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.     

Poly(N-methylaniline)/nickel modified carbon paste electrode as an efficient and cheep electrode for electrocatalytic oxidation of formaldehyde in alkaline medium

This research in finding a cheap and efficient catalyst for electrooxidation of formaldehyde give us an attempt to make and examine the behavior of poly(N-methylaniline)/nickel modified carbon paste electrode (Ni/P(NMA)/MCPE) in absence and presence of formaldehyde. This involves in situ electropolymerization of N-methylaniline at carbon paste electrode, which is following to the incorporation of Ni(II) to polymeric layer by immersion of modified electrode in 1.0 M nickel sulphate solution. The electrocatalytic oxidation of formaldehyde was studied by cyclic voltammetry and chronoamperometry methods. The effects of scan rate and formaldehyde concentration on the electrocatalytic oxidation of formaldehyde were also investigated at the surface of Ni/P(NMA)/MCPE. The diffusion coefficient (D = 14.1 × 10⁻⁵ cm² s⁻¹), and some kinetic parameters such as the transfer coefficient (α = 0.45) and also second-order rate constant (k = 8.96 × 10⁻⁴ cm³ mol⁻¹ s⁻¹) of formaldehyde were calculated.     

Electrocatalytic oxidation of some amino acids on a cobalt hydroxide nanoparticles modified glassy carbon electrode

In this study we investigated the electrocatalytic oxidation of cysteine, cystine, N-acetyl cysteine, and methionine on cobalt hydroxide nanoparticles modified glassy carbon electrode in alkaline solution. Different electrochemical techniques such as cyclic voltammetry, chronoamperometry and steady-state polarization were used to track the oxidation process and its kinetics. From voltammetric studies we concluded that in the presence of amino acids the anodic peak current of Co(IV) species increased, followed by a decrease in the corresponding cathodic current peak. This indicates that amino acids were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron’s equation, the values of α_s and k_s for the immobilized redox species were determined as α_s,a = 0.63, α_s,c = 0.38 and k_s = 0.28 s⁻¹, respectively. The catalytic rate constants, the electron transfer coefficients and the diffusion coefficients involved in the electrocatalytic oxidation of amino acids were determined.     

Electrochemistry of magnolol and interaction with DNA

The electrochemical behaviors of magnolol have been studied at glassy carbon electrode using cyclic voltammetry, linear sweep voltammetry and chronocoulometry. Moreover, its interaction with DNA was investigated in solution by electrochemical methods and ultraviolet–visible spectroscopy. The experiment results indicated that the electrochemical oxidation of magnolol was an irreversible process with one proton and one electron transfer. The electron transfer coefficient (α) was calculated to be 0.441 ± 0.001. At the scan rate from 100 mV/s to 450 mV/s, the electrode process was controlled by the adsorption step and at the range of 600–950 mV/s the electrochemical oxidation was diffusion controlled process. The corresponding electrochemical rate constant (k_s) was 0.0760 ± 0.0001 s⁻¹. Through chronocoulometry experiment, the diffusion coefficient (D) and the surface concentration (Γ) were obtained as (3.76 ± 0.01) × 10⁻⁷ cm²/s and (2.98 ± 0.01) × 10⁻¹⁰ mol/cm². In addition, the interaction of magnolol and DNA was ascribed to be electrostatic interaction and the calculated association constant (β) and Hill coefficient (m) were 1.14 × 10⁵ M⁻¹ and 0.973. At last a sensitive and convenient electrochemical method was proposed for the determination of magnolol.     

Electrocatalytic oxidation of hydrazine using glassy carbon electrode modified with carbon nanotube and terpyridine manganese(II) complex

Here, we report a simple and extremely effective method to modify a glassy carbon (GC) electrode with carbon nanotubes (CNTs) and [Mn(CH₃COO)(CH₃OH)₂(pyterpy)]ClO₄, (pyterpy = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine) complex. The kinetics of the reaction between, the terpyridine manganese(II) complex, mediator and hydrazine has been characterized using cyclic voltammetry and rotating disk electrode voltammetry. The catalytic currents were proportional to the concentration of hydrazine giving rise to calibration curves characterized by two linear segments. The linear segment over the concentration range of 1.00 × 10⁻³–1.05 mM could be used with analytical purposes to determination of hydrazine with a detection limit of 0.50 μM and a sensitivity of 0.038 μA/μM. The heterogeneous rate constant, k′ for the oxidation of hydrazine at the surface of the modified electrode was determined by rotating disk electrode voltammetry using the Koutecky–Levich plot. The transfer coefficient (α) for electrocatalytic oxidation of hydrazine and the diffusion coefficient of this substance under the experimental conditions were also investigated. The resulting modified electrode retains its initial response for at least one month if stored dry in air.     

The role of bromine adlayer at palladium electrode in the electrochemical oxidation of dopamine in alkaline solution

A palladium electrode modified with bromine monolayer was fabricated throughout a spontaneous oxidative chemisorption of bromide ions contained in an alkaline solution. The surface coverage and the apparent double layer capacitance induced by the adsorption of bromide ions under the present applied potential indicates the formation of incomplete monolayer due to a prominent co-adsorption of hydroxyl ions (OH⁻). The film modified electrode exhibited a substantial reactivity and high sensitivity in the electrochemical oxidation of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). This trend was attributed to the structure and the composition of the bromine adlayer which renders a partial negative charge capable of attracting selectively the cationic DA and repelling anionic AA and UA. The peak currents of DA in the binary and ternary mixtures were well-separated, well-defined and increased linearly with respect to its concentration. The interference property expected by the presence of both AA and UA has been advantageously eliminated at the bromine-adlayer modified electrode. The apparent diffusion coefficient value of DA was 1.37 × 10⁻⁸ m² s⁻¹, based on an amperometric current–time study. The present system provides a simple and fundamental approach for the simultaneous and selective determination of DA in the presence of AA and UA.     

Simultaneous determination of dopamine,ascorbic acid and uric acid on ordered mesoporous carbon/Nafion composite film

Here we report the selective, sensitive and simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) on ordered mesoporous carbon (OMC)/Nafion composite film. Insoluble OMC was dispersed into ethanol in the presence of 0.5% Nafion, resulting in a stable and well-distributed OMC/Nafion suspension. After evaporation of ethanol, a uniform OMC/Nafion composite film-coated glassy carbon electrode (GCE) was achieved by simple casting deposition. The OMC/Nafion electrode shows ideal reversibility in 5 mM K₃[Fe(CN)₆] in the range of 0.02–0.50 V s⁻¹, indicating a fast electron-transfer kinetics. Moreover, due to the strong catalytic function of OMC, the overlapping voltammetric response of DA, AA and UA is well-resolved from each other with lowered oxidation potential and enhanced oxidation currents. The mechanism for the oxidation of AA, DA and UA at the OMC/Nafion film was also studied. By using differential pulse voltammetry (DPV), detection limits of 0.5, 20 and 4.0 μM were obtained for DA, AA and UA, respectively. The practical application of the electrode is successfully demonstrated for the determination of DA, AA and UA simultaneously in standard and real samples, without any preliminary treatment.     

Preparation of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode: Application to electrocatalytic oxidation of l-cysteine

Functionalized poly N,N-dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution. The electrocatalytic ability of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of l-cysteine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. In the optimum pH (6.00), the electrocatalytic ability about 480 mV and the catalytic reaction rate constant, (k_h), can be seen 3.08 × 10³ M⁻¹ s⁻¹. The catalytic oxidation peak current determined by cyclic voltammetry method was linearly dependent on the l-cysteine concentration and the linearity range obtained was 8.00 × 10⁻⁵ –2.25 × 10⁻³ M. Detection limit of this method was determined as 6.17 × 10⁻⁵ M (2σ). At a fixed potential under hydrodynamic conditions (stirred solution), the calibration plot was linear over the l-cysteine concentration range 7.40 × 10⁻⁶ M–1.38 × 10⁻⁴ M. The detection limit of the method was 6.38 × 10⁻⁶ M (2σ).     

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.     

Electrocatalytic activity of thianthrene toward one-electron oxidation of guanosine and DNA in a non-aqueous medium

In this study, the electrochemical behavior of thianthrene (TH) and its application toward the electrocatalytic oxidation of guanosine (Gs) and DNA in a non-aqueous solution are investigated using different voltammetric techniques. Guanosine and DNA are adsorbed on the glassy carbon electrode (GCE) by applying a positive potential to the GCE. The rate constant of catalytic reaction between DNA and TH and also between Gs and TH were evaluated using chronoamperometry which gave rate constants of 2.41 × 10⁶ cm³ mol⁻¹ s⁻¹ and 2.68 (±0.19) × 10⁶ cm³ mol⁻¹ s⁻¹, respectively. Also the diffusion coefficient of TH was obtained using hydrodynamic voltammetry (3.17 × 10⁻⁵ cm² s⁻¹). Furthermore, using hydrodynamic voltammetry, a one-electron mechanism for oxidation of Gs is suggested.     

Silver nanoparticles modified carbon nanotube paste electrode for simultaneous determination of dopamine and ascorbic acid

A novel modified carbon-paste electrode was employed for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) with good selectivity and high sensitivity. Silver nanoparticle and carbon nanotube modified carbon-paste electrode (Ag/CNT–CPE) displayed excellent electrochemical catalytic activities towards dopamine (DA) and ascorbic acid (AA). The oxidation overpotentials of DA and AA were decreased significantly compared with those obtained at the bare CPE. Differential pulse voltammetry was used for the simultaneous determination of DA and AA. The peak separation between DA and AA was 67 mV. The calibration curves for DA and AA were obtained in the range of 8.0 × 10⁻⁷–6.4 × 10⁻⁵ M and 3.0 × 10⁻⁵–2.0 × 10⁻³ M, respectively. The lowest detection limits (S/N = 3) were 3.0 × 10⁻⁷ M and 1.2 × 10⁻⁵ M for DA and AA, respectively. Method was applied to the determination of DA and AA in real samples.     

Application of ionic liquid–dsDNA biocomposite film for the direct electrochemistry of myglobin on carbon ionic liquid electrode

An ionic liquid (IL) and double-stranded DNA (dsDNA) composite material was used to investigate the direct electron transfer of myglobin (Mb) on carbon ionic liquid electrode (CILE). The presence of the IL–dsDNA biocomposite film on the electrode surface provided great improvement to the direct electron transfer rate of Mb with the CILE, which was due to the synergistic contributions of specific characteristics of dsDNA, IL and their interaction. The electrochemical parameters of Mb in the IL–dsDNA composite film modified electrode were carefully investigated with the charge transfer coefficient (α) and the electron transfer rate constant (k_s) calculated as 0.42 and 0.84 s⁻¹, respectively. The fabricated Mb modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid and H₂O₂, which showed the potential applications in the third-generation electrochemical biosensor.     

Electrodeposited indigotetrasulfonate film onto glutaraldehyde-cross-linked poly-l-lysine modified glassy carbon electrode for detection of dissolved oxygen

The nano composited film of indigotetrasulfonate (ITS) electrodeposited onto poly-l-lysine (PLL)–glutaraldehyde (GA) (ITS/PLL–GA) was modified on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. Composited of the proposed film was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and UV–vis spectrum for the absorption at λ_max at 566 nm. For the electrocatalytic reduction of dissolved oxygen, ITS/PLL–GA film modified electrodes was determined in 0.1 M acetate buffer solution (pH 5.6) by cyclic voltammetry and rotating disk electrode voltammetry. This dissolved oxygen electrochemical sensor exhibited a linear response range (from 0 to 178.4 μM, R² = 0.9949), lowest detection limit (2.2 μM), lowest overpotential at −0.09 V, high sensitivity (906 μA mM⁻¹) and relative standard deviation (RSD) for determining dissolved oxygen (n = 3) was 4.2%. In addition, the ITS/PLL–GA/GCE was advantageous in terms of its simple preparation, specificity, stability and the ability of regeneration.     

Simultaneous determination of adenine and guanine utilizing PbO2-carbon nanotubes-ionic liquid composite film modified glassy carbon electrode

A novel and reliable electrochemical sensor based on PbO₂-carbon nanotubes-room temperature ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) composite film modified glassy carbon electrode (GCE) (PbO₂–MWNT–RTIL/GCE) was proposed for simultaneous and individual determination of guanine and adenine. The guanine and adenine oxidation responses were monitored by differential pulse voltammetric (DPV) measurement. Compared with the bare electrode, the PbO₂–MWNT–RTIL/GCE not only significantly enhanced the oxidation peak currents of guanine and adenine, but also lowered their oxidation overpotentials, suggesting that the synergistic effect of PbO₂, MWNT and RTIL could dramatically improve the determining sensitivity of guanine and adenine. The PbO₂–MWNT–RTIL/GCE showed good stability, high accumulation efficiency and enhanced electrocatalytic ability for the detection of guanine and adenine. Besides, the modified electrode also exhibited good behaviors in the simultaneous detection of adenine and guanine with the peak separation of 0.29 V in 0.1 M pH 7.0 phosphate buffer solution (PBS). Under the optimal conditions, the detection limit for individual determination of guanine and adenine was 6.0 × 10⁻⁹ M and 3.0 × 10⁻⁸ M (S/N = 3), respectively. The proposed method for the measurements of guanine and adenine in herring sperm DNA was successfully applied with satisfactory results.     

Electrochemical layer-by-layer modified imprinted sensor based on multi-walled carbon nanotubes and sol–gel materials for sensitive determination of thymidine

A novel electrochemical sol–gel imprinted sensor for sensitive and convenient determination of thymidine was developed. Thin film of molecularly imprinted sol–gel polymers with specific binding sites for thymidine was cast on carbon electrode by electrochemical deposition. Multi-walled carbon nanotubes (MWCNTs) were introduced for the enhancement of electronic transmission and sensitivity. The morphology and performance of the imprinted film was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and amperometric measurements (i–t) in detail. The results showed that the imprinted film exhibited high selectivity toward thymidine. The linear range is over the range from 2 to 22 μmol L⁻¹, and the linear regression equation for thymidine is I = 0.867C + 0.232 with the detection limit of 1.6 × 10⁻⁹ mol L⁻¹(S/N = 3). The imprinted sensor was successfully employed to detect thymidine in some zidovudine-tablet samples.     

Short-time preparation and electrochemical properties of a single layer of tetraoctylammonium bromide capped Au nanoparticles on dithiol self-assembled monolayer-modified Au electrode

Short time immobilization of densely packed tetraoctylammonium bromide (TOAB) stabilized gold nanoparticles (AuNPs) were established on a Au electrode modified with a self-assembled monolayer (SAM) of 1,6-hexanedithiol (HDT) or 1,4-benzenedimethanethiol (BDMT). The quartz crystal microbalance experiment showed densely packed TOAB–AuNPs single layer formation on both SAMs was achieved within 20 min. AFM images demonstrated that the immobilized TOAB–AuNPs on the SAMs were densely packed and the AuNPs film thickness was 6–7 nm. The electronic communication between the immobilized AuNPs and the underlying bulk electrode was confirmed by cyclic voltammetry and electroreflectance spectroscopy. A reversible electron transfer reaction was observed for both [Fe(CN)₆]^4−/3− and [Ru(NH₃)₆]^2+/3+ at TOAB–AuNPs immobilized on HDT (Au/HDT/AuNPs) and BDMT (Au/BDMT/AuNPs) modified electrodes. The electroreflectance spectra show a red-shifted strong positive-going plasmon resonance bands at 551 nm and 584 nm, respectively, for the Au/BDMT/AuNPs and Au/HDT/AuNPs electrodes. The observed reversible redox response for the solution redox species and red-shifted plasmon resonance bands for the immobilized AuNPs again indicated that the AuNPs were immobilized on the SAMs in a densely packed manner. An advantage of TOAB–AuNPs modified electrode prepared by short time immersion over citrate-stabilized AuNPs modified electrode was demonstrated by the enhanced oxidation of ascorbic acid (AA) at these electrodes. The oxidation of AA was shifted to 90 mV less positive potential with higher oxidation current at TOAB–AuNPs modified electrode when compared to citrate-stabilized AuNPs modified electrode.     

Ultrasensitive determination of tungsten(VI) on pikomolar level in voltammetric catalytic adsorptive catechol-chlorate(V) system

The renewable mercury film electrode, applied for the determination of tungsten(VI) ultra traces using differential pulse catalytic adsorptive cathodic stripping voltammetry (DPCAdSV) with presence of catechol as a ligand and chlorate(V) is presented. The calibration graph obtained for W(VI) is linear from 0.025 nM (4.5 ng L⁻¹) to 130 nM (23.9 μg L⁻¹) for a preconcentration time of 30 s, with correlation coefficient of 0.9989. For the renewable mercury electrode (Hg(Ag)FE) with a surface area of 4.4 mm² the detection limit for a preconcentration time of 60 s is as low as 0.2 ng L⁻¹. The repeatability of the method at a concentration level of the analyte as low as 0.09 μg L⁻¹, expressed as RSD is 3.1% (n = 5). The proposed method was successfully applied and validated by studying the certified reference material CTA-VTL-2 and simultaneously recovery of W(VI) from spiked water samples.     

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at a chlorogenic acid modified glassy carbon electrode

The redox response of chlorogenic acid solution at an inactivated glassy carbon electrode was investigated and an ECE mechanism was proposed for the electrode process. It has been shown that the oxidation of chlorogenic acid at an activated glassy carbon electrode leads to the formation of a deposited layer of about 4.5×10^?10 mol cm^?2 at the surface of the electrode. Cyclic voltammetry was used for the deposition process and the resulting modified electrode retains the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were also examined. The pH dependence of the redox activity of these films was found to be 57 mV per pH unit, which is very close to the anticipated Nernstian dependence of 59 mV per pH unit. The modified electrode exhibits potent and persistent electrocatalysis for NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 430 mV and an increase in peak current. The electrocatalytic current increases linearly with NADH concentration from 0.1 to 1.0 mM. The apparent electron transfer rate constant, k_s, and the heterogeneous rate constant for electrooxidation of NADH, k_h, were also determined using cyclic voltammetry and rotating disk electrode voltammetry, respectively.     

Fabrication of functionalized carbon nanotube modified glassy carbon electrode and its application for selective oxidation and voltammetric determination of cysteamine

The functionalized carbon nanotube electrode was fabricated by electrodeposition of 1,2-naphthoquinone-4-sulfonic acid sodium (Nq) on single-wall carbon nanotube (SWNT) modified glassy carbon electrode (GCE). This electrode was characterized by scanning electron microscopy (SEM) and the results showed that Nq can rapidly and effectively be deposited on the surface of SWNT film with high stability. The electrochemical properties of functionalized SWNT/GCE with Nq (SWNT–Nq/GCE) were studied using cyclic voltammetry, double step potential chronoamperometry and differential pulse voltammetry methods. The results indicated that SWNT could improve the electrochemical behavior of Nq and greatly enhances its redox peak currents. The SWNT–Nq/GCE exhibited a pair of well-defined redox peaks. The experimental results also demonstrated that the Nq deposited species on SWNT could catalyze cysteamine oxidation and SWNT–Nq exhibited a high performance with lowering the overpotential by more than 710 mV. The effect of pH value, number of scans and Nq concentration were investigated on the electrochemical behavior of cysteamine. The selectivity of the reaction has been assessed with no interference from tyrosine, lysine, methionine, tryptophan, alanine and glutathione. The presented method has highly selectivity for voltammetric detection of cysteamine in the dynamic range from 5.0 × 10⁻⁶ M to 2.7 × 10⁻⁴ M and with a detection of limit (3σ) 3.0 × 10⁻⁶ M.