Sensitive Voltammetric Determination of Captopril Using a Carbon Paste Electrode Modified with Nano-TiO_2/Ferrocene Carboxylic Acid

A carbon paste electrode (CPE) modified with ferrocene carboxylic acid (FcCA) and TiO2 nanoparticles was constructed by incorporating TiO2 nanoparticles and ferrocene carboxylic acid into the carbon paste matrix. The electrochemical behavior of captopril (CAP) at the surface of the modified electrode was investigated using electroanalytical methods. The modified electrode showed excellent electrocatalytic activity for the oxidation of CAP in aqueous solutions at physiological pH values. Cyclic voltammetric curves showed that the oxidation of CAP at the surface of the modified electrode reduced its overpotential by more than 290 mV. The modified electrode was used for detecting captopril using cyclic voltammetry and square wave voltammetry techniques. A calibration curve in the range of 0.03 to 2400 μmol/L was obtained that had a detection limit of 0.0096 μmol/L (3?) under the optimized conditions. The modified electrode was successfully used for the determination of captopril in pharmaceutical and biological samples.

A Multiwall Carbon Nanotube-chitosan Modified Electrode for Selective Detection of Dopamine in the Presence of Ascorbic Acid

A novel multiwall carbon nanotube-chitosan modified electrode has been prepared.The modified electrode resolves the overlapping voltammetric response of dopamine and ascorbicacid into two well-defined peak by 212 mV. The mechanism of discrimination of dopamine fromascorbic acid is discussed. Dopamine can be determined selectively with the carbonnanotube-chitosan modified electrode. The electrode shows good sensitivity, selectivity andstability.

A selective voltammetric detection for dopamine using poly(gallic acid) film modified electrode

The electrochemistry behavior of dopamine was investigated by cyclic voltammetry and differential pulse voltammetry at a poly (gallic acid) film modified glassy carbon electrode.Two electrons and two protons participated in the diffusion-controlled electrocatalytic oxidation of dopamine with a diffusion coefficient of 2.186×10^(-5) cm^2/s.The interference of ascorbic acid with the determination of dopamine could be efficiently eliminated.This work provided a simple approach to selectively and sensitively de...

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.

Direct Electrochemistry of Cytochrome C on the Glassy Carbon Electrode Modified with 1-Pyrenebutyric Acid/MWNTs

With 1-Pymnebutyric acid （PBA） and multiwalled carbon nanotubes （MWNTs）, glassy carbon electrode modified was successfully prepared. In phosphate buffer solution （pH 7,0）, the direct electrochemistry of cytochrome C （Cyt C） was realized. In the cyclic voltammetry experiment two pairs of redox peaks ofCyt C were observed at 0.018 V and -0.314 V （vs. SCE）, respectively. The redox reaction at 0.018 V was diffusion controlled, while the redox reaction at -0.314 V was adsorption controlled.

Fabrication of Poly(Aspartic Acid)-Nanogold Modified Electrode and Its Application for Simultaneous Determination of Dopamine, Ascorbic Acid, and Uric Acid

A nanostructured polymer film incorporated gold nanoparticles modified electrode was fabricated. The fabrication process involved a previous electropolymerization of aspartic acid and followed by the eletrodeposition of gold nano-particles on the glassy carbon electrode. The resulting poly (aspartic acid)-nanogold modified electrode (PAA- nano-Au/GCE) was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectros-copy (EIS). A higher catalytic activity was obtained to electrocatalytic oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) due to the enhanced peak current and well-defined peak separations compared with three, bare GCE, PAA/GCE and nano-Au/GCE. Simultaneous determination of DA, AA, and UA were studied by voltammetry. The linear range of 5.0 × 10-7 - 1.0 × 10-4 M for DA, 5.0 × 10-6 - 2.0 × 10-3 M for AA and 5.0 × 10-6 - 1.0 × 10-3 M for UA was obtained. The detection limit was calculated for DA, AA and UA as being 6.5 × 10-8 M, 5.6 × 10-7 M and 3.0 × 10-7 M, respectively (S/N = 3). The practical application of the present modified electrode was demonstrated by the determination of DA, AA and UA in calf serum and fetal calf serum samples.

EASTMAN-AQ/Ni(II)MODIFIED ELECTRODE DETECTION OF CARBOHYDRATES AND AMINO ACIDS

An Eastman-AQ/Ni(II)chemically modified electrode(CME) produced by“double coating steps”deposition of Eastman-AQ/Ni(II) film and Ni(II)-coating crystalline species onto glassy carbon instead of metallic nickel electrode exhibited stable electrocatalytic oxidation of numerous ∝-hydrogen compounds including carbohydrates, amines and amino acids.Determination of glucose in FIA on the CME, the linear response concentration range was bstween 1.0×10^(-5) and 5.0×10^(-2) mol/L and the detection limit was 5.0×10^(-6)mol/L.The stability of the CME was adequate for routine quantitative application.

Studies on Zeolite Modified Electrode(Ⅰ)─Ascorbic Acid Sensor Based on Carbon Paste Electrode Containing Fe(Ⅲ)Y Zeolite

A new ascorbic acid sensor constituted of carbon paste and Fe(Ⅲ)Y zeolite was studied.The characters of the sensor such as linear range. potential window、apparen Michaelis constant、response time、stability and accuracy wee investigated. The experimental results indicate that the analytical performance of the sensor is satisfactory.

THE PREPARATION OF ISOPOLYMOLYBDIC ACID-POLYANILINE FILM MODIFIED ELECTRODE AND ITS CATALYTIC EFFECTS ON CHLORATE IONS

The preparation method of H_4MoO_(26)-polyaniline film modified electrode and its voltammetric behaviour are described. The modified electrode has high electrocatalytic activity on chlorate ions.

A New Thionine Modified Electrode by Anchorage to Bi-(2-aminoethyl)-aminodithiocarboxyl Acid Self-assembled Monolayers through Coordination with Cu^(2+#)

A new method for preparing chemically modified gold electrode by anchoring thionine to self-assembled bi - (2 -aminoethyl) -aminodithiocarboxyl acid(BANTC) monolayers through coordination with Cu2+ is described. This thionine modified electrode exhibits two-new redox couples.Two protons were involved in the electrochemical process undergone by the couple I in the pH range of 5.0-10.0. The apparent surface electron transfer rate constant is about 0.050s-1.

Studies on the Electrochemistry of Dopamine at a Pyrocatechol Sulfonephthalein Modified Glassy Carbon Electrode

The electrochemical response of dopamine(DA) at a pyrocatechol sulfonephthalein modified glassy carbon(PS/GC) electrode is reported. The electrode can be used as a detector for the determination of dopamine with a high stability and a good sensitivity. The cyclic voltammetric results indicated that there was a couple of well-defined redox peaks for dopamine at the PS/GC electrode with E_(pa)= 220 mV, E_(pc)=95 mV and the formal potential E^(o')= 157. 5 mV(vs. SCE) at 100 mV/s in the buffer solution of pH 7. 0. The PS/GC electrode can also be used to separate the electrochemical responses of ascorbic acid and DA by 54 mV with the differential pulse voltammetry. Under the selected conditions, the oxidation peak currents are linear with DA concetration in the range of 5. 0 × 10^(-6) to 5. 0 × 10^(-4) mol/L, and the detection limit is 1. 0 ×10^(-6) mol/L at S/N=3. Normalized with concentration, the relative sensitivity of dopamine to ascorbic acid reaches ca. 30. 8: 1.

酚酸基纳米金修饰电极检测食品中的亚硝酸盐和亚硫酸盐

基于酚酸良好的还原性和无污染性建立酚酸基纳米金传感体系,以实现亚硝酸盐和亚硫酸盐的灵敏检测。采用不同酚酸还原氯金酸制备纳米金(Gold nanoparticles,AuNPs),通过紫外光谱和交流阻抗法获得还原效果最佳的酚酸为没食子酸(Gallic acid,GA)。利用电沉积法制备GA@AuNPs@Au电极,并由线性扫描伏安法(Linear scanning voltammetry,LSV)表征亚硝酸盐和亚硫酸盐的电化学行为。优化体系条件为:GA浓度1 mmol/L、孵育温度70℃、反应时间60 min、pH6.0磷酸盐缓冲溶液浓度0.15 mol/L。亚硝酸盐和亚硫酸盐浓度在0.001~7 mmol/L范围内与氧化峰电流分别呈良好的线性关系(R2>0.994),检出限分别为0.20μmol/L和0.24μmol/L(S/N=3)。该修饰电极的重现性和稳定性良好,可用于实际样品中亚硝酸盐和亚硫酸盐的同时测定。

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.

Fabrication of CeO2 Nanoparticle Modified Glassy Carbon Electrode for Ultrasensitive Determination of Trace Amounts of Uric Acid in Urine

The preparation of a glassy carbon electrode modified by CeO2 nanoparticles was described, which was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. In pH 6.0 buffer, the CeO2 nanoparticle modified electrode （CeO2 NP/GC） gave an excellent electrocatalytic activity for the oxidation of uric acid （UA）. The catalytic current of UA versus its concentration had a good linear relation in the range of 2.0 × 10^-7-5.0 × 10^- 4 mol/L, with the correlation coefficient of 0.9986 and detection limit of 1.0 ×10^-7 mol/L. The modified electrode can be used for the determination of UA in urine, which can tolerate the interference of ascorbic acid up to 1000-fold. The method was simple, quick and sensitive.

Electrochemical response of MoS_(2) nanosheets/SiO_(2)-NH_(2) nanoparticles modified glassy carbon electrode to phenylacetic acid

Phenylacetic acid(PAA)is a primary raw material for illegal Methamphetamine(MATM)synthesis under the strong precursor chemicals supervisions of safrole and isosafrole.Therefore,trace detection of PAA at ultra-low concentration is a strategic technique and an urgent issue in the field of drug control.In this paper,trace determination of PAA at sub-nmol-L-1 concentration level is achieved by hydrogen bond adsorption and electrochemical catalysis through the prepared aminated SiO_(2)nanoparticles(SiO_(2)-NH_(2) NPs)and MoS_(2) nanosheets(NSs)modified glassy carbon electrode(GCE).The prepared MoS_(2) NS s/SiO_(2)-NH_(2) NPs modified electrode represents a detecting limit of 0.0989 nmol·L^(-1)and an obvious increasing linear range before the concentration increasement up to 60 nmol·L^(-1)in square wave voltammetry(SWV)responses of PAA.The SWV response of the modified electrode to PAA in the concentration range within 100 nmol·L^(-1)is higher than phenol,acetic acid(HOAc)and benzoic Acid(BEN).This electrochemical method for trace detection of PAA in aqueous solution with desired performance provides a feasible scheme for the detection of other drugs and aromatic precursor chemicals.

A novel ZnO/reduced graphene oxide and Prussian blue modified carbon paste electrode for the sensitive determination of Rutin

A carbon paste modified sensor based on a novel composite of zinc oxide nanoparticles deposited on reduced graphene oxide(ZnO-rGrO) and Prussian blue(PB) was drop-cast(ZnO-rGrO-PB/MCPE) for the sensitive estimation of Rutin(Rtn) at pH 7.0.The high surface area of ZnO-rGrO and electrocatalytic property of PB promotes the oxidation of Rtn. Field emission scanning electron microscope(FE-SEM) and energy-dispersive X-ray spectroscopy(EDX) techniques were employed to confirm the deposition of ZnO-rGrO and PB on carbon paste electrode(CPE). The ability of ZnO-rGrO-PB/MCPE in charge transfer at the interface was investigated using electrochemical impedance spectroscopy(EIS). The heterogeneous rate constant(ks) and the charge transfer coefficient(α) have been calculated as 6.08 s^(-1) and 0.74 respectively. This sensor showed a wide linear response for Rtn from 7.0×10^(-8)to 7.0×10^(-6) M and 7.0×10^(-6) to 1.0×10^(-4) M with a limit of detection(2.05±0.04)×10^(-8) M(S/N=3). The application of ZnO-rGrO-PB/MCPE was found in the analysis of Rtn in fruit juice samples using standard addition method. This sensor showed good reproducibility, stability, selectivity and sensitivity.

Square wave voltammetric quantification of folic acid,uric acid and ascorbic acid in biological matrix

Nowadays, modified electrodes with metal nanoparticles have appeared as an alternative for the electroanalysis of various compounds. In this study, gold nanoparticles（GNPs） were chosen as interesting metal nanoparticles for modifying carbon paste electrode（CPE）. GNPs and the gold nanoparticles-modified carbon paste electrode（GNPs/CPE） were characterized by UV–Vis spectroscopy, transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. GNPs/CPE as a simple and sensitive electrode was used to study three important biological molecules： folic acid（FA）, uric acid（UA） and ascorbic acid（AA）. Square wave voltammetry（SWV） was used as an accurate technique for quantitative measurements. A good linear relation was observed between anodic peak current（ipa） and FA（5.2 × 10（-6）– 2.5 × 10（-5）M）, UA（1.2 × 10（-6）– 2.1 × 10（-5）M） and AA（1.2 × 10（-6）– 2.5 × 10（-5）M） concentrations in simultaneous determination of these molecules.

Potentiometric Measurement of State-of-Charge of Lead-Acid Batteries Using Polymeric Ferrocene and Quinones Derivatives

Measurement of state-of-charge of lead-acid batteries using potentiometric sensors would be convenient;however, most of the electrochemical couples are either soluble or are unstable in the battery electrolyte. This paper describes the results of an investigation of poly (divinylferrocene) (PDVF) and Poly(diethynylanthraquinone) (PAQ) couples in sulfuric acid with the view to developing a potentiometric sensor for lead-acid batteries. These compounds were both found to be quite stable and undergo reversible reduction/oxidation in sulfuric acid media. Their redox potential difference varied linearly with sulfuric acid concentration in the range of 1 M - 5 M (i.e. simulated lead-acid electrolyte during battery charge/discharge cycles). A sensor based on these compounds has been investigated.

基于纳米银/聚L-谷氨酸修饰玻碳电极的电化学传感器用于泡菜中亚硝酸钠含量的测定

采用电沉积和电聚合的方式,将纳米银和L-谷氨酸修饰在玻碳电极上,制得纳米银/聚L-谷氨酸修饰玻碳电极(Poly-L-Glu/Nano-Ag/GCE)。以0.2 mol·L^(-1)磷酸盐缓冲溶液(pH 7.0)为支持电解质,以Poly-L-Glu/Nano-Ag/GCE为工作电极,饱和甘汞电极为参比电极,铂电极为辅助电极,在最佳检测条件下,采用循环伏安法进行测定。结果表明:Poly-L-Glu/Nano-Ag/GCE对亚硝酸钠具有较好的选择性,亚硝酸钠的浓度在4.14×10^(-6)~1.35×10^(-3) mol·L^(-1)内与对应的氧化峰电流的绝对值呈线性关系,检出限(3s/k)为4.14×10^(-7) mol·L^(-1),并且该电极的制备方法具有较好的重复性。将PolyL-Glu/Nano-Ag/GCE用于泡菜样品中亚硝酸钠的测定,检出量为1.33×10^(-5) mol·L^(-1),加标回收率为98.9%~103%。

介孔片层Ni_(2)FeS_(4)纳米结构修饰电极对尿酸的电催化研究

以硝酸镍、硝酸铁为金属源,硫代乙酰胺为硫源,以聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物(P123)为导向剂,与致孔剂的在不同金属比下用软模板法合成了介孔Ni_(2)FeS_(4)纳米片,在玻碳电极(GCE)上成膜构成尿酸传感器,通过循环伏安法(CV)、电流时间法(I-t)和差分脉冲伏安法(DPV)检测了修饰电极对尿酸的电催化性能,并将其应用于血清中的尿酸检测。探究了Ni_(2)FeS_(4)支持电解液的pH值及扫描速率的与峰电流的关系,研究结果表明,在最优条件下合成并修饰的电极对尿酸有较高的电化学活性、良好的选择性、稳定性和重现性,其线性范围和检出限分别为3~300和0.55μmol/L,用此方法对血清中的目标物进行测定,回收率为95.2%~103.8%。