Determination of trace amount of antimony (Ⅲ) by adsorption voltammetry on carbon paste electrode

A sensitive method is described for the determination of trace antimony based on the antimony-bromopyrogallol red (BPR) adsorption at a carbon paste electrode (CPE). Three steps were involved in the overall analysis: preconcentration,reduction and stripping. Optimal conditions were found to be an electrode containing 25% paraffin oil and 75% high purity graphite powder as working electrode;a 0.10 mol/L HCl solution containing 40 μmol/L BPR as accumulation medium;a 0.20 mol/L HCl solution as reduction and stripping electrolyte;accumulation time,150 s;reduction potential and time,-0.50 V,60 s;scan range from -0.50 to 0.20 V. Interferences by other ions were studied as well. The detection limit was found to be 0.5 nmol/L for 150 s preconcentration. The linear range was from 1.0 nmol/L to 0.50 μmol/L. Application of the proposed method to the determination of antimony in water and human hair samples gave good results.

Trace Determination of Scandium Using Adsorption Voltammetry of Mix-Polynuclear Complex of Scandium-Calcium-Alizarin Red S at Carbon Paste Electrode

A novel method was described for the determination of ultra trace amount of scandium based on the cathodic adsorptive voltammetry of the mix-polynuclear complex of scandium-calcium-alizarin red S at a carbon paste electrode (CPE). The 2nd-order derivative linear scan voltammograms of the adsorbed complex were recorded by model JP-303 polarographic analyzer from 0.0 to -1.0 V (vs. SCE). The experimental conditions of the working procedure were optimized. The results show that the complex can be adsorbed on the surface of the CPE, yielding one peak at -0.61 V, corresponding to the reduction of the alizarin red S in the mix-polynuclear complex at the electrode. The detection limit of Sc^(3+) is 1.0×10^(-10) mol·L^(-1) for 3 min of accumulation time. The procedure was successfully applied to the determination of trace amount of scandium in the sample ores.

Trace Determination of Zirconium(Ⅳ) by Anodic Adsorptive Voltammetry at a Carbon Paste Electrode

A new sensitive adsorptive voltammetric method was described for the determination of zirconium at a carbon paste electrode (CPE) in the presence of alizarin complexone (ALC). Optimal analytical conditions are: 1.0?0-6 or 5.0?0-7 mol/L ALC, 0. 20 mol/L HAC-NaAc (pH 4.3), accumulation for 60 s at 0 V (vs. SCE), and linear scanning from 0 V to 1.0 V at 250 mV/s. The peak potential of the complex is at 0.81 V. By using a model JP-303 polarographic analyzer, 2.0?0-10 mol/L (S/N=3) zirconium can be detected with a 90 s accumulation, when the 2nd-order derivative linear sweep technique is used, and the linear range is 6.0?0-10-2.0?0-8 mol/L (5.0?0-7 mol/L ALC) and 2.0?0-8-2.0?0-7 mol/L (1.0?0-6 mol/L ALC), respectively. The developed method was applied to the determination of trace zirconium in the ore samples with satisfactory results.

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.

Determination of captopril in patient human urine using ferrocenemonocarboxylic acid modified carbon nanotubes paste electrode

In this work,we describe a new strategy for the electrochemical determination of captopril（CA） using ferrocenemonocarboxylic acid as a mediator and multiwall carbon nanotubes as sensors in aqueous solution at pH 7.0.The diffusion coefficient（D）,and the kinetic parameters such as electron transfer coefficient（α）.and heterogeneous rate constant（kh）,for CA were also determined using electrochemical approaches.Under the optimized conditions,the electrocatalytic oxidation peak current of captopril showed two linear dynamic ranges with a detection limit of 0.3×10^-6 mol L^-1 captopril.The linear calibration range was 0.8×10^（-6） to 65×10^-6 mol L^-1 using cyclic voltammetry.Finally,this modified electrode was also examined as a selective,simple and precise new electrochemical sensor for the determination of captopril in real samples such as drug and patient human urine.

Cyclam Modified Carbon Paste Electrode as a Potentiometric Sensor For Determination of Cobalt(Ⅱ) Ions

A new modified carbon paste electrode based on cyclam as a modifier was prepared for the determination of Co(Ⅱ) ions. The proposed electrode shows a Nernstian slope 28.4 mV per decade over a wide concentration range 5.0×10 -6_1.0×10 -1 mol/L of Co 2+ ions with detection limit 2.5×10 -6 mol/L. The sensor exhibits good selectivities for Co 2+ over a wide variety of other cations. It can be used as an indicator electrode in potentiometric titration of cobalt(Ⅱ) ions as well as in direct determination of cobalt(Ⅱ) ions in wastewater of acidic cobalt electroplating bath. The electrode shows Nernestian behavior in a solution of 25% ethanol.

Electrocatalytic Oxidation of H_2 O_ 2 at a Carbon Paste Electrode Modified with a Nickel (Ⅱ)-5,11,17,23-Tetra-Tert-Butyl-25,27-Bis(Diethylcarbamoylmethoxy)Calix[4] Arene Complex and Its Application

Electrochemical behavior of a carbon paste electrode (CPE) modified with nickel(II)\|5, 11, 17, 23\|tetra\|tert\|butyl\|25, 27\|bis(diethylcarbamoylmethoxy)calix\arene (Ni(Ⅱ)\|L) complex and its electrocatalytic activity towards the oxidation of hydrogen peroxide were investigated by cyclic voltammetric technique in a 5.0×10 -2 mol/L NaClO 4+ 1.0×10 -3 mol/L NaOH solution. It was found that Ni(II)\|L acts as an effective catalyst for the oxidation of hydrogen peroxide. The modified electrode exhibited a linear response over a hydrogen peroxide concentrations in the range of 2.0×10 -6 \|1.0×10 -4 mol/L with a detection limit as low as 1.0×10 -6 mol/L. The relative standard deviation was 3.5% for 5 successive determinations of H 2 O 2 at 1.0×10 -5 mol/L. The modified electrode was used successfully in rainwater analysis.

Electrocatalytic oxidation of hydrazine on magnetic bar carbon paste electrode modified with benzothiazole and iron oxide nanoparticles: Simultaneous determination of hydrazine and phenol

A magnetic bar carbon paste electrode （MBCPE） modified with Fe3O4 magnetic nanoparticles （Fe3O4NPs） and 2‐（3,4‐dihydroxyphenyl） benzothiazole （DPB） for the electrochemical determina‐tion of hydrazine was developed. The DPB was firstly self‐assembled on the Fe3O4NPs, and the re‐sulting Fe3O4NPs/DPB composite was then absorbed on the designed MBCPE. The MBCPE was used to attract the magnetic nanoparticles to the electrode surface. Owing to its high conductivity and large effective surface area, the novel electrode had a very large current response for the electrocat‐alytic oxidation of hydrazine. The modified electrode was characterized by voltammetry, scanning electron microscopy, electrochemical impedance spectroscopy, infrared spectroscopy, and UV‐visible spectroscopy. Voltammetric methods were used to study the electrochemical behaviour of hydrazine on MBCPE/Fe3O4NPs/DPB in phosphate buffer solution （pH = 7.0）. The MBCPE/Fe3O4NPs/DPB, acting as an electrochemical sensor, exhibited very high electrocatalytic activity for the oxidation of hydrazine. The presence of DPB was found to reduce the oxidation potential of hydrazine and increase the catalytic current. The dependence of the electrocatalytic current on the hydrazine concentration exhibited two linear ranges, 0.1–0.4 μmol/L and 0.7–12.0 μmol/L, with a detection limit of 18.0 nmol/L. Additionally, the simultaneous determination of hydrazine and phe‐nol was investigated using the MBCPE/Fe3O4NPs/DPB electrode. Voltammetric experiments showed a linear range of 100–470 μmol/L and a detection limit of 24.3 μmol/L for phenol, and the proposed electrode was applied to the determination of hydrazine and phenol in water samples.

Mixed Binder Carbon Paste Electrode for Quantitation of Isoniazid in Serum

This paper covers the construction and behaviour of a mixed binder carbon paste electrode system appropriate for the cathodic stripping voltammetric quantitation of iso-niazid. The mixed binder consisted of glycerol and liquid paraffin. At the mixed binder carbon paste electrodes in a pH 3.0 buffer solution, isoniazid showed two sensitive cathodic stripping voltammetric wave at-0. 75 V (p1) and-0. 88 V (p2) , respectively. The p2 can be used for the determination of trace amounts of isoniazid, the linear range of the peak current to the isoniazid concentration being from 5. 0×10-7 to 5.0×10-5 mol/L, and the limit of detection being 1. 0×10-7 mol/L with a relative standard deviation of 6. 0%(n=10). The proposed method was directly used to determine the drug in blood serum without the pretreatment of blood serum.

Carbon Paste Electrode Modified by Surfactant for Anodic Stripping Voltammetric Determination of Sulphadiazine

he present paper covers the construction and behaviour of a mixed binder car-bon paste electrode modified by surfactant system appropriate for the anodic strip-ping voltammetric quantitation of sulphadiazine. The mixed binder consisted ofglycerol and liquid paraffin. On this electrode in a PH 8. 20 buffer solution sulpha-diazine yields a sensitive anodic stripping voltammetric wave at 0. 82 V. It can beused for the determination of trace amounts of drug, the linear range of the peakcurrent to the sulphadiazine concentration being from 1. 0 x 10-7 to 5. 0 x 10-5mol/L, and the detection limit being 6. 6 x 10-9 mol/L with a relative standard de-viation of 2. 6% (n= 15).The proposed method was used to determine the drug inurine samples.

Gold Nanoparticle-based Layer-by-Layer Enhancement of DNA Hybridization Electrochemical Signal at Carbon Nanotube Modified Carbon Paste Electrode

Colloid gold nanoparticle-based layer-by-layer amplification approach was applied to enhance the electrochemical detection sensitivity of DNA hybridization at carbon nanotube modified carbon paste electrodes （CNTPEs）. Streptavidin was immobilized onto the surface of CNTPEs, and the conjugation of biotin labeled target oligonucle,otides to the above immobilized streptavidin was performed, followed by the hybridization of target oligonucleotides with the gold nanoparticle-labeled DNA probe and then the layer-by-layer enhanced connection of gold nanoparticles, on which oligonucleotides complementary to the DNA probe were attached, to the hybridization system. The differential pulse voltammetry （DPV） signal of total gold nanoparticles was monitored. It was found that the layer-by-layer colloidal gold DPV detection enhanced the sensitivity by about one order of magnitude compared with that of one-layer detection. One-base mismatched DNA and complementary DNA could be distinguished clearly.

Voltammetric Determination of Estrogens Based on the Enhancement Effect of Surfactant at Carbon Paste Electrode

Highly sensitive voltammetric method for the determination of estrogens, based on the enhancement effect of cetyltrimethylammonium bromide (CTAB) has been described. In the presence of CTAB, the oxidation peak currents of estrogens (estradiol, estrone, estriol, estradiol valerate and diethylstilbestrol) as the carbon paste electrode (CPE) increased significantly after open-circuit accumulation. The peak current was proportional to the concentration of estradiol over the range from 5×10?9 to 2.5×10?6 mol·L?1. The detection limit was 8×10?10 mol·L?1 at 6 min of accumulation. The total amounts of estrogens in the blood serums were determined and the average recovery was 104.92%. Under the conditions used, the electrode process of estradiol was examined the mechanism for peak current enhancement was also discussed.

SBA-15 Modified Carbon Paste Electrode for Rapid cTnI Detection with Enhanced Sensitivity

A novel electrochemical immunoassay for cardiac troponin Ⅰ （cTnI） combining the concepts of the dual monoclonal antibody ＂sandwich＂ principle, the silver enhancement on the nano-gold particle, and the SBA-15 mesoporous modified carbon paste electrode （SBA-MCPE） is described. Four main steps were carried out to obtain the analytical signal, i.e., electrode preparation, immunoreaction, silver enhancement, and anodic stripping voltammetric detection. A linear relationship between the anodic stripping peak current and concentration of cTnI from 0.5 to 5.0 ng/mL and a limit of detection of 0.2 ng/mL of cTnI were obtained.

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.

Adsorptive Stripping Voltammetry of Ultra Trace Lanthanum（Ⅲ） Using an Alizarin S as Complexing Agent and Carbon Paste as Working Electrode

Ultra trace determination of lantanum（Ⅲ） has been studied by adsorptive stripping voltammetry methods using an alizarin S as complexing agent and carbon paste electrode as working electrode. The electrode was made from mixed of carbon powder and paraffin in micropipette tip with diameter of 4 ram. This method consists of two steps. The first step is the formation and adsorptive accumulation of metal ion with chelator at the electrode surface. The second step is stripping the complex from the electrode surface into the solution. The stripping step generates current which is recorded as voltammogram. The optimum conditions of instrumental parameter obtained were accumulation potential of 600 mV, accumulation time of 120 seconds, and pH of solution of 5.5. In this research, the limit detection obtained was 2.3348 × 10^-12 M （3.24× 10^-11μg/L） with sensitivity of 16.52 （nA/10u M） and the precision of standard solution of La3＋ with concentration of 2 × 10^-12 M, 4× 10^-12 M, 6 × 10^-12 M, 8 × 10^-12 M, and 10 × 10^-12M were 3.50%, 9.88%, 7.19%, 7.48% and 1.85% respectively. The linierity of this method is very good with correlation coefficient is 0.9780. Recovery percentage from La3＋ with concentration of 6× 10^-12 M and 10 × 10^-12 M are 108.84% and 91.51%, respectively.

Carbon Paste Electrodes for the Analysis of Some Agricultural Pollutants and Trace Metals

The present work is concerned with the voltammetric application of unmodified tricresyl phosphate carbon paste electrode （TCP-CPE） and in situ bismuth-film modified tricresyl phosphate-based carbon paste electrode （BiF-TCP-CPE）. The TCP-CPE was examined with the main objective of using it for the differential pulse voltammetric analysis of some neonicotinoid insecticides in aqueous Britton-Robinson buffer solution pH 7.0 as supporting electrolyte. After comparing the performance of the TCP-CPE with that of silicone oil carbon paste electrode, quantitative analysis of imidacloprid, thiamethoxam and clothianidin was performed in model solutions and real samples （river water and commercial insecticide formulations）. The in situ prepared BiF-TCP-CPE was tested for a simultaneous detection of selected heavy metal ions （Cd^2＋ and Pb^2＋） at a μg/dm^3 concentration level, using square wave anodic stripping voltammetric technique. The influence of different electrochemical pretreatments of the working electrode on the bismuth deposition and analyte signals were investigated. Film formation was studied at untreated, pre-cathodized and pre-anodized TCP-CPEs in the acetic buffer solution pH 4.6, containing 1 μg/cm^3 Bi （III）.

The attachment of Staphylococcus epidermidis on the surface of a carbon paste electrode at various positive potentials:The effect of pH,incubation time,and solid-medium type

The attachment of Staphylococcus epidermidis to the surface of carbon paste electrode (CPE) by applying positive potentials (50 - 600 mV) with regard of various buffer pH, cultivation time and solid-medium type was studied. The attachment process was analyzed by measuring the electric current derived from the dye (amido black) adsorbed on the vacant areas of CPE after attachment of microbial cells. The pH was not identified as a single main factor affecting the attachment (p > 0.05), however further insight revealed that the potentials applied had different effects on the microbial cells attachment. Both cultivation time and solid-medium type significantly affected the microbial attachment. Generally, increase of cultivation time up to 168 h resulted in increase of adhesion. Applying potentials 300, 400 and 200 mV resulted in the highest attachment process for bacteria cultivated for 24, 48 and 168 h, respectively. S. epidermidis cultivated on the blood agar and Baird-Parker agar plates showed the higher extent of attachment.

Electrochemical behavior of insulin on pretreated carbon black electrode enhanced with silicon carbide nanostructure

We previously reported the direct electrochemical detection of insulin at bare carbon electrodes. Here a novel modified acetylene carbon black paste electrode(SiC/CB-CPE), based on the outstanding characteristics of silicon carbide nanostructure,was developed for the electrooxidation of insulin in alkaline solution and it was characterized by cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) in 5 mmol/L Fe(CN)63-/4- solution. It is found that silicon carbide nanostructure doped into the CB-CPE greatly facilitates the redox electrochemistry of Fe(CN)63-/4- probe and the electrochemical oxidation of insulin. The electrooxidation of insulin is a one-electron and one-proton reaction and an irreversible adsorption-controlled electrode process. The anodic oxidation current increases linearly with the concentration of insulin from 1×10-7mol/L to1.2×10-6mol/L in 0.1 mol/L Na2CO3-NaHCO3 buffer solution(pH 10.0) and the detection limit was 50 nmol/L. In addition, the SiC/CB-CPE shows good sensitivity, reproducibility, renewability and capacity of resisting disturbance.

Preparation, Electrochemical Property and Application in Bulk-modified Electrode of Dawson-type Phospho-molybdate-doped Polypyrrole Composite Nanoparticles

A kind of inorganic-organic hybrid semiconductor composite nanoparticles： Dawson-type phosphomolybdate- doped polypyrrole （P2Mo18-PPy） was designed and prepared using microemulsion oxidation-polymerization at room temperature and characterized by TEM and IR. The P2Mo18-PPy was used as a bulk-modifier to fabricate a chemically modified carbon paste electrode（CPE） by direct mixing, which represents the example of polyoxometalates（ POMs）- doped semiconductor polymer nanoparticles modified electrode. Both the advantage of POMs-doped polymer and the surface-renewal property of the CPE were fully utilized. The electrochemical behavior of the P2Mo18-PPY bulk-modified CPE（P2Mo18-PPy-CPE） was investigated with cyclic voltammetry. Three couples of reversible redox peaks were observed in the range from ＋ 800 to 0 mV, which corresponded to the reduction and oxidation through two-, four- and six-electron processes, respectively. The P2 Mo18-PPY-CPE showed a high electrocatalytic activity for the reduction of nitrite, which expanded the application of POMs-doped semiconductor polymer nanoparticles.

New Inorganic-organic Hybrid Compound Containing One Dimensional Keggin Polyoxometalate [SiW_(11)O_(39)Co]^(6-) Chains: Preparation, Characterization and Application in Chemically Bulk-modified Electrode

A new inorganic-organic hybrid compound based on polyoxometalate and organic ligand formulated as （H2bpp）3[SiWlIO39Co]-2H20（1）[bpp=l,3-bis（4-pyridyl）propane] was hydrothermally synthesized and structurally characterized by elemental analysis, single-crystal X-ray diffraction, IR, TG, and cyclic voltammetry. Single-crystal X-ray diffraction analysis reveals that compound 1 consists of interesting cobalt-monosubstituted POMs one dimensional chain together with protonated bpp ligands. Additionally, the polyoxoanions combined with the discrete organic substrates by hydrogen bond interactions to afford a supramolecular 3D network structure. The hybrid compound 1 was used as a bulk modifier to fabricate a three-dimensional chemically modified carbon paste electrode（1-CPE） by direct mixing. The electrochemical behavior and electrocatalysis of 1-CPE were studied in detail. The results indicate that 1-CPE has good electrocatalytic activities toward the reduction of nitrite or bromate in 1 mol/L 1-12SO4 aqueous solution. 1-CPE shows remarkable stability that can be ascribed to the insolubility of compound 1 and the supramolecular interactions existed between 1D POM anion chains and organic ligand bpp, which is very important for practical applications in electrode modification.