Preconcentration and determination of Bismuth (III) at a chemically modified electrode containing 1-(2-pyridylazo)-2-naphthol

A chemically modified electrode (CME) containing 1-(2-pyridylazo-2-naphthol is evaluated for its ability to preconcentrate bismuth(III) prior to quantification by voltammetry. The CME approach is shown to be sufficiently sensitive for sub-nanomolar concentrations to be determinable after chemical deposition for 60 sec. Further, when the bismuth is deposited from iodide-containing sulphuric acid media, the discrimination against interference by copper(II) is significantly better than that obtained with conventional stripping analysis. The results obtained for Bi(III)( in an NBS reference solution agree well with the recommended value.     

Indirect Determination of Trace Copper(II) by Adsorptive Stripping Voltammetry with Zincon at a Carbon Paste Electrode

Traces of copper(II) can be determined by adsorptive stripping voltammetry using 2‐carboxy‐2′‐hydroxy‐5′‐sulfoformazyl benzene (Zincon) as complex forming reagent. First in phosphate buffer pH 6.4, copper(II)‐Zincon complex was adsorbed on carbon paste electrode (CPE) with an accumulation potential of 0.6 V. Following this, adsorbed complex was oxidized and detected by differential pulse voltammetric (DPV) scan from 0.6 to 1.0 V. The effective parameters in sensor response were examined. The detection limit (DL) of copper(II) was 1.1 μg/L and relative standard deviations (RSDs) for 10 and 200 μg/L Cu(II) were 1.81 and 1.03%, respectively. The calibration curve was linear for 2–220 μg/L copper(II). The resulting CPE does not use mercury and therefore, has a positive environmental benefit. The method, which is reasonably sensitive and selective, has been successfully applied to the determination of trace amount of copper in water and human hair samples.     

Poly-salicylic acid modified glassy-carbon electrode and its application

A poly-salicylic acid modified glassy-carbon electrode (PSAMGCE) was prepared by electro-polymerisation. The behaviour of copper on this electrode was investigated by anodic stripping voltammetry. The electrode is about 40 times more sensitive than the unmodified glassy-carbon electrode. It was applied to the determination of trace copper(II) in water, and shows a 96-106% recovery and a relative standard deviation of ca. 3%.     

Stripping voltammetric determination of copper(II) in natural waters and human hairs based on the adsorption of its complex with Kryptofix 22 on the carbon paste electrode

Traces of copper(II) can be determined by adsorptive stripping voltammetry using Kryptofix 22 as complex forming reagent. First, copper(II)-Kryptofix 22 complex was adsorbed on the carbon paste electrode in phosphate buffer pH 5.3 with an accumulation potential of −0.5 V. Following this, the adsorbed complex was oxidized and detected by anodic differential pulse voltammetric scan from −0.2 to 0.1 V. The effective parameters of sensor response were examined. The detection limit of copper(II) was 1.1 μg/L and relative standard deviations for 50 and 150 μg/L of Cu(II) were 1.2 and 0.96%, respectively. The calibration curve was linear for 2–150 μg/L of copper(II). This technique does not use mercury and therefore is environmentally beneficial. The method, which is reasonably sensitive and selective, has been successfully applied to the determination of trace amounts of copper(II) in water and human hair samples.     

Catalytic reduction currents in the stripping voltammetry of solutions of the system copper(II)-ascorbic acid and their application in analytical chemistry

It has been found that the analytical signal from copper(II), cadmium(II), and zinc(II) in alternating-current stripping voltammetry in the presence of ascorbic acid (AA) increases only for copper(II) ions, which have significant oxidative potential. It is associated with the appearance of a catalytic current of the reducer in stripping voltammetry, where the reducer is AA. A scheme has been proposed for this process. The rate constant has been calculated for the chemical reduction of copper(I) ions, electrochemically produced in the diffusion layer as a result of the electrochemical oxidation of copper atoms, with AA. A procedure has been developed for the determination of copper in model solutions using the catalytic current of AA; the limit of copper detection is 0.01 μg/L, which is one order lower than the one achieved without AA.     

Adsorptive voltammetric determination of copper as its nioximate complex

A sensitive and selective stripping voltammetric ultratrace determination of copper is described, based on adsorptive accumulation of the cu(II)-nioxime complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The analytical conditions for the determination of copper by differential-pulse and linear-scan absorption voltammetry have been optimized. The method is compared to the routine anodic stripping voltammetric method for copper. Its applicability to river and potable water analysis is illustrated. The detection limit, restricted by the blank, is about 0.5 microg/l.; the relative standard deviation (at microg/l. level) for a standard solution is below 5% and for water samples is 5-9%.     

Linear scan stripping voltammetry of copper(II) at the chemically modified carbon paste electrode

A new chemically modified electrode (CME), -benzoinoxime (CUPRON) modified carbon paste electrode, for determining copper(II) is reported because of its excellent selectivity and sensitivity. The electrode is made by mixing a quantity of CUPRON (25%, w/w) with graphite powder (50%, w/w) and paraffin oil (25%, w/w). The CME preferentially deposits copper from the pH 8.5 NH₃-NH₄Cl buffer solution containing copper(II) under an open circuit and most of metal ions do not interfere with the measurements. The detection limit (S/N of three) for determining Cu(II) is 3 × 10^–10 g/ml after 10 min accumulation in fast linear scan stripping voltammetric measurement. Linear calibration curves are obtained for Cu(II) concentration ranged from 1 × 10^–8 M to 1 × 10^–6 M. The response can be maintained with relative standard deviation of 6.0% in a 5 × 10^–6 M Cu(II) solution after eight accumulation/measurement/ regeneration cycles at the same electrode surface. The effect resulted from carbon paste preparation, reduction potential, electrode renewal, electrolyte and solution pH, preconcentration time, concentration dependence, possible interference and other variables has been evaluated. As for application, the CME demonstrates its high sensitivity and copper-selectivity in complex composition samples, such as anodic mud and polluted water.     

Electro-inorganic synthesis: a convergent paired electrochemical synthesis and voltammetric studies of copper(II)-2-aminophenol derivatives

Electrochemical reduction of 2-nitrophenol and 5-methyl-2-nitrophenol has been studied in water/ethanol mixture using cyclic voltammetry and controlled-potential coulometry. Our voltammetric data indicate the formation of 2-aminophenol (HL^I) and 5-methyl-2-aminophenol (HL^II), respectively. Also, the electrochemical synthesis of copper(II) complex of 2-aminophenols has been carried out using copper metal as a sacrificial anode and lead metal as a cathode in water/ethanol (50/50 v/v). The electrochemical synthesis of copper(II)-2-aminophenols consists of a multi-step such as (a) cathodic reduction of 2-nitrophenols to related 2-aminophenols, (b) generation of Cu²⁺ from copper anode, (c) complexation of 2-aminophenols with Cu²⁺. In this work, we have proposed a mechanism for the electrode process. Some parameters such as electrode material, current density, electricity passed and temperature, were also systematically studied. The convergent paired electrochemical synthesis of copper(II) complex of 2-aminophenols has been successfully performed in a one-pot process, under constant current condition in an undivided cell, in a good yield and purity. Also, the electrochemical behavior of copper(II)-2-aminophenol complex was studied and the stability constant of copper(I)-2-aminophenol complex was evaluated using cyclic voltammetry.     

A Study of the Determination of Cu(II) by Anodic Stripping Voltammetry on a Novel Nylon/Carbon Fiber Electrode

In this work we report a new electrode material formed by injection‐moulding of a conducting polymer consisting of carbon fibers in a Nylon matrix. This material is highly conductive, inexpensive, easy to mould in different shapes and requires minimal pretreatment. The electrode was tested as a mercury‐free sensor for the trace determination of Cu(II) by anodic stripping voltammetry (ASV). The deposition and stripping behavior of copper on the conducting material was initially studied by cyclic voltammetry and the chemical and instrumental parameters of the determination were investigated. The electrode has been shown to be suitable for the determination of Cu(II) in the range 8 μg L^?1 to 30 mg L^?1 (with deposition times ranging from 30 s to 10 min) with a relative standard deviation of 2.2% (at the 0.5 mg L^?1 level) and a limit of detection of 8 μg L^?1 Cu(II) for 10 min of accumulation (at a S/N ratio of 5). The electrode was, finally, applied to the determination of copper in tap‐water, pharmaceutical tablets and bovine serum with recoveries of 97.4, 94.9 and 93.4%, respectively     

Theoretical Analysis and Determination of the Heterogeneous Stability Constant of Copper(II)-Humic Acids Complex at Chemically Modified Carbon Paste Electrode

A theory for determining the heterogeneous stability constant of a metal complex system at the surface of a chemically modified carbon paste electrode was developed. The proposed theory has been applied to the studies of a copper(II)-humic acids (Has) complex system. In an open circuit, copper(II) was accumulated from a stirred preconcentration medium onto the HAs-CMCPE. The subsequent electrochemical measurement was performed in a small volume of Britton-Robinson (B-R) buffer (pH 3.78). By means of cyclic voltammetry (CV) and anodic stripping voltammetry (ASV), the determined average heterogeneous stability constant of copper(II)-HAs complex was 4.99×10⁹.     

Determining Trace Concentrations of Copper in Water by Cathodic Film Stripping Voltammetry with Adsorptive Collection

Abstract

A technique is presented for the determination of trace concentrations of copper (II) in natural water samples by cathodic stripping voltammetry of a film of copper-catechol complex ions adsorbed on the hanging mercury drop electrode. The peak height of the copper-catechol reduction peak is linearly dependent upon the copper (II) concentration between 10^?10 and 10^?7 M. The detection limit of the technique is below 10^?10 M copper (II) for a collection time of 3 minutes, but the sensitivity can be further increased four-fold by collecting for 15 minutes. The sensitivity is reduced by high concentrations of competing trace metals and of surfactants, which necessitate the use of standard additions to the sample.     

Catalytic flow-injection determination of copper at nanogram levels by using color formation of N-phenyl-p-phenylenediamine with m-phenylenediamine in the presence of pyridine and ammonia as activators

A spectrophotometric flow-injection method for determining copper(II) has been developed. It is based on the catalytic effect of copper(II) on the oxidative coupling of N-phenyl-p-phenylenediamine with m-phenylenediamine in the presence of hydrogen peroxide. Pyridine and ammonia as activators increased the absorbance for the copper(II)-catalyzed coloration, and the dye formed was stabilized by adding a non-ionic surfactant. The working range of the method was 0.1-2.0 ng ml(-1) of cooper(II) with a relative standard deviation 2.4% at a sampling rate of 30 h(-1). Interference from iron(III) was effectively suppressed by citric acid. Copper in natural water samples can be determined easily.     

A Selective Film Based on Poly(3‐octylthiophene) Doped with Dihydroxyanthraquinone Sulfonate

A stable film of poly(3‐octylthiophene)–dihydroxyanthraquinone sulfonate has been synthesized electrochemically in non‐aqueous solution. The incorporation of dihydroxyanthraquinone sulfonate as an anionic complexing ligand into poly(3‐octylthiophene) film during electropolymerization was achieved and copper ions were accumulated by reduction on the electrode surface. The presence of dihydroxyanthraquinone sulfonate during the electrochemical polymerization of 3‐octylthiophene is shown to impact the sensitivity and the stability of the organic conducting film electrode response. The electroanalysis of copper(II) ions using conducting polymer electrode was achieved by differential pulse anodic stripping voltammetry with remarkable selectivity. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 50–400 ng mL^?1 copper(II) ion for 240 seconds accumulation time and the limit of detection was found to be 7.8 ng mL^?1. To check the selectivity of the proposed stripping voltammetric method for copper(II) ion, various metal ions as potential interferents were tested. The developed method was applied to copper(II) determination in certified reference material, NWRI‐TMDA‐61, trace elements in fortified water.     

A Robust Electrochemical Sensor Based on Butterfly-shaped Silver Nanostructure for Concurrent Quantification of Heavy Metals in Water Samples

Heavy metals in drinking water have become a severe threat to human health. Detection of heavy metals has been achieved by electrochemical sensors that are modified with complex nanocomposites; however, reproducibility of these sensors is still a big challenge when applied in commercial settings. Here, a simple, very robust, and sensitive electrochemical sensor based on a screen-printed carbon electrode modified with butterfly-shaped silver nanostructure (AgNS/SPCE) has been developed for the concurrent determination of cadmium (II), lead (II), copper (II), and mercury (II) in water samples. The electrochemical behavior of the modified electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. The AgNS/SPCE showed distinct peak potentials and a significant increase in the peak currents for all heavy metals, attributed to the high electrical conductivity and electrocatalytic activity of the synthesized butterfly-shaped AgNS. Moreover, the excellent stability and sensitivity towards simultaneous quantification of heavy metals have been obtained with detection limits of 0.4 ppb, 2.5 ppb, 7.3 ppb, and 0.7 ppb for Cd (II), Pb (II), Cu (II), and Hg (II), respectively. Besides, the constructed sensor was successfully applied to simultaneously quantify target heavy metals in spiked water samples. Owing to excellent sensitivity, high robustness, affordability, and fast response, the presented electrochemical sensor could be incorporated into a portable and miniaturized potentiostat device, making it a promising method for on-site water analysis.     

Copper–mercury film electrode for cathodic stripping voltammetric determination of Se(IV)

The copper-mercury film electrode has been suggested for the determination of Se(IV) in a wide range of concentration from 1x10(-9) to 1x10(-6) mol L(-1)by square-wave cathodic stripping voltammetry. Insufficient reproducibility and sensitivity of the mercury film electrode have been overcome by using copper(II) ions during the plating procedure. Copper(II) has been found to be reduced and form a reproducible copper-mercury film on a glassy carbon electrode surface. The plating potential and time, the concentration of copper(II) and the concentration of the supporting electrolyte have been optimised. Microscopy has been used for a study of the morphology of the copper-mercury film. It has been found that it is the same as for the mercury one. The preconcentration step consists in electrodeposition of copper selenide on the copper-mercury film. The relative standard deviation is 4.3% for 1x10(-6) mol L(-1) of Se(IV). The limit of detection is 8x10(-10) mol L(-1) for 5 min of accumulation.     

Application of adsorptive cathodic differential pulse stripping method for simultaneous determination of copper and molybdenum using pyrogallol red

A reliable and sensitive procedure for the simultaneous determination of trace levels of copper and molybdenum is proposed. The complexing of copper(II) and molybdenum(VI) with pyrogallol red (PGR) is analyzed by cathodic stripping differential pulse voltammetry based on the adsorption collection of the complexes onto a hanging mercury drop electrode (HMDE). The effect of chemical and instrumental parameters on the sensitivity and selectivity were studied. Copper and molybdenum peaks potential were observed at about +0.13 and −0.22 V versus Ag/AgCl electrode, respectively. A standard addition method was utilized for the analysis of voltammogram data, under the optimum conditions and with accumulation time of 90 s. The measured peak current at about +0.14 and −0.22 V is proportional to the concentration of Cu(II) and Mo(VI) over the range of 2-70 and 0.8-80 ng ml⁻¹, respectively. The limit of detection are 0.3 and 0.1 ng ml⁻¹ for Cu(II) and Mo(VI), respectively. The capability of the method for the analysis of real samples was evaluated by determination of copper and molybdenum in river water, tap water and alloy. Atomic absorption spectrometry was applied as a reference method for determination of copper and molybdenum in water samples.     

Differential Pulse Anodic Stripping Voltammetric Simultaneous Determination of Copper(II) and Silver(I) with Bis(2‐hydroxyacetophenone) Butane‐2,3‐dihydrazone Modified Carbon Paste Electrodes

The behavior of a modified carbon paste electrode (CPE) for simultaneous determination of copper(II) and silver(I) by anodic adsorptive stripping voltammetry (ASV) was studied. The electrode was built incorporating the bis(2‐hydroxyacetophenone) butane‐2,3‐dihydrazone (BHAB) as a complexing agent to a Nujol‐graphite base paste. The resulting electrode demonstrated linear responses over the range of Cu(II) and Ag(I) concentrations 0.1–20 and 0.01–2.0 µM respectively. The relative standard deviation (RSD) for the determination of 5.0 µM of both metal ions were 2.9 and 3.1 % for Cu(II) and Ag(I), respectively. The method has been applied to the analysis of copper in wheat and barley seed samples and silver in developed radiological film.     

Simultaneous determination of cadmium(II), lead(II) and copper(II) by using a screen-printed electrode modified with mercury nano-droplets

We are presenting a strategy for the fabrication of disposable screen-printed electrodes modified with mercury nano-droplets and capable of sensing heavy metal ions. They were prepared by coating electrodes with a mixture of multi-walled carbon nanotubes and chitosan, this followed by adsorption of mercury. The resulting sensor was characterized by cyclic voltammetry and impedance spectroscopy. Also the effects caused by adsorption of mercury were investigated. It is shown that square wave anodic stripping voltammetry enables simultaneous determination of cadmium(II), lead(II) and copper(II), for which detection limits of 12, 23 and 20 nM, respectively, are found. Relative standard deviations for ten determinations at 0.6 µM concentrations of these ions are in the range of 3.0 to 5.7%. The applicability was tested by analyzing river water and showed recoveries between 94.1 and 104.6%, thus demonstrating its utility for in-field monitoring of these heavy metal ions.     

Accumulation voltammetry of copper(II) at carbon-paste electrode containing salicylideneamino-2-thiophenol

Summary Accumulation voltammetry of copper(II) was investigated with a carbon-paste electrode containing salicylideneamino-2-thiophenol(SATP). Copper(II) was accumulated as the copper(II)-SATP complex on the electrode without an applied potential by immersing the electrode in 0.01 mol/l acetate buffer (pH 3.8) containing copper(II). The reduction peak of the copper(II)-SATP complex was observed at –0.12 V (vs. SCE) in 0.01 mol/l acetate buffer (pH 3.8) by scanning the potential in a negative direction. The calibration curve for copper(II) was linear in the range of 2×10^–9–1×10^–7 mol/l. Since the accumulation of copper(II) is based on a chemical reaction between copper(II) and SATP, copper(II) was selectively accumulated on the electrode. The presented method was applied to the determination of copper(II) in standard reference materials prepared by the National Institute for Environmental Studies.     

Voltammetric determination of copper at chemically modified electrodes based on crown ethers

The feasibility of fabricating copper-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and in 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The electrodes so formed were able to bind Cu(II) ions chemically and gave better voltammetric responses than the unmodified ones. The crown ethers studied and compared were 15-crown-5, benzo-15-crown-5 and dibenzo-18-crown-6. With a 3% benzo-15-crown-5 CME, Cu(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.05 ppm. By differential pulse anodic stripping voltammetry Cu(II) could be quantified over the range I to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Fe(II), etc. have also been studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.