Electrochemical determination of vitamin C in the presence of uric acid by a novel TiO_2 nanoparticles modified carbon paste electrode

The electrochemical behavior of vitamin C（ascorbic acid or AA） is investigated on the surface of a carbon-paste electrode modified with TiO2 nanoparticles and 2,2＇-（1,2 butanediylbis（nitriloethylidyne））-bis-hydroquinone（BBNBH）.The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of AA,leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction.This modified electrode exhibits well-separated oxidation peaks for AA and uric acid（UA）.The modified electrode is successfully applied for the accurate determination of AA in pharmaceutical preparations.

基于纳米结构的电化学传感器用于伏安法测定苄丝肼、尿酸和叶酸(英文)

A carbon paste electrode modified with carbon nanotubes and ferrocene was fabricated.An electrochemical study of the modified electrode and an investigation into its efficiency for the electrocatalytic oxidation of benserazide,uric acid and folic acid were undertaken.The electrode was also used to study the electrocatalytic oxidation of benserazide using cyclic voltammetry,chronoamperometry,and square wave voltammetry(SWV).We found that the oxidation of benserazide at the surface of the modified electrode occurs at a potential about 285 mV lower than that of unmodified carbon paste electrode.SWV gave a linear dynamic range from 8.0×10-7 to 7.0×10 4 mol/L.The detection limit was 1.0×10-7 mol/L for benserazide.This modified electrode was used for the determination of benserazide,uric acid,and folic acid in an urine sample.

对乙酞氨基酚和色氨酸存在下采用改进的碳纳米管糊电极伏安法测定抗坏血酸(英文)

A carbon paste electrode (CPE) modified with carbon nanotubes and 5‐amino‐3',4'‐dimethyl‐ bi‐ phenyl‐2‐ol (5ADB) is prepared. Under the optimum pH of 7.0, the oxidation of ascorbic acid (AA) on the modified CPE occurs at a potential about 280 mV less positive than that on the unmodified CPE. Some kinetic and thermodynamic parameters for electrocatalytic oxidation of AA, including electron transfer coefficient (α = 0.58) and diffusion coefficient (D = 2.2 × 10-6 cm2/s), are also determined. AA, acetaminophen (AC), and tryptophan (TRP) were detected simultaneously using the modified CPE. The peak potentials recorded using the modified CPE in phosphate‐buffered solution at pH 7.0 were 265, 465, and 780 mV for AA, AC, and TRP, respectively. The modified CPE was successfully used to determine the concentrations of AA, AC, and TRP in real samples.

苯甲酰二茂铁修饰碳纳米管糊电极电催化测量蛋氨酸浓度(英文)

A benzoylferrocene modified multi‐wall carbon nanotube paste electrode for the measurement of methionine (MET) concentration is described. MET electrochemical response characteristics of the modified electrode in a phosphate buffer solution of pH 7.0 were investigated by cyclic voltammetry, square wave voltammetry, and chronoamperometry. Under optimized conditions, the square wave voltammetric peak current of MET increased linearly with MET concentration in the range of 1.0×107 to 2.0×104 mol/L. The detection limit was 58.0 nmol/L MET. The diffusion coefficient (D=5.62×106cm2/s) and electron transfer coefficient (α=0.4) for MET oxidation were also determined. The sensor was successfully applied for the measurement of MET concentration in human urine.

Electrocatalytic determination of L-cysteine using a modified carbon nanotube paste electrode:Application to the analysis of some real samples

The electrooxidation of L-cysteine（L-Cys） was studied using a benzoylferrocene（BF） modified multi-wall carbon nanotube paste electrode（BFCNPE） using cyclic voltammetry（CV）,square wave voltammetry（SWV） and chronoamperometry（CHA）.Under optimum pH in CV the oxidation of L-Cys occurs at a potential about 215 mV less positive than that at the surface of unmodified carbon paste electrode.The catalytic oxidation peak currents were dependent on the L-Cys concentration and a linear calibration curve was obtained in the range 0.7-350.0 mmol/L of L-Cys with SWV method.The detection limit（3s） was determined as 0.1 mmol/L.This method was also used for the determination of L-Cys in some real samples.

Voltammetric determination of venlafaxine as an antidepressant drug employing Gd_2O_3 nanoparticles graphite screen printed electrode

Graphite screen printed electrode modified with Gd_2 O_3 nanoparticles(Gd_2 O_3/SPE) was developed for the determination of venlafaxine(VF). The Gd_2 O_3 nanoparticles were thoroughly characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analyses. To study the electrochemical behaviour of venlafaxine cyclic voltammetry(CV), chronoamperometry(CHA)and differential pulse voltammetry(DPV) were employed. These studies reveal that the oxidation of venlafaxine is facilitated at Gd_2 O_3/SPE. After optimization of analytical conditions, analysis of venlafaxine using the modified electrode in 0.1 mol/L PBS(pH 7.0) demonstrates that the peak currents corresponding to venlafaxine vary linearly with its concentration in the range of 5.0 ×10^(-6)-9.0 × 10^(-4) mol/L. The detection limit(S/N = 3) of 2.1 × 10^(-7) mol/L is obtained for venlafaxine using DPV. The prepared modified electrode benefits from advantages such as simple preparation method, high sensitivity and low detection limit.Moreover, the evaluation of practical applicability of this proposed method is successful in the identification of venlafaxine in pharmaceutical formulations, urine and water samples.

Simultaneous determination of cysteamine and folic acid in pharmaceutical and biological samples using modified multiwall carbon nanotube paste electrode

A carbon paste electrode（CPE） chemically modified with multiwall carbon nanotubes and ferrocene（FC） was used as a selective electrochemical sensor for the simultaneous determination of trace amounts of cysteamine（CA） and folic acid（FA）.This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of CA.The peak current of differential pulse voltammograms of CA and FA increased linearly with their concentration in the ranges of 0.7-200μmol/L CA and 5.0- 700μmol/L FA.The detection limits for CA and FA were 0.3μmol/L and 2.0μmoI/L,respectively.The diffusion coefficient（D） and transfer coefficient（α） of CA were also determined.These conditions are sufficient to allow determination of CA and FA both individually and simultaneously.

Voltammetric determination of isoproterenol using a 5-amino-2',4'-dimethoxybiphenyl-2-ol modified carbon nanotube paste electrode

A new electrochemical sensor for determination of isoproterenol （IP） is described. The sensor is based on carbon paste electrode （CPE） modified with 5-amino-2＇,4＇-dimethoxybiphenyl-2-ol （5ADMB） and takes the advantages of carbon nanotubes （CNTs）. Under the optimum pH of 7.0, the oxidation of IP occurs at a potential about 210 mV less positive than that of the unmodified CPE. The oxidation currents increased linearly with two concentration intervals oflP, one is 0.09 to 20.0 μ mol/L and, the other is 20.0 to 400.0 μmol/L. The detection limit （3or） obtained by square wave voltammetry （SWV） was 39.0 μmol/L. The practical application of the modified electrode was demonstrated by determining IP in IP ampoule, urine and human blood serum samples.

Electrocatalytic determination of epinephrine and uric acid using a novel hydroquinone modified carbon paste electrode

A sensitive and selective electrochemical method for the determination of epinephrine（EP） was developed using a modified carbon paste electrode（MCPE） with 2,2＇-[3,6-dioxa-1,8-octanediylbis（nitriloethylidyne）]-bis-hydroquinone（DOH）.Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates.In differential pulse voltammetry,the modified electrode could separate the oxidation peak potentials of EP and uric acid（UA） present in the solution but at the unmodified CPE the peak potentials were indistinguishable.This method was also examined for determination of EP in EP injection.

Stripping voltammetric determination of Cd(Ⅱ)based on multiwalled carbon nanotube functionalized with 1-(2-pyridylazo)-2-naphthol

The present work has focused on the modification of multiwalled carbon nanotube with a ligand,l-（2-pyridylazo）-2-naphthol, and its potential application for the development of a new,simple and selective modified glassy carbon electrode for stripping voltammetric determination of Cd（Ⅱ）.The analytical curve for Cd（Ⅱ） ions covered the linear range varying from 0.8 up to 220.4μgL^（-1）.The limit of detection was found to be 0.1μgL^（-1）,while the relative standard deviation（RSD） at 50.0μgL^（-1） was 1.8%（n=5）.This modified electrode was successfully applied for determination of Cd（Ⅱ） in some water samples.

Application of graphite screen printed electrode modified with dysprosium tungstate nanoparticles in voltammetric determination of epinephrine in the presence of acetylcholine

The current work focuses on the development of a sensitive and selective electrochemical device based on a graphite screen printed electrode modified with Dy2（WO4）3 nanoparticles（DWO/SPE） for the analysis of epinephrine in samples also containing acetylcholine. The study proves that the sensor has excellent electron-mediating behavior in the oxidation of epinephrine in a 0.1 mol/L phosphate buffer solution（PBS）（pH 7.0）. The application of the DWO/SPE in differential pulse voltammetry（DPV） is found to lead to distinct response for the oxidation of epinephrine and acetylcholine, with the potentials of the epinephrine and acetylcholine peaks（△Ep） to be 550 mV apart. The detection limits of the method for epinephrine and acetylcholine are 0.5 and 0.7 μmol/L（S/N = 3） and the responses are found to be linear in the concentration ranges of 1.0-900.0 μmol/L and 1.0-1200.0 μmol/L in a PBS buffer（pH = 7.0）respectively. The modified electrode was used for the detection of epinephrine and acetylcholine in real samples and found to produce satisfactory results. These results can be a proof that Dy2（WO4）3 nanoparticles can find promising applications in electrochemical sensors to be used for the analysis of（bio）chemical species.

Homogeneous and nanomolar detection of hydrazine by indigocarmine as a mediator at the surface of TiO_2 nanoparticles modified carbon paste electrode

The homogeneous electrocatalytic oxidation of hydrazine（HZ） has been studied by indigocarmine（IND） as a mediator at the surface of TiO_2 nanoparticles modified carbon paste electrode（TNMCPE）.Cyclic voltammetry was used to study the electrochemical behavior of IND at different scan rates.The voltammetric response of the modified electrode was linear against the concentration of HZ in the ranges of 3.0×l0^（-8）-7.0×10~6 mol/L with differential pulse voltammetry method.The detection limit（3σ） was determined as 27.3 nmol/L.To evaluate the applicability of the proposed method to real samples,the modified CPE was applied to the determination of HZ in water samples.