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.     

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.     

Electrocatalytic oxidation of sodium levothyroxine with phenyl hydrazine as a mediator at carbon paste electrode: A cyclic voltammetric study

The electrochemical oxidation of sodium levothyroxine (T₄) has been studied on carbon paste electrode (CPE) with phenyl hydrazine homogenous as mediator, using cyclic voltammetric technique in presence of 0.1 M HCl as supporting electrolyte. The charge transfer coefficient (αn_α) for T₄ in the presence and absence of phenyl hydrazine was determined. The oxidation peak currents represented a linear dependence on T₄ concentration from 0.025 mM to 0.1 mM with correlation coefficient 0.997. The effect of concentration and scan rate of sodium levothyroxine in presence of trace phenyl hydrazine concentration was studied. The scan rate effect showed the electrode process is adsorption controlled. The practical application of the phenyl hydrazine mediated CPE in the determination of T₄ in a commercial tablet sample demonstrated that it has good selectivity and high sensitivity.     

Electrochemical behavior of iodide at a nickel pentacyanonitrosylferrate film modified aluminum electrode prepared by an electroless procedure

The surface of an aluminum disk electrode was modified by a thin film of nickel pentacyanonitrosylferrate and used for electrocatalytic oxidation of iodide. The cyclic voltammogram of the modified Al electrode showed surface redox behavior due to the [Ni^IIFe^III/II(CN)₅NO]^0/1? redox couple. The modifying layer shows excellent catalytic activity toward the oxidation of iodide. Different supporting electrolytes containing different alkali metal cations affected the apparent formal potential of the redox films and thus, changed the thermodynamic tendency and kinetics of the modifying film toward the catalytic oxidation of iodide. This was explained by including the concept of a surface coverage normalized-catalytic current. The kinetics of the catalytic reaction were investigated by cyclic voltammetry and rotating disk electrode voltammetry in a suitable supporting electrolyte. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The heterogeneous rate constant for the catalytic reaction, k, diffusion coefficient of iodide in solution, D, and transfer coefficient, α, were found to be 5.8 × 10² M^?1 s^?1, 1.3 × 10^?5 cm² s^?1 and 0.66, respectively. In addition the effect of electrode surface coverage on the dynamic range of a calibration curve was investigated. Under optimum conditions a linear calibration graph was obtained over an iodide concentration range of 2–100 mM.     

A biocompatible nano TiO2/nafion composite modified glassy carbon electrode for the detection of fenitrothion

A biocompatible nano TiO₂/nafion composite modified glassy carbon electrode was developed for the detection of fenitrothion. This composite electrode was characterized by SEM, XRD, UV–visible, FTIR, TGA and cyclic voltammetry. Electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry and amperometry were used for the detection of fenitrothion. Such modified electrode produced high sensing current which is one of the promising characteristics of the electroanalytical sensor. The linear relationship between sensing current and concentration is obtained in differential pulse voltammetry technique for the fenitrothion concentration ranging from 0.2 to 4 μM with LOD and LOQ of 0.0866 and 0.2889 μM respectively. The peak currents were reproducible with the relative standard deviation of 5.1% (n = 6). The peak current obtained from the cyclic voltammetry is stable even after 50 cycles. The recovery rate for the spiked water sample was calculated and compared with the data obtained by HPLC analysis.     

Covalent modification of a glassy carbon surface by electrochemical oxidation of r-aminobenzene sulfonic acid in aqueous solution

R-aminobenzene sulfonic acid (r-ABSA) was covalently modified on a glassy carbon electrode (GCE) by electrochemical oxidation in 0.1 M KCl aqueous solution. The presence of an r-ABSA monolayer on the GCE was proven by X-ray photoelectron spectroscopy (XPS). Electron transfer to Fe(CN)₆^3? was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) on the modified electrodes in solutions of various pHs. Changes in the solution pH value result in the variation of the terminal group (sulfonic acid group) charge state, based on which its surface pK_a values are estimated. The r-ABSA monolayer film on GCE has good stability and can be used as a charge-rich precursor to assemble oppositely charged species by layer-by-layer electrostatic interaction. For example, multilayer films of anionic Fe(III) tetrakis(p-sulfonatophenyl) porphyrin (FeTSPP) and cationic polymer diazo-resins (DAR) can be obtained on the r-ABSA/GCE based on electrostatic and covalently attached interaction and the resulting modified electrodes have good electrochemical response and stability.     

Iron(III) octaethylporphyrin chloride supported on glassy carbon as an electrocatalyst for oxygen reduction

Oxygen reduction was investigated at iron(III) octaethylporphyrin chloride adsorbed on a glassy carbon electrode. The title porphyrin was adsorbed irreversibly and strongly on the surface of a glassy carbon electrode. The electrochemical behavior and stability of the modified electrode were investigated using cyclic voltammetry, chronoamperometry and rotating disk electrode methods. The modified electrode showed clear but modest electrocatalytic activity for the reduction of oxygen to a mixture of water and hydrogen peroxide in buffered solutions on both the acid and basic sides of neutral with the domination of an overpotential of about 690 mV and an increase in peak current. The heterogeneous rate constant for the reduction of O₂ at the surface of the modified electrode and the diffusion coefficient of oxygen were determined by rotation disk electrode voltammetry using the Koutecký–Levich plots. In addition, iron(III) octaethylporphyrin chloride exhibited strong catalytic activity toward the reduction of H₂O₂.     

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.     

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.     

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.     

Complex electrochemistry of flavodoxin at carbon-based electrodes: results from a combination of direct electron transfer,flavin-mediated electron transfer and comproportionation

Staircase cyclic voltammetry (SCV) and differential pulse voltammetry on fully oxidized flavodoxin from Desulfovibrio vulgaris Hildenborough at the bare glassy carbon electrode give one redox couple at a potential of ?218 mV (standard hydrogen electrode (SHE)) at pH = 7.0 with an SCV peak current proportional to the scan rate. This response is caused by flavin mononucleotide (FMN), dissociated from the protein and adsorbed onto the electrode. The midpoint potential and the pK of 6.5 are equal to the values measured with free FMN in solution. When the cationic promoter neomycin is added, one additional and diffusion controlled response is observed. The midpoint potential is ?413 mV (SHE) at pH 7.0 with a redox-linked pK of 4.8 for the reduced form. The temperature dependence is ?1.86 mV K^?1, yielding ΔS° = ?179 J mol^?1 K^?1 and ΔH° = ?12.4 kJ mol^?1. Although the starting material was 100% quinone, no response was observed around the midpoint potential of the quinone to semiquinone reduction of ?113 mV (SHE) at pH 7.0, determined in an EPR-monitored titration with dithionite. Digital simulation shows that the peak currents of the second reduction couple approach a maximum value after a few cycles if comproportionation of fully reduced and fully oxidized flavodoxin occurs in solution and a small amount of semiquinone is either present initially or is generated by mediation of electrode-bound FMN. In the latter case the heterogeneous electron transfer rate between adsorbed FMN and flavodoxin is 6.3 × 10^?6 m s^?1. The implications of this anomalous behaviour for electrochemistry on flavin enzymes like glucose oxidase are discussed.     

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.     

Electrochemical detection of ethidium bromide by using pure single-walled carbon nanotube sheet as the electrode

Sheets consisted of entire single-walled carbon nanotubes (SWNTs) were used as the working electrode for electrochemical measurement of ethidium bromide by covering a glassy carbon electrode (GCE) using the SWNT-sheet. This SWNT-sheet based electrode exhibited a fast electron transfer process on the electrode surface via the cyclic voltammetry with K₄Fe(CN)₆ as electrochemical probes. This SWNT-sheet based electrode showed also a high sensitivity toward ethidium bromide, a typically harmful, aromatic backboned chemical. The SWNT-sheet based electrode was capable of accumulating ethidium bromide to a higher concentration and therefore was capable of detecting ethidium bromide with a detection limit of 1.0 × 10⁻⁸ M.     

Electrochemical study of a metallothionein modified gold disk electrode and its action on Hg2+ cations

A novel protein monolayer modified electrode has been prepared by the self-assembly of metallothionein (MT) at a gold disk electrode. The properties of MT in Tris–HCl buffer and in the monolayer are studied by using cyclic voltammetry and differential pulse voltammetry with a gold disk electrode. In the negative sweep, the voltammogram of MT in buffer shows two small peaks and different electrochemical behaviour from that at a mercury electrode. Cd²⁺ complexed to the thionein can easily be replaced by Hg²⁺ ions, and Hg²⁺ ions can firmly adsorb in the MT monolayer with a saturation coverage of (2.78±0.29)×10^?10 mol cm^?2. This behaviour has been used to preconcentrate trace Hg²⁺ for its determination by cathodic stripping differential pulse voltammetry. The cathodic stripping peak current is proportional to Hg²⁺ concentration in the range of 0.15–3 μM and the detection limit is ca. 0.08 μM (16 ppb) with a 2 min open circuit accumulation step. The relative standard deviation is 7.2% at 0.4 μM Hg²⁺ concentration (n=4). At higher concentration the adsorption of Hg²⁺exhibits a response similar to that expected for a Langmuir adsorption isotherm with the stability constant of (4.0±0.2)×10⁵ M^?1.     

Electropolymerization of ferrocene bis-amide derivatives: a possible route to an electrochemical sensory device

The electrochemical behaviour of ferrocene bis-amide derivatives in the presence and in the absence of an alkali metal cation is described. Voltammetric studies confirm the selective complexation ability of these compounds towards Li⁺ among the alkali metal cations. Platinum and glassy carbon electrodes have been modified by electropolymerization of pyrrole-substituted ferrocene bis-amide derivatives. The influence of the alkali metal cation on both the electropolymerization step and on the redox behaviour of the resulting films has been studied. The formation of a complex between polymerizable ferrocene bis-amide derivatives and Li⁺ leads to an increase in the deposition efficiency. In aqueous media, the redox potential of the electroactive film depends on the nature and the concentration of the counter-anion of the electrolyte.     

Voltammetric determination of the iodide ion with a quinine copper(II) complex modified carbon paste electrode

A Cu(Qui)(NO₃)₂ modified-carbon paste electrode (where Qui is quinine) was constructed by incorporating Cu(Qui)(NO₃)₂ into a carbon-paste composed of graphite powder and Nujol. The modification with Cu(Qui)(NO₃)₂ resulted in a deposit of iodide ions on the electrode surface through a ligand exchange reaction. This exchange reaction was completed within 20 ms in a CHCl₃+CH₃OH solution. The rate constant, k⁰, of the ion exchange reaction was determined to be 27 s^?1 by the stopped flow spectroscopic method. The anodic peak of the pre-deposited iodide ion on the electrode surface was observed at +0.54 V in a cyclic voltammogram. Various experimental parameters such as pH, deposition time, temperature, and electrode composition were optimized to analyze the iodide ion employing linear sweep and differential pulse voltammetry. With the exception of thiosulfate ions, inorganic anions did not interfere with the determination of the iodide ion. Using linear sweep voltammetry, a calibration curve was attained over the concentration ranges of the iodide ion from 1.0×10^?4–2.5×10^?6 M at the deposition time of 10 min, with the detection limit determined as 1.0×10^?6 M. Using differential pulse voltammetry, the logarithmic linear response range for the iodide ion was between 10^?6 and 10^?8 M, and the detection limit was 1.0×10^?8 M. This method was evaluated by analyzing the iodide ion content in a commercial disinfectant.     

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.     

Electrochemical investigations and morphology of poly(4,9-dihydro-o-benzenonaphtho[2,3-c]pyrrole) and poly(acenaphtho[1,2-c]pyrrole)

The electrochemical characteristics and morphology of poly(4,9-dihydro-o-benzenonaphtho[2,3-c]pyrrole) (PDBNP) and poly(acenaphtho[1,2-c]pyrrole) (PANP) films prepared by controlled potential oxidation in acetonitrile containing 0.002 M monomer and 0.1 M tetrabutylammonium perchlorate (TBAP) have been studied. The impedance of PDBNP and PANP films coated onto glassy carbon electrodes measured in 0.1 M TBAP shows that the ionic conductivities of these two films increase with increasing electrode potential (oxidation level) as ClO₄^? ions are incorporated. It is concluded that anion transport is primarily responsible for the ionic conductivities. PANP has a 45° Warburg region at all electrode potentials. However, for PDBNP, the 45° Warburg region is seen only at low electrode potentials. The difference in the mode of charge transport shows that the value of electronic resistance of PDBNP at higher doping levels is similar to the ionic resistance, but for PANP, the electronic resistance is much smaller than the ionic resistance at all doping levels. The apparent electrochemical reversibility was seen to be higher for PDBNP than for PANP from cyclic voltammetry. Evidence for this interpretation is that the ionic conductivities increase dramatically with electrode potentials for PDBNP, indicating that the counterion ClO₄^? moves more easily in PDBNP than PANP. The higher low-frequency capacitance obtained from impedance spectroscopy for PANP is discussed in the light of in situ atomic force microscopy (AFM) observation of the film structure morphology.     

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.     

Electrochemical study of mefexamide at glassy-carbon electrodes and its determination in urine by differential pulse voltammetry

The electrochemical oxidation of mefexamide N-[2-(diethylamino)ethyl]-2-(4-methoxyphenoxy)acetamide was investigated using cyclic, linear scan and rotating disk voltammetry at glassy-carbon electrodes. The value of pK_a (9.01) was determined by the potentiometric method. In cyclic voltammetry, in neutral media, the compound shows two electrochemical irreversible oxidation peaks (both 2e^?), Ox1 and Ox2. A new redox couple Red3/Ox3, formed as a result of the oxidation Ox1 peak, followed for an irreversible chemical reaction, appears on the reverse negative sweep. In acidic media, only the Ox1 peak was observed. The most defined peaks were obtained in 0.040 M Britton–Robinson buffer (pH 6.0) and 0.010 M sulfuric acid with 0.10 M sodium sulfate. The Ox1 and Ox2 peak currents were diffusion-controlled, showing an adsorption effect for low mefexamide concentrations (1.0×10^?4 M) and calibration plots at 20 mV s^?1, being linear in the range 5.0×10^?5–5.0×10^?4 M. The limiting currents in a rotating disk electrode were mass transport controlled for rotation speeds lower than 3000 rpm. The anodic charge transfer coefficient, the mass-transport rate constant, the diffusion coefficient and the charge-transfer conditional constant were determined. Also, a method for the electrochemical determination of mefexamide in human urine was developed using differential pulse voltammetry, in 0.040 M Britton–Robinson buffer (pH 6.0), being extracted with dichloromethane. The standard addition method was applied. The detection limit was 0.8 μg of mefexamide per milliliter of urine. The statistical validation reveals that the method is free from significant systematic errors.