode reaction of DA at N/T/GCE and the equivalent circuits of different GCEs have been proposed.

Electroanalysis of dopamine at a gold electrode modified with N-acetylcysteine self-assembled monolayer

Voltammetric behavior of dopamine (DA) on a gold electrode modified with the self-assembled monolayer (SAM) of N-acetylcysteine has been investigated, and one pair of well-defined redox peaks of dopamine is obtained at the SAM modified gold electrode. The oxidation peak current increases linearly with the concentration of dopamine in the range of 1.0×10−6to2.0×10−4moll−1. The detection limit is 8.0×10−7moll−1. This method will be applicable to the determination of dopamine in injection of dopamine hydrochloride, and the good recovery of dopamine is obtained. Furthermore, The SAM modified gold electrode can resolve well the voltammetric responses of dopamine and ascorbic acid (AA), so it can also be applied to the determination of dopamine in the presence of ascorbic acid.

Simultaneous determination of dopamine and serotonin on a glassy carbon electrode coated with a film of carbon nanotubes

A chemically modified electrode based on the carbon nanotube film–coated glassy carbon electrode (GCE) is described for the simultaneous determination of dopamine (DA) and serotonin (5-HT). The multiwall carbon nanotube (MWNT) film–coated GCE exhibits a marked enhancement effect on the current response of DA and 5-HT and lowers oxidation overpotentials. The responses of DA and 5-HT merge into a large peak at a bare GCE, but they yield two well-defined oxidation peaks at the MWNT film–coated GCE. The experimental parameters were optimized, and a direct electrochemical method for the simultaneous determination of DA and 5-HT was proposed. The interference of ascorbic acid (AA) was investigated, and the results showed that a large excess of AA did not interfere with the voltammetric responses of DA and 5-HT. The modified electrode has been successfully applied for the assay of 5-HT and DA in human blood serum.

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 3.1×10 2 M −1 s −1, 3.4×10 −6 cm 2 s −1, 2.2×10 −11 cm 2 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.

Covalent modification of glassy carbon electrodes with beta-alanine for voltammetric separation of dopamine and ascorbic acid.

beta-Alanine was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation process of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) proved the immobilization of beta-alanine monolayer on GCE. The electrode shows strong electrocatalytic functions to dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by 0.20 V and 0.23 V, respectively. Due to its different catalytic effects toward DA and AA, the modified electrode resolved the overlapping voltammetric responses of DA and AA into two well-defined voltammetric peaks by CV or differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly related to DA and AA concentrations in the ranges of 4.0 x 10(-6)-5.0 x 10(-4) mol/L and 2.0 x 10(-5)-6.0 x 10(-3) mol/L with correlation coefficients of 0.997 and 0.995, respectively. The detection limits (3 sigma) for DA and AA were 2.4 x 10(-6) mol/L and 1.2 x 10(-5) mol/L, respectively. The electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.

Covalent modification of glassy carbon electrodes with glycine for voltammetric separation of dopamine and ascorbic acid.

Glycine was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry proved the immobilization of glycine on the GCE. The modified electrode reduced the overpotentials of dopamine (DA) and ascorbic acid (AA) by approximately 0.15 V and 0.23 V, respectively, and resolved the overlapping voltammetric response of DA and AA into two well-defined voltammetric peaks in cyclic voltammetry (CV) or differential pulse voltammetry (DPV), unlike the unmodified GCE; this can be used for the simultaneous determination of these species in a mixture. The differential pulse peak current was linearly dependent on DA and AA concentration in the range 5 x 10(-6)-8 x 10(-4) mol L(-1) and 6 x 10(-5)-4 x 10(-3) mol L(-1), with correlation coefficients of 0.996 and 0.994, respectively. The detection limits (3delta) for DA and AA were 1.8 x 10(-6) mol L(-1) and 2.1 x 10(-5) mol L(-1), respectively. The modified electrode is very sensitive, selective and stable, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.

Voltammetric Determination of Dopamine in a Mixture of Dopamine and Ascorbic Acid at a Deactivated Polythiophene Film Modified Electrode

The voltammetric responses of dopamine (DA) and ascorbic acid (AA) at a deactivated polythiophene (PT) film modified electrode were investigated. It was found that DA displays nearly identical voltammetric response at both a bare and the modified electrode, while the voltammetric signal of AA is greatly suppressed at the modified electrode due to the repulsion between it and the deactivated film. Various experimental parameters affecting the voltammetric responses of DA and AA were studied. The modified electrode was demonstrated to be very useful in selectively determining DA in a mixture of DA and AA. At a 0.5 μm deactivated PT film modified electrode the calibration curve of DA was linear over the range of 0.8 μM - 1.0 mM in the presence of 1.0 mM AA. The detection limit was 0.4 μM.

Voltammetric Behaviors of Dopamine and Ascorbic Acid at a Glassy Carbon Electrode Anodized in 1,ω-Alkanediol

The voltammetric behaviors of dopamine (DA) and ascorbic acid (AA) at a glassy carbon (GC) electrode anodized in 1,ω-alkanediol were examined. On cyclic voltammetry (CV) at a 1,5-pentanediol-modified GC electrode, the electrode process of AA was totally depressed, while DA still showed an anodic peak. Although similar phenomena were observed at a GC electrode anodized in 1,3-propanediol or 1,4-butanediol, the 1,5-pentanediol-modified electrode suppressed the anodic peak of AA most strongly. The voltammetric response of DA at the modified electrode was enhanced by the presence of AA, and the extent was controllable by a proper selection of the sweep rate. Thus, the electrochemical detection of DA with high sensitivity was achieved through CV with 0.1 V s−1 at the modified electrode by adding excess AA, while electrochemical discrimination of DA from excess AA was realized at 20 V s−1.

Permeability controllable overoxidised polypyrrole film modified glassy carbon electrodes

A voltammetric study on overoxidised polypyrrole (PPy) film modified electrodes is reported. These electrodes show permselective and accumulative properties towards cationic dopamine (DA). The exclusion of anionic ascorbate offers substantial improvement in the selectivity of DA determination. Differences in voltammetric responses of DA and ascorbate are attributed to the charge and porosity of the film. The volume of doping ions used for PPy preparation takes an important role in the film permeability. Other factors such as film thickness and preconcentration time are also investigated.

Voltammetric determination of dopamine in the presence of ascorbic acid at over-oxidized polypyrrole-indigo carmine film-coated electrodes.

Over-oxidized polypyrrole films doped with indigo carmine (PPy-IC) offer substantial improvements in voltammetric sensitivity and selectivity towards dopamine. This polymer coating attenuates the voltammetric response of ascorbic acid while the oxidation peak current of dopamine is enhanced by over one order of magnitude compared with that at the bare electrode. The high sensitivity and selectivity for dopamine appears to be mainly due to the charge discrimination and the analyte accumulation. The detection limit is dependent on both film thickness and preconcentration time. At a 0.25 micron thick PPy-IC film-coated electrode, for a 2 min preconcentration time, the detection limit is 10(-8) mol l-1, over two orders of magnitude lower than at a bare glassy carbon electrode. The concomitant ascorbic acid shows no interference although its concentration is as high as 0.1 mmol l-1. The effects of various experimental parameters on the voltammetric response of dopamine were also investigated. The attractive permselective and preconcentrating properties of the PPy-IC films make them valuable for in vivo electrochemistry.

Voltammetric response of dopamine at an overoxidised polypyrrole–dodecyl sulfate film coated electrode

Overoxidised polypyrrole–dodecyl sulfate film coated glassy carbon electrode shows improved voltammetric sensitivity and selectivity toward dopamine.