Electrochemical detection of blood lead based on the enhancement effect of copper

The anodic stripping peak current of lead on the glassy carbon electrode surface was greatly increased in the presence of high concentration of copper ion. The effects of supporting electrolyte, concentration of Cu²⁺, accumulation potential and accumulation time were studied on the stripping peak current of Pb²⁺. As a result, a sensitive, simple and rapid electrochemical method was developed for the detection of lead. In 0.01 M HNO₃ solution containing 800 g,g L^?1 Cu²⁺, the stripping peak current of Pb²⁺ increases linearly with its concentration over the range from 2 to 100 μg L^?1. The detection limit is 1 μg L^?1 after 4-min accumulation at ?0.8 V. It was used to detect the concentration of lead in blood samples, and the results consisted with the values that obtained by atomic absorption spectrometry.     

Solid state spectroelectrochemistry of microparticles of ruthenium diimine complexes immobilised on optically transparent electrodes

The solid state electrochemistry and solid state spectroelectrochemistry of two ruthenium complexes, ruthenium tris-(4,7-diphenyl-1,10-phenanthroline) bis-hexafluorophosphate, [Ru(dpp)₃](PF₆)₂, and ruthenium bis-(2,2′-bipyridine)(4,6-diphenyl-2,2′-bipyridine)bis-hexafluorophosphate, [Ru(bpy)₂(dpb)](PF₆)₂, is described. Microparticles of the material are immobilised on ITO electrodes, and stable voltammetric signals are obtained in contact with aqueous electrolyte solution. Spectral changes monitored during a slow cyclic voltammetric scan confirm the exhaustive oxidation of the Ru²⁺ species to the Ru³⁺ form. The derivative of the absorbance signal monitored at a single wavelength during potential cycling is morphologically identical to a cyclic voltammogram with no background current. This technique is shown to be useful when peaks of small magnitude are obscured by capacitive background or when peaks close to the solvent limit are obscured by solvent electrolysis current. The technique effectively widens the electrochemical window available for voltammetric measurements. After suitable correction of the signal, the value of the voltammetric peak height (I _p) as well as peak potential (E _p) may be obtained from the derivative absorbance signal. Chronospectrometry is demonstrated to provide the equivalent to a chronocoulometric response, but is closer to the ideal simulated response. A facile method for simulating time or potential-dependant spectroelectrochemical responses using commercial electrochemical simulation software is described. Absorbance transients monitored during the electrolysis of solid particles of [Ru(dpp)₃](PF₆)₂ show best agreement with simulated data at very short and very long timescales. This observation, in conjunction with the observations from the potential scan experiments, suggests that the absorbance, charge, or current vs. time behaviour of the system can be adequately described by a semi-infinite diffusional model at short experimental timescales and by a finite diffusional model at sufficiently long timescales. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Dedicated to the 80th birthday of Keith B. Oldham.     

木犀草素在离子液体修饰电极上的电催化氧化及其测定

用1-丁基-3-甲基咪唑六氟磷酸盐([BMIM]PF₆)疏水性离子液体修饰玻碳电极,在0.2 mol/L磷酸盐缓冲溶液(pH为4.0～8.0)中,运用循环伏安法（CV）和差示脉冲溶出伏安法(DPSV)研究了木犀草素在修饰电极上的电化学行为,建立了测定木犀草素含量的新方法。 实验结果表明,该修饰电极上木犀草素氧化、还原峰电位均负移,峰电流增大。 在-0.2～0.7 V电位区间,pH=7.0的磷酸盐缓冲溶液体系中,木犀草素在修饰电极表面发生的是受吸附控制的准可逆等电子等质子电极反应,电子转移系数α=0.5,吸附量为4.6×10-10 mol/cm²;木犀草素氧化峰电流与其浓度在1.0×10^-10～1.6×10^-8 mol/L范围内呈良好的线性关系,检出限达到3.2×10^-11 mol/L,回收率为98.7%～102.0%;该法操作简单、快速、灵敏、准确;可用于野菊花中类黄酮的测定。     

Electrocatalytic Determination of Nitrite on a Rigid Disk Electrode Having Cobalt Phthalocyanine Prepared In Situ

This work reports an in situ cobalt(II) phthalocyanine (CoPc) synthesis on a SiO₂/SnO₂ (SiSn) matrix surface obtained by the sol‐gel method and its electrocatalytic activity for oxidation of nitrite. A rigid disk electrode with SiSn/CoPc was used to study the electrooxidation of nitrite by the cyclic voltammetric, chronoamperometric techniques and differential pulse voltammetry (DPV). The adsorbed phthalocyanine electrocatalyzed nitrite oxidation at 0.73 V (versus SCE) using the DPV technique. The anodic peak current intensities, plotted from differential pulse voltammograms in 1 mol L^?1 KCl for the concentration range 0.002 to 3.85 mmol L^?1 of nitrite were linear, with a correlation coefficient of 0.998 and a detection limit of 0.95 μmol L^?1.     

New adsorptive square wave method for trace determination of prilocain in the flow injection system by a fast fourier analysis

The determination of prilocain, used to manage tonic-clonic seizures, has been carried out at micro gold electrode (Au UME) using continuous fast Fourier transform square wave voltammetry. The Au UME electrode exhibited an effective response towards prilocaine adsorption. The peak current was also found to be significantly increased. The determination was carried out in phosphate containing electrolyte in the pH of 2.0 and a well-defined change on the peak current were noticed. The peak current was found to be linearly dependent on concentration of prilocain in the concentration range 5.0 × 10⁻⁷–1.0 × 10⁻¹¹ M with a detection limit of 5.0 × 10⁻¹² M. This paper describes development of a new analysis system to determine of prilocain by a novel square wave voltammetry method to perform a very sensitive method. The method used for determination of prilocain by measuring the changes in admittance voltammogram of a gold ultramicroelectrode (in 0.05 M H₃PO₄ solution) caused by adsorption of the prilocain on the electrode surface. Variation of admittance in the detection process is created by inhibition of oxidation reaction of the electrode surface, by adsorbed of prilocain. Furthermore, signal-to-noise ratio has significantly increased by application of discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as SW frequency, eluent pH, and accumulation time were optimized. The relative standard deviation at concentration 5.0 × 10⁻⁸ M is 5.8% for 5 reported measurements.     

Amperometric detection of hydrazine by cyclic voltammetry and flow injection analysis using ruthenium modified glassy carbon electrodes

Glassy carbon electrodes modified with (5-amino-1,10-phenanthroline)bis(bipyridine)ruthium(II) chloride hydrate, [(bpy)₂Ru(5-phenNH₂)]Cl₂·H₂O, are shown to oxidize hydrazine with excellent sensitivity. The presence of an amine group on the ruthenium complex facilitates electropolymerization onto the electrode surface. Using cyclic voltammetry, a large catalytic current is observed upon oxidation of hydrazine in phosphate buffer (pH 5.0), compared to the current obtained from the ruthenium-modified electrode with no hydrazine present. The sensitivity of cyclic voltammetry is sufficient for obtaining a linear calibration curve for hydrazine over the range of 10⁻⁵ to 10⁻² M. Hydrodynamic amperometry was used to determine the working potential for flow injection analysis. The limit of detection for hydrazine was determined to be 8.5 μM using FIA. The thickness of these films was shown to increase linearly with the number of electropolymerization cycles, in the range of 1000-2500 nm for 5-20 cycles, respectively, using Rutherford backscattering spectrometry (RBS). RBS analysis also suggests that the film is multilayered with the outermost layers containing a high ruthenium concentration, followed by layers where the concentration of ruthenium decreases linearly and approaches zero at the electrode surface.     

Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate

A newly modified electrode was prepared by mechanical immobilization of copper hexacyanoferrate (CuHCF) on a graphite electrode. The modified electrode was characterized by cyclic voltammetric experiments. The effect of different background electrolytes, pHs and scan rates on the electrochemical behaviour of the electrode has been evaluated. In NH₄Cl two reversible redox peaks were observed. The first redox peak corresponding to Cu⁺/Cu²⁺ is observed only in this medium. The second redox peak corresponds to the Fe(CN)₆ ^4–/Fe(CN)₆ ^3– couple. Both anodic peaks were used for catalytic oxidation of ascorbic acid. As the anodic current for catalytic oxidation was proportional to the amount of ascorbic acid, an analytical method was developed for the determination of ascorbic acid in commercial samples.     

Modifiying glassy carbon electrode with ferrocene-bridged polysilsesquioxanes

Ferrocene-bridged polysilsesquioxanes film electrodes were prepared via depositing the sols formed by hydrolysis of 1,1′-bis[(2-triethoxylsilyl)ethyl]ferrocene (BTEF) or co-hydrolysis of poly(vinylalcohol) (PVA) with BTEF or tetraethoxysilane (TEOS) with BTEF onto glassy carbon electrode (GCE) surface. The electrochemical behavior of the modified electrodes were characterized by cyclic voltammogram (CV) in aqueous solution. The BTEF film, BTEF/PVA film and BTEF/TEOS film all exhibit a redox wave at E^0’ are 0.504, 0.326, 0.318 V, with the peak potential separation (ΔE) are 0.132, 0.042, 0.028 V, and the value of i_pa/i_pc are 1.8097, 1.007, 1.064 (vs. SCE), respectively. This suggests that BTEF/PVA film and BTEF/TEOS film have a good reversible redox behavior and the redox peak is corresponded to a one-electron reduction and oxidation process. After successive 50 time’s cyclic voltammetric, there is no peak potential shift, and the peak current only decreased 5.58, 4.95%, respectively. BTEF/PVA film has better hydrophilicity and shows a more perfect electrocatalytic activity in the oxidation of H₂A than that of the BTEF/TEOS film. The catalytic peak current has a linear relationship with the concentration of H₂A in the range of 1.0 × 10⁻⁵~1.0 × 10⁻³ M.     

A Study of Preparation and Performance of a Dichlorvos Electrochemical Sensor Based on Molecularly Imprinted Technique

A new dichlorvos molecularly imprinted electrochemical sensor was prepared. The sensitive membrane sensor was fabricated by electro-polymerizing on an Au electrode surface using o-aminophenol as a monomer and dichlorvos as a template. The 5 mmol/L K₃[Fe(CN)₆] containing 0.1 mol/L KCl was used as the test background solution, while cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the properties of the senor. The changes of oxidation peak current versus dichlorvos concentration showed linearity in the range of 0.12–0.42 µmol/L (R ² = 0.9432) and 0.45–15 µmol/L (R ² = 0.9516) with a detection limit of 0.06 µmol/L (S/N = 3). Moreover, the selectivity and repeatability properties of the dichlorvos electrochemical sensor were examined. Results showed that the senor had excellent repeatability (RSD = 3.92%, n = 5), good selectivity to the dichlorvos in detection, and only a ten minute response time. Organophosphorus insecticides have some response signals in the detections.     

Nanoporous Pt Catalyst Modified by Sn Electrodeposition for Electrochemical Oxidation of Formaldehyde

A nanoporous Pt particles‐modified Ti (nanoPt/Ti) electrode was prepared through a simple hydrothermal method using aqueous H₂PtCl₆ as a precursor and formaldehyde as a reduction agent. The nanoPt/Ti electrode was then modified with limited amounts of tin particles generated by cyclic potential scans in the range of ?0.20 to 0.50 V in a 0.01 mol·L^?1 SnCl₂ solution, to synthesize a Sn‐modified nanoporous Pt catalyst (Sn/nanoPt/Ti). Electroactivity of the nanoPt/Ti and Sn/nanoPt/Ti electrodes towards formaldehyde oxidation in a 0.5 mol·L^?1 H₂SO₄ solution was evaluated by cyclic voltammetry and chronoamperometry. Electrooxidation of formaldehyde on the nanoPt/Ti electrode takes place at a potential of 0.45 V and then presents high anodic current densities due to the large real surface area of the nanoPt/Ti electrode. The formaldehyde oxidation rate is dramatically increased on the Sn/nanoPt/Ti electrode at the most negative potentials, where anodic formaldehyde oxidation is completely suppressed on the nanoPt/Ti electrode. Chronoamperogramms (CA) of the Sn/nanoPt/Ti electrode display stable and large quasi‐steady state current densities at more negative potential steps. Amperometric data obtained at a potential step of 100 mV show a linear dependence of the current density for formaldehyde oxidation upon formaldehyde concentration in the range of 0.003 to 0.1 mol·L^?1 with a sensitivity of 59.29 mA·cm^?2 (mol·L^?1)^?1. A detection limit of 0.506 mmol·L^?1 formaldehyde was found. The superior electroactivity of the Sn/nanoPt/Ti electrode for formaldehyde oxidation can be illustrated by a so‐called bifunctional mechanism which is involved in the oxidation of poisoning adsorbed CO species via the surface reaction with OH adsorbed on neighboring Sn sites.     

刺状Pd纳米粒子的室温合成及其对乙醇氧化的电催化性能

室温下以氯化胆碱为稳定剂,用化学还原法合成了刺状Pd纳米粒子(Pdtnh0o0r0n).透射电子显微镜和电化学循环伏安研究结果表明Pdtnh0o0r0n具有较高密度的台阶位,与商业Pd黑催化剂相比较,Pdtnh0o0r0n对乙醇氧化的电催化活性显著提高,氧化电流密度是商业Pd黑催化剂的1.2倍(-0.40--0.30V)-1.5倍(-0.65--0.40V),起始氧化电位和峰电位均负移50mV.相同电流密度下,Pdtnh0o0r0n催化剂对乙醇的氧化电位均更低.     

Voltammetric determination of sorbite at a mechanically renewed copper electrode

Potentials and currents of D-sorbitol oxidation peaks as a function of polarization conditions for a copper electrode in situ renewed by mechanically cutting a 0.5-μm surface layer are studied by direct-current cyclic voltammetry. Oxidation peaks of sorbite emerge in cyclic voltammograms recorded in alkaline supporting electrolytes (0.05–0.10 M KOH and NaOH solutions) upon scanning the potential to the anodic region (E _p = 0.50–0.58 V) and in the reverse direction (E _p = 0.60–0.62 V). The shape and parameters of these peaks depend on the concentration of KOH, because of the different copper oxides involved in the oxidation of sorbite formed at the electrode surface. The regeneration of the electrode surface is the necessary condition for good reproducibility of the peak parameters. The signals obtained on the surface of the unrenewed electrodes are almost halved and less reproducible. The calibration graph of the current of the sorbite oxidation peak as a function of its concentration is linear in the range from 5 × 10⁻⁴ to 1 × 10⁻² M.     

The phase transfer mechanism of 18-molybdophosphate anion at the water/nitrobenzene interface

The phase transfer mechanism of 18-molybdophosphate anion at the water/nitrobenzene interface has been investigated by chronopotentiometry with cyclic linear current-scanning (CLC) and cyclic voltammetry (CV). The transfer species is 18-molybdophosphtae anion with a charge number of 4, H₂[P₂Mo₁₈O₆₂]^4-. The transfer process is controlled by diffusion at a slow polarization rate and considerably influenced by pH of the aqueous phase. The stable forms and pH range of the heteropoly anion in the aqueous solution can be directly confirmed through voltammetric behavior. The theoretical analysis of the relationship between the transfer potential and solution pH is identical to the experimental results. The linear concentration relationship with the transfer peak current is suggested to be used in the determination of heteropoly acids (salts).     

Direct Electron Transfer of Horseradish Peroxidase in Gellan Gum–Hydrophilic Ionic Liquid Gel Film

A new composite film of microbial exocellular polysaccharide‐gellan gum (GG) and hydrophilic room temperature ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate (BMIMBF₄) was firstly used as an immobilization matrix to entrap horseradish peroxidase (HRP), and its properties were studied by UV/vis spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that BMIMBF₄ could promote the electron transfer between HRP and electrode surface, and the existence of GG could successfully immobilize BMIMBF₄ on the electrode surface with improved stability. HRP–BMIMBF₄–GG/GCE exhibited a pair of well‐defined and quasireversible cyclic voltammetric peaks in 0.1 M pH 7.0 phosphate buffer solutions at 1.8 V/s, which was the characteristic of HRP Fe(III)/Fe(II) redox couples. The formal potentials (E°′) was ?0.368 V (vs. SCE) and the peak‐to‐peak potential separation (ΔE_P) was 0.058 V. The peak currents were five times as large as those of HRP–GG/GCE. The average surface coverage (Γ*) and the apparent Michaelis‐Menten constant (K_m) were 4.5×10^?9 mol/cm² and 0.67 μM, respectively. The electron transfer rate constant was estimated to be 15.8 s^?1. The proposed electrode showed excellent electrocatalytic activity towards hydrogen peroxide (H₂O₂). The linear dynamic range for the detection of H₂O₂ was 0.05–0.5 μM with a correlation coefficient of 0.9945 and the detection limit was estimated at about 0.02 μM (S/N=3). BMIMBF₄–GG composite film was promising to immobilize other redox enzymes or proteins and attain their direct electrochemistry.     

Amperometric detection of dopamine based on tyrosinase-SWNTs-Ppy composite electrode

A novel 3-dimensional single wall carbon nanotubes (SWNTs)-polypyrrole (Ppy) composite was prepared as an electrode by chemically polymerizing polypyrrole onto SWNTs using a LiClO₄ oxidant. This composite electrode was characterized by scanning electron microscopy (SEM) and cyclic voltammetry with 1 mM [Fe(CN)₆]⁻³/[Fe(CN)₆]⁻⁴. The SWNTs were thickly coated with chemically polymerized polypyrrole and the composite had many surface pores and crevices which could enhance mass transfer. The SWNTs-Ppy composite electrode showed a large specific surface area (30 m²/g) and a good reproducible current response, at about 100 times the peak current of a glassy carbon electrode (GCE). The diffusion coefficient was calculated to be 4.81 × 10⁻⁶ cm²/s. As a biosensor application, tyrosinase was immobilized on the functionalized SWNTs and tyrosinase-SWNTs-Ppy composite was prepared in the same manner. This tyrosinase-SWNT-Ppy composite electrode was used for amperometric detection of dopamine in the presence of ascorbic acid and showed high sensitivity (467 mA/M cm²) and lower detection limit (5 μM) compared to previous reports.     

Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate

A newly modified electrode was prepared by mechanical immobilization of copper hexacyanoferrate (CuHCF) on a graphite electrode. The modified electrode was characterized by cyclic voltammetric experiments. The effect of different background electrolytes, pHs and scan rates on the electrochemical behaviour of the electrode has been evaluated. In NH₄Cl two reversible redox peaks were observed. The first redox peak corresponding to Cu⁺/Cu²⁺ is observed only in this medium. The second redox peak corresponds to the Fe(CN)₆ ^4–/Fe(CN)₆ ^3– couple. Both anodic peaks were used for catalytic oxidation of ascorbic acid. As the anodic current for catalytic oxidation was proportional to the amount of ascorbic acid, an analytical method was developed for the determination of ascorbic acid in commercial samples. Received: 26 May 1998 / Revised: 15 March 1999 / Accepted: 20 March 1999     

Subspeciation of nickel disulfide by carbon paste electrode voltammetry catalyzed by Ni2+

In subspeciation of sulfidic nickel, carbon paste electrode voltammetry was developed for the specific determination of Ni₃S₂ or NiS, but NiS₂ was found to be unreactive. Ni²⁺ in pH 7.2 acetate solution was able to catalyze NiS₂ to undergo redox reactions. The cyclic voltammogram showed two anodic peaks at –0.3 and +0.7 V and a cathodic peak at –0.6 V. The first anodic peak at –0.3 V and the cathodic peak were common among the three nickel sulfides, but the second anodic peak at +0.7 V was unique to NiS₂. This peak current gave a linear dose response to NiS₂ from 40 to 610 μg, with a correlation coefficient of 0.994, and a detection limit of 40 μg.     

Pitting corrosion of zinc in alkaline medium by thiocyanate ions

This paper describes the use of potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques in order to study the pitting corrosion susceptibility of a Zn electrode in KOH solutions containing KSCN as a pitting corrosion agent. Measurements were conducted under different experimental conditions. The results demonstrated that in the absence of KSCN, the anodic voltammetric response displays two anodic peaks prior to reaching the oxygen evolution potential. The first anodic peak A₁ is related to the electroformation of Zn(OH)₂. Peak A₁ is followed by a wide passive region which extends up to the appearance of the second anodic peak A₂. The latter is assigned to the formation of ZnO₂. Addition of SCN⁻ ions to the KOH solutions stimulates the anodic dissolution through peak A₁ and breaks down the passive layer prior to peak A₂. The breakdown potential decreases with an increase in SCN⁻ concentration and temperature, but increases with an increase in KOH concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases slightly with increasing applied positive potential, SCN⁻ concentration, and temperature.     

Electrochemical Determination of Vitamin B12 Based on Cu2+‐Involved Fenton‐like Reaction

Poly(thionine) (PTH) film was generated on the electrochemically activated glassy carbon electrode (GCE(ea)) by using the two‐step cyclic voltammetric scan. Scanning electron microscopy, infrared spectral analysis and electrochemical measurement were employed to characterize the modified electrode surface. Hydroxyl radicals, which were produced by the Fenton‐like reaction, could induce the effective oxidization of PTH under near‐neutral condition and cause the notable enhancement of the cathodic peak current (I_pc) during the potential cycling process. Due to the binding of copper ions with the ligands liberated from V_B12 and the inferior catalytic ability of Co²⁺ for the generation of hydroxyl radicals, the addition of V_B12 into the Cu²⁺?H₂O₂ system inhibited the oxidization of PTH and resulted in the decrease of the I_pc value. The cathodic peak current change was linear with the logarithm of the V_B12 concentration in the range of 10 nmol L^?1–100 μmol L^?1 with a detection limit of 2 nmol L^?1 under optimal conditions. The developed sensor displayed excellent analytical performance including high sensitivity, good selectivity, acceptable reproducibility and satisfactory stability. The V_B12 content in the injection sample was measured and the recovery values were in the range of 92.0 %–102 %.     

Very sensitive differential pulse adsorptive stripping voltammetric determination of 4-nitrophenol at poly (diphenylamine)/multi-walled carbon nanotube-β-cyclodextrin-modified glassy carbon electrode

In this work, a glassy carbon electrode (GCE) modified with poly (diphenylamine)/multi-walled carbon nanotubes-β-cyclodextrin (PDPA/MWCNT-β-CD) film was constructed and used for the determination of 4-nitrophenol (4-NP). Diphenylamine was successfully electropolymerised onto MWCNT-β-CD-modified GCE by cyclic voltammetry in monomer solution and 5 mol L^?1 H₂SO₄. The surface morphology of PDPA/MWCNT-β-CD film was characterised using scanning electron microscopy and electrochemical impedance spectroscopy. After adsorption of 4-NP on PDPA/MWCNT-β-CD at 0.2 V for 150 s, it showed a well-defined reduction peak in phosphate buffer solution at pH = 7. The PDPA/MWCNT-β-CD film enhanced the reduction peak current due to the complex formation between β-CD and 4-NP, presence of conductive polymer film as electron transfer mediator and also ability of MWCNTs for strong adsorptive and catalytic effect. Peak current increased linearly with 4-NP concentration in the range of 0.1 to 13.9 µg L^?1. The detection limit was obtained as 0.02 µg L^?1, which is better than other reported detection limits for the determination of 4-NP. The results showed that modified electrode has good sensitivity and selectivity. This sensor was used for the determination of 4-NP in water samples.