Determination of p-nitrophenol on carbon paste electrode modified with a nanoscaled compound oxide Mg(Ni)FeO

A novel electrochemical sensor for the determination of p-nitrophenol (PNP) was fabricated with the nanoscaled composite oxide Mg(Ni)FeO-modified carbon paste electrode (CPE), and its electrocatalytic performances were investigated using the cyclic voltammogram and differential pulse voltammetry techniques. The influential factors were optimized such as the mass ratio of Mg(Ni)FeO to graphite, the pH value of buffer solution and the accumulation time at open circuit. The indirect oxidation peak current of PNP was found to be proportional to its concentration between 2.0 × 10^?6 and 2.0 × 10^?4 M on the proposed sensor Mg(Ni)FeO/CPE under the optimal condition (10 % Mg(Ni)FeO/graphite, pH 5.0 HAc–NaAc, 120 s quiescence). The sensor Mg(Ni)FeO/CPE exhibited a high sensitivity of 811 μA mM^?1 cm^?2 and a low detection limit of 0.2 μΜ (S/N– = 3) for PNP detection, and got satisfactory results when it was applied to determine PNP in real samples. The results demonstrate that Mg(Ni)FeO/CPE based on the nanomaterial Mg(Ni)FeO with high specific area and mesoporous structure could be employed as an electrochemical sensor for PNP determination with simplicity, low cost, good selectivity, repeatability, and stability.     

High electrocatalysis of ethylene glycol oxidation based on nickel particles electrodeposited into poly (m-toluidine)/Triton X-100 composite

Poly (m-toluidine) (PMT) was formed by successive cyclic voltammetry in a monomer solution containing Triton X-100 (TX-100) at the surface of carbon paste electrode (CPE). Nickel was then incorporated into the polymer by electrodeposition of Ni(II) from NiSO₄ acidic solution. The electrochemical behavior of this modified electrode (Ni/PMT(TX-100)/MCPE) was investigated in the electrooxidation of ethylene glycol (EG) using cyclic voltammetry and chronoamperometry techniques. Among the electrodes [Ni/PMT(TX-100)/MCPE, Ni/PMT/MCPE, Ni/MCPE, PMT(TX-100)/MCPE, and CPE] used in this study, Ni/PMT(TX-100)/MCPE showed the most effective catalytic activity. The effects of various parameters such as film thickness, electrodepositing time, TX-100 concentration, MT concentration, and EG concentration were investigated on the electrocatalytic oxidation of EG at the surface of Ni/PMT(TX-100)/MCPE. The catalytic rate constant (k) for EG oxidation was also calculated to be 2.1 × 10⁶ cm³ mol^?1 s^?1 using a chronoamperometric method.     

A simple and sensitive electroanalytical determination of anxiolytic buspirone hydrochloride drug based on multiwalled carbon nanotubes modified electrode

In the present study, a simple and sensitive buspirone hydrochloride (BPH) sensor was developed based on multiwalled carbon nanotubes (MWCNT) modified electrode. The modified electrode was characterized using transmission electron microscopy and electrochemical impedance spectroscopy. The MWCNT modified electrode showed an enhanced oxidation peak current response toward BPH than unmodified electrode. The oxidation peak potential of BPH at modified electrode was 0.85, which was quite lower than that of bare electrode (0.88 V). The BPH was successfully determined at modified electrode using different electrochemical methods, such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometry. The good sensitivity and linear range response of BPH were obtained using amperometry when compared with other methods employed in this study (CV and DPV). The modified electrode displayed the electro-oxidation of BPH in the linear response from 0.5 to 99.5 μM with the sensitivity of 16.49 μA μM^?1 cm^?2. The limit of detection was calculated as 0.22 μM. In addition, the modified electrode exhibited a good repeatability and repeatability with acceptable stability.     

Preparation of polypyrrole/ferrocyanide films modified carbon paste electrode and its application on the electrocatalytic determination of ascorbic acid

Functionalized polypyrrole film were prepared by incorporation of (Fe(CN)₆)⁴⁻ as doping anion, during the electropolymerization of pyrrole onto a carbon paste electrode (CPE) in aqueous solution by using potentiostatic method. The electrochemical behavior of the (Fe(CN)₆)³⁻/(Fe(CN)₆)⁴⁻ redox couple in polypyrrole was studied by cyclic voltammetry and double step potential chronoamperometry methods. In this study, an obvious surface redox reaction was observed and dependence of this reaction on the solution pH was illustrated. The electrocatalytic ability of polypyrrole/ferrocyanide films modified carbon paste electrode (Ppy/FCNMCPEs) was demonstrated by oxidation of ascorbic acid. It has been found that under optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such electrode occurs at a potential about 540 mV less positive than unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and catalytic reaction rate constant, k_h′, were also determined by using various electrochemical approaches.The catalytic oxidation peak current showed a linear dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range of 4.5×10⁻⁴ to 9.62×10⁻³ M of ascorbic acid with a correlation coefficient of 0.9999. The detection limit (2σ) was determined as 5.82×10⁻⁵ M.     

Self-assembly of Ag-phosphotungstic acid composite nanoparticles on a modified ITO electrode for the electrochemical detection of 4-chlorophenol

Ag-phosphotungstic acid composite nanoparticles (Ag-PTA NPs) were synthesized by the reduction of silver nitrate with UV-irradiation in a PTA solution, followed by the assembly of the nanoparticles onto chitosan (CTS)-modified ITO-glass to be used for the electrochemical detection of 4-chlorophenol (4-CP). This modified electrode considerably increased the oxidation signals of 4-CP, which demonstrated its high electrocatalytic activity. The oxidation of 4-CP on the modified electrode is a reversible process controlled by surface absorption. The results of differential pulse voltammetry (DPV) showed that the peak current is linear with the 4-CP concentration in the range from 1 μM to 0.4 mM, with a correlation coefficient of 0.999, a response sensitivity of 0.1247 μA/μM, and a detection limit of 0.34 μM (S/N = 3). These results, combined with the electrode’s good reproducibility, stability, and anti-interference performance, certainly make the Ag-PTA/CTS/ITO electrode a potential electrochemical sensor for the detection of chlorophenols.     

Voltammetric Response and Determination of an Anti-Inflammatory Drug at a Cationic Surfactant-Modified Glassy Carbon Electrode

Electrochemical oxidation of thiosalicylic acid in the presence of cationic surfactant, cetyl trimethylammonium bromide (CTAB), at a glassy carbon electrode was investigated. The electrochemical response of a modified sensor towards thiosalicylic acid determination was studied by the means of cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry (DPV). The liquid phase oxidation of thiosalicylic acid in the presence of CTAB leads to a notable enhancement in the peak current and a lowering of the peak potential. The electrochemical process was observed to be adsorption-controlled, irreversible and involves oxidation of one electron. Effects of anodic peak potential (E _p), anodic peak current (I _pa) and heterogeneous rate constant (k ⁰) were calculated. The linear response was obtained in the range of 1.0 µM–1.0 mM with a detection limit of 113 nM.     

Synthesis of 3D cubic of Eu3+/Cu2O with clover-like faces nanostructures and their application as an electrochemical sensor for determination of antiretroviral drug nevirapine

In this experiment, an original three-dimensional (3D) cubic of europium (Eu) ³⁺/cuprous oxide (Cu₂O) with clover-like face-centered nanostructures (Eu³⁺/Cu₂O CLFNs) was successfully synthesized to determine nevirapine (C₁₅H₁₄N₄O), using electrochemical methods. The surface morphology of the Ns was correspondingly identified through different techniques, including energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In this sense, the synergistic influence of the Eu³⁺/Cu₂O CLFNs enhanced the electrocatalytic capability of the electrode via a modified glassy carbon (GC) and raised the active site. Employing various approaches, the modified electrode was then analyzed through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Moreover, kinetic parameters and electrochemical ones were estimated by means of voltammetric methods. For the determination of nevirapine applying the Eu³⁺/Cu₂O CLFNs/GC electrode (GCE), differential pulse voltammetry (DPV) was further utilized. Under optimized conditions, the range of linear responses was between 0.01 and 750.0 μM with the limit of detection (LOD) of 3.6 nM, whereas the recommended sensor sensitivity was equal to 0.1244 μA/μM. The response time of approximately 3.5 min and the reproducibility (inter- and intra-electrode reproducibility of 2.26% and 1.51%, respectively) were subsequently achieved. It was concluded that sensors have been thus far exploited to determine nevirapine in real samples with favorable outcomes, indicating that electrocatalysis modifier can be assumed as one of appropriate catalysts.     

Gold nanoparticle–polypyrrole composite modified TiO<Subscript>2</Subscript> nanotube array electrode for the amperometric sensing of ascorbic acid

Titanium dioxide (TiO₂) nanotubes were fabricated by anodisation of titanium foil in 0.15 M ammonium fluoride in an aqueous solution of glycerol (90 % v/v). Electropolymerisation of pyrrole and deposition of gold nanoparticles on to the TiO₂ nanotube array electrode were carried out by cyclic voltammetry (CV). Electrochemical characterization of the sensor was performed by CV and electrochemical impedance spectroscopy. The morphology of the electrode was studied after every step of modification using field emission scanning electron microscope and atomic force microscope. The sensor was tested for AA and other biomolecules in phosphate buffered saline solution of pH 7 using CV, differential pulse voltammetry and amperometry. The sensor exhibited very high sensitivity of 63.912 μA mM^?1 cm^?2 and excellent selectivity to ascorbic acid (AA) in the presence of other biomolecules such as uric acid, dopamine, glucose and para-acetaminophen. It also showed very good linearity (R = 0.9995) over a wide range (1 μM–5 mM) of detection. The sensor was tested for AA in lemon and found its concentration to be 339 mg ml^?1.     

Effect on properties of PVDF-HFP based composite polymer electrolyte doped with nano-SiO2

Various kinds of nano-SiO₂ using different catalysts were obtained and characterized by scanning electron microscope (SEM) technique. The results showed that the nano-SiO₂ using NH₃·H₂O as catalyst presented the best morphology. Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) based composite polymer electrolyte (CPE) membranes doped with different contents of nano-SiO₂ were prepared by phase inversion method. The as-prepared CPE membranes were immersed into 1.0 M LiPF₆-EC/DMC/EMC electrolytes for 0.5 h to be activated. The physicochemical and electrochemical properties of the CPEs were characterized by SEM, X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) techniques. The results indicate that the CPEs doped with 10 % nano-SiO₂ exhibit the best performance. SEM micrographs showed that the CPE membranes have uniform surface with abundant interconnected micro-pores, and the uptake ratio was up to 104.4 wt%. EIS and LSV analysis also showed that the ionic conductivity at room temperature and electrochemical stability window of the modified membrane can reach 3.372 mS cm^?1 and 4.7 V, respectively. The interfacial resistance R _i was 670 Ω cm^?2 in the first day, then increased to a stable value of about 850 Ω cm^?2 in 10 days storage at room temperature. The Li/As-fabricated CPEs/LiCoO₂ cell also showed good charge–discharge performance, which suggested that the prepared CPE membranes can be used as potential electrolytes for lithium ion batteries.     

Aniline pentamer-based electroactive polyimide prepared from oxidation coupling polymerization for electrochemical sensing application

This article details electrochemical investigations of carbon paste electrode (CPE) modified with electroactive polyimide (EPI) as ascorbic acid sensor (vitamin C, AA). EPI, with aniline-pentamer-based in the main chain, was synthesized from oligoaniline and p-phenylenediamine by oxidative coupling polymerization. The well-defined molecular structure of the oligoaniline and EPI was confirmed by LC-Mass, ¹H NMR and FTIR spectroscopy. The in-situ chemical oxidation of the reduced form of soluble, electroactive poly(amic acid) (EPAA) in N-methyl-2-pyrrolidone was monitored by UV–Visible absorption spectra. Moreover, the electroactivity of the EPAA and EPI were evaluated by performing electrochemical cyclic voltammetry studies. A linear relationship between the concentration of AA added and the change of peak current obtained, as shown by the linear calibration curve of the amperometric response of the CPE modified with EPI sensor to the concentration of AA (R² = 0.996, n = 15). The limit of quantitation measured was 32.2 μM and the limit of detection for the EPI–CPE was estimated 9.6 μM at signal/noise (S/N) of 3.     

Electrochemical determination of malachite green at graphene quantum dots–gold nanoparticles multilayers–modified glassy carbon electrode

A graphene quantum dots–gold nanoparticles–modified glassy carbon electrode was used to investigate the electrochemical behaviors of malachite green (MG). Cyclic voltammetry curves of MG at the modified electrode exhibited a pair of quasi-reversible adsorption-controlled redox peaks at 0.502 V (E _pa) and 0.446 V (E _pc) in a 0.05 mol L^?1 H₂SO₄ solution. Under the optimal conditions, by using differential pulse voltammetry as the detection method, a linear relationship was obtained between the oxidation peak current and the MG concentration in the range of 4.0 × 10^?7 to 1.0 × 10^?5 mol L^?1 with the detection limit as 1.0 × 10^?7 mol L^?1 (signal-to-noise ratio of 3). The modified electrode was applied in the determination of MG in fish samples, and the results were satisfactory with recoveries from 96.25 to 98.00 %. Furthermore, the modified electrode showed very good reproducibility and stability.     

Square wave voltammetric determination of methiocarb insecticide based on multiwall carbon nanotube paste electrode

Cyclic voltammogram of methiocarb in 0.1 M H₂SO₄ exhibited an irreversible anodic peak at about +1285 mV versus Ag/AgCl. Electro-oxidation and determination of methiocarb in spiked soil, river water and agrochemical formulation were realized on a newly prepared carbon-nanotube paste electrode by applying square wave voltammetry (SWV). The dE _p /dpH value indicated that the oxidation mechanism involved the coupling of H⁺ with the oxidation process. The peak signals were linearly related to methiocarb concentration in the range of 1.5–59.1 mgL^?1 with a detection limit of 0.45 mgL^?1. The accuracy and selectivity of the proposed method were shown by calculating the recoveries of methiocarb from soil, river water and pesticide formulation Mesurol^®. The calculated percent recoveries for soil and river water samples spiked with 30.0 μg g^?1 and 40.0 μg mL^?1 levels were 99.3 ± 1.2 and 98.5 ± 0.3 at 95 % confidence limit, respectively.     

Preparation and electrocatalytic oxidation properties of a nickel pentacyanonitrosylferrate modified carbon composite electrode by two-step sol-gel technique: improvement of the catalytic activity

The sol-gel technique was used to construct nickel pentacyanonitrosylferrate (NiPCNF) modified composite ceramic carbon electrodes (CCEs). This involves two steps: forming a CCE containing Ni powder and then immersing the electrode into a sodium pentacyanonitrosyl-ferrate solution (electroless deposition). The cyclic voltammograms of the resulting surface modified CCE under optimum conditions show a well-defined redox couple due to the [Ni^IIFe^III/II(CN)₅NO]^0/−1 system. The electrochemical properties and stability of the modified electrode were investigated by cyclic voltammetry. The apparent electron transfer rate constant (k_s) and transfer coefficient (α) were determined by cyclic voltammetry being about 1.1 s⁻¹ and 0.55, respectively. Sulfite has been chosen as a model to elucidate the electrocatalytic ability of NiPCNF-modified CCE prepared by one- or two-step sol-gel technique. The modified electrode showed excellent electrocatalytic activity toward the SO₃²⁻ electro oxidation in pH range 3-9 in comparison with CCE modified by homogeneous mixture of graphite powder, Ni(NO₃)₂ and Na₂[Fe(CN)₅NO] (one-step sol-gel technique). Sulfite was determined amperometrically at the surface of this modified electrode in pH 7. Under the optimized conditions the calibration curve is linear in the concentration range 2 μM to 2.0 mM. The detection limit (signal-to-noise is 3) and sensitivity are 0.5 μM and 13.5 nA/μM. The modified carbon ceramic electrode containing nickel pentacyanonitrosylferrate shows good repeatability, short response time, t (90%) <2 s, long-term stability (3 months), and it is renewed by simple mechanical polishing and its immersing in Na₂[Fe(CN)₅NO] solution. The advantages of the SO₃²⁻ amperometrically detector based on the nickel pentacyanonitrosylferrate-doped CCE is high sensitivity, inherent stability at wide pH range, excellent catalytic activity and less expense and simplicity of preparation. This sensor can be used as amperometric detector in chromatographic instruments.     

Electrochemical sensing of NADH on NiO nanoparticles-modified carbon paste electrode and fabrication of ethanol dehydrogenase-based biosensor

In this work, an electrochemical β-nicotinamide adenine dinucleotide (NADH) sensor based on a carbon paste electrode modified with nickel oxide nanoparticles (NiONPs) was developed. The key highlights of this work are ease of preparation of the NiONPs-modified carbon paste electrode (NiONPs/MCPE), and its high sensitivity to NADH. The electrochemical characterization of NiONPs/MCPEs was performed via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical oxidation response of NADH was investigated by differential pulse voltammetry and chronoamperometry. The results indicated that the electrocatalytic effects of NiONPs on the response current of NADH significantly facilitated the electron transfer and improved the performance of the biosensor. Compared to bare carbon paste electrode (BCPE), the oxidation potential was shifted toward more negative potentials and the oxidation current was increased remarkably. Under optimum conditions, NADH could be detected in the range from 1.0 × 10^?4 to 1.0 mmol L^?1 with lower detection limit (0.05 μmol L^?1). The proposed NADH sensor demonstrated fast and reproducible response. Furthermore, an ethanol biosensor was prepared using NiONPs and NAD⁺-dependent alcohol dehydrogenase enzyme giving linear responses over the concentration range of 1.6 and 38 mmol L^?1 of ethanol.     

Electrolyte type and concentration effects on poly(3-(2- aminoethyl thiophene) electro-coated on glassy carbon electrode via impedimetric study

In this study, 3-(2-Aminoethyl thiophene) (2AET) monomer was electropolymerized on glassy carbon electrode (GCE) using various electrolytes (lithium perchlorate (LiClO₄), sodium perchlorate (NaClO₄), tetrabutyl ammonium tetra fluoroborate (TBABF₄) and tetraethyl ammonium tetra fluoroborate (TEABF₄) in acetonitrile (CH₃CN) as solvent. Poly(3-(2-aminoethyl thiophene) (P(2AET))/GCE was characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance spectrophotometry (FTIR-ATR), scanning electron microscopy, energy dispersive X-ray analysis (EDX), and electrochemical impedance spectroscopy (EIS) techniques. The electrochemical impedance spectroscopic results were given by Nyquist, Bode-magnitude, Bode-phase, capacitance and admittance plots. The highest low frequency capacitance (C _LF) value obtained was 0.65 mF cm^?2 in 0.1 M LiClO₄/CH₃CN for the initial monomer concentration of 1.5 mM. The highest double layer capacitance (C _dl = ~0.63 mF cm^?2) was obtained in 0.1 M LiClO₄/ACN for [2AET]₀ = 0.5, 1.0 and 1.5 mM. The maximum phase angles (θ = 76.1^o at 26.57 Hz) and conductivity (Y″ = 3.5 mS) were obtained in TEABF₄/ACN for [2AET]₀ = 0.5 and 1.0 mM, respectively. An equivalent circuit model of R(Q(R(Q(R(CR))))) was simulated for different electrolytes (LiClO₄, NaClO₄, TBABF₄ and TEABF₄)/P(2AET)/GCE system. A good fitting was obtained for the calculated experimental and theoretical EIS measurement results. The electroactivity of P(2AET)/GCE opens the possibility of using modified coated electrodes for electrochemical micro-capacitor electrodes and biosensor applications.     

Electrocatalytic Oxidation of Formaldehyde onto Carbon Paste Electrode Modified with Nickel Decorated Nanoporous Cobalt‐Nickel Phosphate Molecular Sieve for Fuel Cell

Nanoporous cobalt‐nickel phosphate VSB‐5 molecular sieve (CoVSB‐5) was synthesized by conventional heating for 48 h in the presence of (2‐hydroxyethyl) trimethylammonium hydroxide as template. Then, a novel, cheap and efficient catalyst was developed for formaldehyde electrooxidation by decorating Ni²⁺ ions on the surface of CoVSB‐5 modified carbon paste electrode (CoVSB‐5/CPE). The electrochemical behavior of the Ni‐CoVSB‐5/CPE electrode towards the formaldehyde oxidation was evaluated by cyclic voltammetry (CV) as well as chronoamperometry methods. An oxidation peak was observed at 0.60 V in 0.1M NaOH solution for electrocatalytic oxidation of formaldehyde with EC′ mechanism. It has been observed that CoVSB‐5 at the surface of CPE can improve catalytic efficiency of the dispersed nickel ions toward oxidation of formaldehyde. The values of electron transfer coefficient, the mean value of catalytic rate constant and diffusion coefficient for formaldehyde and redox sites were obtained to be 0.66, 1.80 × 10⁵ cm³ mol⁻¹ s⁻¹ and 3.62 × 10⁻⁴ cm² s⁻¹, respectively. Obtained results from cyclic voltammetry (CV) and chronoamperometry techniques specified that the electrode reaction is a diffusion‐controlled process. The good catalytic activity, high sensitivity, good selectivity and stability and easy in preparation rendered the Ni‐CoVSB‐5/CPE to be a capable electrode for formaldehyde electrooxidation.     

A nickel hexacyanoferrate and poly(1-naphthol) hybrid film modified electrode used in the selective electroanalysis of dopamine

A mixed-valent nickel hexacyanoferrate and poly(1-naphthol) hybrid (NiHCF–PNH) film was prepared on a gold (Au) electrode by a galvanostatic method, which led to stable and homogeneous hybrid film. The film was characterized using scanning electronic microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. This electrode showed excellent catalytic properties toward dopamine (DA) detection, using cyclic voltammetry and differential pulse voltammetry methods. The electrocatalytic oxidations of DA at different electrodes, such as a bare Au electrode or a poly(1-naphthol)/Au-, or NiHCF–PNH/Au-modified electrode, were investigated in a phosphate buffer solution (pH 7). Interestingly, the NiHCF–PNH-modified electrode facilitated the oxidation of DA, but it did not responded to other electroactive biomolecules, such as ascorbic acid and uric acid_. The DA electrochemical sensor exhibited a linear response from 0.1 to 4.3 μM (R² = 0.9984) and from 4.3 to 9.6 μM (R² = 0.9969), with a detection limit of 2.1 × 10^?8 M, and a short response time (3 s) for DA determination. In addition, the NiHCF–PNH-modified electrode exhibited distinct advantages by its simple preparation, specificity, and stability.     

Ag nanowires and its application as electrode materials in electrochemical capacitor

Silver nanowires were synthesized on a large scale by using anodic aluminum oxide (AAO) film as templates and serving ethylene glycol as reductant. Their morphological and structural characterizations were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED). The electrochemical properties of silver nanowires as electrode materials for electrochemical capacitors were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge technique in 6 M KOH aqueous electrolyte. The Ag₂O/Ag coaxial nanowires were formed by the incomplete electrochemical oxidation during the charge step. The maximum specific capacitance of 987 F g^?1 was obtained at a charge–discharge current density of 5 mA cm^?2.     

Electrochemistry and determination of epinephrine using a mesoporous Al-incorporated SiO2 modified electrode

The potential application of Al-incorporated mesoporous SiO₂ (denoted as Al-MCM-41) in electrochemistry as a novel electrode material was investigated. The peak currents of K₃[Fe(CN)₆] remarkably increase and the peak potential separation obviously decreases at the mesoporous Al-MCM-41 modified carbon paste electrode (CPE). These phenomena suggest that the mesoporous Al-MCM-41 modified CPE possesses larger electrode area and electron transfer rate constant. Furthermore, the electrochemical behavior of epinephrine (EP) was investigated in different supporting electrolytes such as 0.01 mol L⁻¹ HClO₄ and pH 7.0 phosphate buffer. It is found that the mesoporous Al-MCM-41 modified CPE exhibits catalytic ability to the oxidation of EP due to remarkable peak current enhancement and negative shift of peak potential. The electrochemical oxidation mechanism was also discussed. Finally, a novel electrochemical method was proposed for the determination of EP, which used to determine EP in urine samples.     

Electrochemical characterization of cetyltrimethyl ammonium bromide modified carbon paste electrode and the application in the immobilization of DNA

A cetyltrimethyl ammonium bromide modified carbon paste electrode (CTAB/CPE) was developed in this work based on the surface modification method. The improved electrochemical response of K₄Fe(CN)₆ at this electrode indicated that CTAB could change the surface property of carbon paste electrodes (CPEs), which was demonstrated by the electrochemical impedance spectroscopy (EIS). In 0.1 mM [Fe(CN)₆]^3−/4−, a low exchange current (i₀) of 2.72×10⁻⁷ A at bare CPE was observed while that at CTAB/CPE was 6.79×10⁻⁵ A. The effect of CTAB concentration on the electrode quality revealed that CTAB formed a compact monolayer on the electrode surface with high density of positive charges directed outside the electrode. This electrode showed strong accumulation ability toward Fe(CN)₆⁴⁻ and can also accumulate Co(phen)₃²⁺ by the adsorption of the organic ligands in the hydrophobic area of the monolayer. The electrode was applied to the immobilization of DNA, which was characterized by the isotherm adsorption of Co(phen)₃²⁺.