Metal Ion Uptake and Voltammetry on a Dithiocarbamate Containing Polymer Modified Electrode

Abstract

There is a need to expand the range of working electrodes which can be us in analytical voltammetry.

In this work, the synthesis of a thio containing (poly) N-Ethyl Tyramine electrode is described. Cyclic voltammetry, SEM and EPMA were used to characterise the modified electrode.

The ability of this electrode to uptake copper, nickel, mercury or cobalt ions from solution was investigated. Detection limits of the order of 0.1 ppm were estimated using differential pulse voltammetry.     

Electrochemical Behaviour and Square Wave Voltammetry of the Rice Herbicides Molinate,Bensulfuron-Methyl,Mefenacet and Thiobencarb

Abstract

Cyclic, differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of a group of herbicides used to treat rice crops: molinate, bensul-ruron-methyl, mefenacet and thiobencarb. The oxidation mechanism causes adsorption problems and consequent poisoning of the electrode surface by the products of the electrochemical reaction. Parameters such as pH, frequency and electrochemical electrode surface treatment were optimized. The analytical methodology developed using square wave voltammetry was applied to the determination of molinate and bensulfuron-methyl in simple or mixed commercial products.     

Direct Measurement of Traces of Vitamin C in Urine Using a Modified Glassy Carbon Electrode

Abstract

This report deals with the application of cyclic voltammetry for the preparation of polymer modified electrodes. The monomer used was diphenyl amine (DPA), and the electrolyte was HClO₄. Cyclic voltammetry was used because the polymer formed by this method adheres tightly to the electrode and also deposits as a very smooth layer. The polymer was then used on the glassy carbon electrode in order to make a modified electrode for detection of vitamin C in urine. Different variables were studied in order to find the most suitable conditions for this electrode. Linear response of electrode to ascorbic acid concentration was very high with limit of detection of 0.2 ppm.     

SrRuO3阳极催化剂的制备及对乙醇电催化氧化性能研究

用溶胶凝胶法制备了钙钛矿型氧化物SrRuO₃，热重分析和X射线衍射分别对制备过程和产物进行了分析和表征。采用循环伏安、计时电流和交流阻抗方法测试了所得产物对常温下碱性介质中乙醇电化学氧化的催化性能。循环伏安曲线、计时电流和交流阻抗结果表明：在乙醇溶液中，阳极电流密度明显大于氢氧化钾溶液中的阳极电流密度，并且随着电极中SrRuO₃含量的增加，电流密度也大幅度增加，在乙醇溶液中，SrRuO₃电极的电荷迁移阻抗明显降低。SrRuO₃对乙醇电化学氧化具有良好的催化作用。     

Use of Cyclic Voltammetry to Evaluate Sorption Properties of Cork Residues Towards Mn(II) in Waters

Cyclic voltammetry is proposed for evaluating the ability of cork wastes to remove Mn(II) ions by sorption from waters to be used for public supply. As the first stage, the concentration of several naturally occurring cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) were analyzed in the acid washings that were performed to remove them from the cork. The obtained results were then related to the total concentrations of cations released, as measured by flame atomic absorption spectroscopy of solutions made by dissolving ashed samples. Cyclic voltammetry is proposed to measure the manganese concentration in the uptake solutions because it allows the metal oxidation state to be controlled, and was determined to be suitable for use with standard addition methods. Contact time and particle size effects on Mn(II) sorption were evaluated.     

A Graphite‐Polyurethane Composite Electrode for the Analysis of Furosemide

A graphite‐polyurethane composite electrode has been used for the determination of furosemide, a antihypertensive drug, in pharmaceutical samples by anodic oxidation. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrooxidation process at +1.0 V vs. SCE over a wide pH range, with the result that no adsorption of analyte or products occurs, unlike at other carbon‐based electrode materials. Quantification was carried out using cyclic voltammetry, differential pulse voltammetry, and square‐wave voltammetry. Linear ranges were determined (up to 21 μmol L^?1 with cyclic voltammetry) as well as limits of detection (0.15 μmol L^?1 by differential pulse voltammetry). Four different types of commercial samples were successfully analyzed. Recovery tests were performed which agreed with those obtained by spectrophotometric evaluation. The advantages of this electrode material for repetitive analyzes, due to the fact that no electrode surface renewal is needed owing to the lack of adsorption, are highlighted.     

Electrochemical Behavior and Determination of Nicardipine

Abstract

The voltammetric behavior and measurement of nicardipine at the glassy carbon, carbon paste and hanging mercury drop electrodes are discussed. Cyclic voltammetry is used to elucidate the redox mechanism. Nicardipine is shown to adsorb on carbon electrodes, with the surface species retaining its electroactive characteristics. The adsorptive accumulation serves as a preconcentration step which improves the voltammetric measurement with respect to selectivity and sensitivity. Coupling this with a medium-exchange step eliminates interferences due to solution-phase electroactive species and permits direct measurement in urine. The inherent sensitivity of differential pulse voltammetry at the mercury electrode permits convenient measurement at the submicromolar level, with detection limit of 2 × 10^?8M. Amperometric detection for a flow injection system is illustrated.     

Synthesis and applications of copillar[5]arene dithiols

Abstract

A novel copillar[4+1]arene incorporating alkylthiol substituents was synthesised in three steps and structurally characterised as the first example of a pillar[n]arene to incorporate two terminal thiols on the same aromatic ring. The macrocycle was attached to gold electrodes through a standard dipping technique. Cyclic voltammetry demonstrated selectivity for Li⁺ over other alkali metal cations. The copillar[4+1]arene was also used as a capping agent in the preparation of 3 nm gold nanoparticles.     

Adsorptive/Extractive Stripping Voltammetry of 1,2,3,4-Tetrahydrocarbazole

Abstract

Adsorptive/extractive accumulation of 1,2,3,4-tetrahydrocarbazole at a carbon paste electrode is used to improve the subsequent voltammetric measurement with respect to sensitivity and selectivity. By simply immersing the electrode in the 1,2,3,4-tetrahydrocarbazole solution for a given period of time, and then transferring it to a blank solution, high degree of selectivity is achieved. After 10 min preconcentration, a detection limit near 1.4×10^-8M 1,2,3,4-tetrahydrocarbazole is obtained. Cyclic voltammetry is used to aid understanding the nature of the accumulation process. Applicability to measurements of other indole alkaloids and to analysis of urine samples is illustrated.     

The Electrochemical Behavior of Acetaminophen on Multi‐Walled Carbon Nanotubes Modified Electrode and Its Analytical Application

Abstract

A multi‐walled carbon nanotubes modified glassy carbon electrode (MWNTs/GCE) was fabricated, and the electrochemical behaviors of acetaminophen (ACOP) were investigated on the MWNTs/GCE. The results showed that MWNTs exhibited excellent electrocatalytic effects on the reaction of ACOP by accelerating the electron transfer rate. Cyclic voltammetry (CV) was used to explore the electrochemical redox mechanism of ACOP on the MWNTs/GCE and differential pulse voltammetry (DPV) was taken to determine ACOP in samples, respectively. The results showed that the oxidative peak currents were linear with the concentration of ACOP in the range of 4.0×10^?7–1.5×10^?4 mol l^?1 with the detection limit 1.2×10^?7 mol l^?1. The MWNTs/GCE showed satisfactory stability, selectivity, and it can be used to quantify ACOP in effervescent dosage real samples.     

Synthesis and characterization of low-melting ferrocenyl salts: a study of thermal and photochemical redox reactions

Abstract

The syntheses of bis(trifluoromethane) sulfonimide N-(ferrocenylmethyl) N,N,N-trimethyl ammonium salt 1 and bis(trifluoromethane) sulfonimide N′,N-bis(ferrocenylmethyl) inmidazolium salt 2 are reported. The compounds show low melting points, 76° and 125?°C, respectively, and were characterized by spectroscopic techniques ¹H-NMR, mass spectrometry, FT-IR spectroscopy, cyclic voltammetry, and XRD crystallographic analysis. Cyclic voltammetry results demonstrate that both salts have a quasi-reversible electrochemical behavior, similar to the reversible one shown by ferrocene under the same conditions. In the case of 1, a coupled chemical reaction was detected at slow scan rates after the oxidation. Transient species in the redox processes were investigated using flash photolysis and pulse radiolysis. In both cases, transient spectra of the products were similar to transient spectra observed for ferrocene. The decay kinetics of the oxidized and reduced transients were examined and mechanistic information was obtained. The experimental results show the potential uses of the two complexes as catalytic materials for electrochemical applications.     

Gold nanoparticles-carbon nanotubes modified sensor for electrochemical determination of organophosphate pesticides

An electrochemical sensor was developed for the detection of organophosphate pesticides based on electrodeposition of gold nanoparticles on a multi-walled carbon nanotubes modified glassy carbon electrode. Cyclic voltammetry was employed in the process of electrodeposition. Field emission scanning electron microscope and X-ray diffraction techniques were used for characterization of the composite. Organophosphate pesticides (e.g. parathion) were determined using linear scan voltammetry. A highly linear response to parathion in the concentration range from 6.0?×?10^?5 to 5.0?×?10^?7 M was observed, with a detection limit of 1.0?×?10^?7 M estimated at a signal-to-noise ratio of 3. The method has been applied to the analysis of parathion in real samples.     

Electrochemical Oxidation of Derivatives of Dibenzodiazepin. Dibenzothiazepin and Dibenzoxazepin

Abstract

Clozapin exhibits two anodic waves at ≥ 1 M H₂SO₄, but at lower acidities only the first two-electron wave remains. Cyclic voltammetry shows an ECE mechanism. Reversibility decreases at ≥ 10^?4 M concentrations, due to formation of an adsorptiob film. In nonaqueous solvents two irreversible one-electron waves appear. Clothiapin and loxapin are more difficultly oxidized and can be measured in the presence of clozapin.     

Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spec-troscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers(SAMs).A carboxylic acid-terminated thiol,such as thioctic acid(1,2-dithiolane-3-pentanoic acid),was self-assembled on gold electrodes.Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63-as a probe.The surface pka of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 ±0.1 and 5.8±0.1,respectively.The method is compared with other methods of monolayer pKa measurement.     

Analytical Potentialities of Carbon Nanotube/Silicone Rubber Composite Electrodes: Determination of Propranolol

A new composite electrode based on multiwall carbon nanotubes (MWCNT) and silicone‐rubber (SR) was developed and applied to the determination of propranolol in pharmaceutical formulations. The effect of using MWCNT/graphite mixtures in different proportions was also investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization of different electrode compositions. Propranolol was determined using MWCNT/SR 70 % (m/m) electrodes with linear dynamic ranges up to 7.0 µmol L^?1 by differential pulse and up to 5.4 µmol L^?1 by square wave voltammetry, with LODs of 0.12 and 0.078 µmol L^?1, respectively. Analysis of commercial samples agreed with that obtained by the official spectrophotometric method. The electrode is mechanically robust and presented reproducible results and a long useful life.     

Flow Injection Analysis of Phenolic Compounds with Carbon Paste Electrodes Modified with Tyrosinase Purchased from Different Companies

Abstract

Tyrosinase-modified carbon paste electrodes were prepared using lyophilised powder of the enzyme purchased from different companies. The selectivity of these electrodes for nine phenolic compounds, including six substituted catechols, has been studied. The signals obtained for catechol were always higher than those found for other phenolic compounds. Cyclic voltammetry and flow injection measurements indicated that the response of the tyrosinase-modified carbon paste electrodes was limited by the rate of the enzymatic oxidation of catechols. Different approaches of paste electrode preparation have been studied and compared. Direct mixing of enzyme into the graphite powder doped with the osmium based mediator, resulted in the highest sensitivity for the studied substrates. However, substrate selectivity was found to be dependent on the source of enzyme used for electrode preparation.     

Cyclic voltammetry study of (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)-N-phenylethanamide

As a continuation of our ongoing project on electrochemical properties of push-pull 5-substituted 2-alkylidene-4-oxothiazolidines (1a) differing in substituent R at C5-position and electron withdrawing group (EWG), we nave investigated the electrochemical behaviour of (5-etoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)-N-phenylethanamide 1a (R: =CHCO₂Et; EWG: CONHPh), consisting as a (2E,5Z)/(2Z,5Z) mixture, by cyclic voltammetry in polar as well as non-polar solvent (0.1 M TBAHFP in DMSO and CHCl₃, respectively). Cyclic voltammetry at stationary electrode was employed to characterize the electron transfer steps. Based on electrochemical criteria and correlation with the DigiSim simulations, an ECE mechanism, involving two electrochemical steps and one isomerisation step, was suggested. The article is published in the original.     

Monosubstituted ferrocene liquid crystals containing click triazole with a wide nematic phase temperature range

New monosubstituted ferrocenomesogens of the 1,4-substituted-1,2,3-triazole series 3a-3d and the 5-halogen-1,4-substituted-1,2,3-triazole series 4a-4d were successfully synthesised through a facile and versatile synthetic route using click reactions with moderate yields, in different atmospheres, and catalysed by different amounts of CuX (X = Br, I). Two series of compounds exhibited a typical nematic liquid crystal texture, and the 5-halogen-1,4-substituted-1,2,3-triazole series 4 had a wider mesomorphic temperature range than the corresponding series 3 due to the effect of the halogen atom substituent on the triazole. These compounds showed similar absorption spectra, but the fluorescence emission spectra of 4 were obviously redshift relative to 3. Cyclic voltammetry investigations revealed that the redox-active ferrocenyl groups of 3 and 4 follow one-electron transfer processes.     

Electrochemical Reduction of Phosphaallenes: Electron Spin Resonance and Theoretical Studies

Abstract

In order to check to what extent allenic systems containing one or two phosphorus atoms are likely to accept an electron, solutions of ArP?C?Cφ₂ (Ar Phenyltributyl; φ benzene) and ArP?C?PAr have been electrochemically and chemically reduced. Cyclic voltammetry shows that ArP?C?Cφ₂ undergoes irreversible reduction at -2266mV in THF while an irreversible reduction takes place at - 1900 mV (THF) for ArP?C?PAr.     

Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film‐modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at ?50 mV vs. SCE by electrochemical oxidation using differential pulse voltammetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly‐copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83–9.90 μmol L^?1, with detection limit 12.2 nmol L^?1 (2.02 μg L^?1).