A liquid-state copper(II) ion-selective electrode containing a complex of Cu(II) with salicylaniline

A new liquid-state ion-selective electrode based on a complex of Cu(II) with salicylaniline is described. The electrode shows linear dependence of potential on the activity of Cu(2+) in the range from 5 x 10(-6) to 0.1M, with a slope of 28.3 mV/pCu at 18 degrees . The electrode shows a better selectivity relative to Ag(I) and Hg(II) than other copper(II) ion-selective electrodes. The possibilities for using the electrode for determination of copper in the presence of interfering cations are described.     

Effect of chloride ions on the behaviour of the orion copper(II) ion-selective electrode

The normal shiny surface of a copper(II) ion-selective electrode tarnishes when exposed to chloride ions. Polishing with fine emery cloth easily removes this dull surface layer and fully restores the proper potential response characteristics of the electrode. No such loss of character is evident with a non-chloride based reference electrode except in the presence of added chloride ions. The electrode also seems less affected in premixed solutions of copper(II) and chloride. the chloride ions then being largely bound as copper(II) chloro-complexes.     

Ionic medium effects on equilibrium constants Part I. Proton, copper(II), cadmium(II), lead(II) and acetate activity coefficients in aqueous solution

The molar single ion activity coefficients associated with hydrogen, copper(II), cadmium(II) and lead(II) ions were determined at 25 degrees C and ionic strengths between 0.100 and 3.00 M (NaClO4), whereas for acetate the ionic strengths were fixed between 0.300 and 2.00 M, held with the same inert electrolyte. The investigation was carried out potentiometrically by using proton-sensitive glass, copper, cadmium and lead ion-selective electrodes and a second-class Hg|Hg2(CH3COO)2 electrode. It was found that the activity coefficients of these ions (y(i)) can be assessed through the following empirical equations: log y(H) = -0.542I(0.5) + 0.451I; log y(Cu) = -1.249I(0.5) + 0.912I; log y(Cd) = -0.829I(0.5) + 0.448I(1.5); log y(Pb) = -0.404I(0.5) + 0.117I(2); and log y(Ac) = 0.0370I     

Preparation of an ion-selective electrode by chemical treatment of copper wire for the measurement of copper(II) and iodide by batch and flow-injection potentiometry

The preparation of an ion-selective electrode by chemical treatment of copper wire and its application for the measurements of copper (II) and iodide ions is described. The proposed reaction mechanism at the sensing surface, which explains the response of the electrode to Cu²⁺ and iodide ions, is discussed. The prepared electrode was suitable for direct potentiometric measurements of iodide and copper (II) in batch experiments down to concentrations of 1 × 10^–5 mol L^–1. A tubular electrode, prepared in the same way, may be used as a potentiometric sensor in a flow-injection analysis for Cu (II) and/or iodide determinations.     

Novel PVC-based copper(II) membrane sensor based on 2-(1'-(4'-(1'-hydroxy-2'-naphthyl)methyleneamino)butyl iminomethyl)-1-naphthol.

A copper(II) ion-selective PVC membrane sensor based on 2-(1'-(4'-(1'-hydroxy-2'-naphthyl)methyleneamino)butyl iminomethyl)-1-naphthol (BHNB) as a novel Schiff base containing a sensing material has been successfully developed. The sensor exhibits a good linear response of 29 mV per decade within the concentration range of 10(-1)-10(-6) M of Cu2+. The sensor shows good selectivity for copper(II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The BHNB-based sensor is suitable for use with aqueous solutions of pH 3.5-7.0 and displays minimal interference by Sr(II), Cd(II), Hg(II), Zn(II) and Pb(II), which are known to interfere with other previously suggested electrodes. The proposed membrane electrode was used as a sensor for determining the Cu(II) content in black tea samples. It was also applied as an indicator electrode in the potentiometric titration of Cu2+ ions with EDTA.     

Potentiometric behaviour of the copper electrode in aqueous copper(II) perchlorate solutions containing sodium chloride

It is demonstrated that the copper metal electrode corrodes in the presence of copper(II) ions in solution. A model based on mass balance can properly describe the experimental results. In the presence of copper(II) ions the copper electrode responds to copper(I), indicating that the electrode potential corresponds to a mixed potential.     

Preparation of an ion-selective electrode by chemical treatment of copper wire for the measurement of copper(II) and iodide by batch and flow-injection potentiometry

The preparation of an ion-selective electrode by chemical treatment of copper wire and its application for the measurements of copper (II) and iodide ions is described. The proposed reaction mechanism at the sensing surface, which explains the response of the electrode to Cu²⁺ and iodide ions, is discussed. The prepared electrode was suitable for direct potentiometric measurements of iodide and copper (II) in batch experiments down to concentrations of 1 × 10^–5 mol L^–1. A tubular electrode, prepared in the same way, may be used as a potentiometric sensor in a flow-injection analysis for Cu (II) and/or iodide determinations. Received: 4 December 1998 / Revised: 31 March 1999 / Accepted: 6 April 1999     

Diffusion-layer model for copper solid-state chalcocite membrane electrode; sensitivity to copper(II) ions

The diffusion-layer model for the chalcocite (Cu(2)S) membrane electrode is discussed. It is equivalent to a simpler model based on exchange reactions at the electrode surface. The chalcocite is sensitive to copper(I) and copper(II) ions and the theoretically predicted response is in good agreement with experimental data. The membrane is a conductor, but this does not significantly affect its function as an ion detector. The limitation of the electrode is the membrane solubility as shown when Cu(II) ions in contrast to copper(I) ions are strongly complexed.     

The behaviour of two types of copper ion-selective electrodes in different copper(II)-ligand systems

The behaviour of two types of solid-state homogeneous sensors for copper(II), one based on pressed pellets of ternary CuAgSe and the other on thin-layer electroplated Cu(2-x)Se, in 12 different copper(II)-ligand systems, has been thoroughly investigated. Both electrodes exhibit anomalous behaviour when the ligands are of complexone type, the effect of the complexones on the deviations increasing in the order IDA < NTA < EDTA approximately DTPA, and being practically the same for the two types of sensors, thus disproving a previous suggestion that the anomaly is due to the silver in the silver-containing sensors. The experimental data do not support the specific ligand-adsorption hypothesis either. The observed deviations are tentatively explained on the basis that, as suggested by the selectivity coefficients, both sensors act as primary copper(I) ion-selective electrodes rather than copper(II)-electrodes. Thus, at very low copper(II) concentrations, according to the extended Nikolskii equation, the [Cu(I)]/[Cu(II)] ratio at the electrode surface determines the electrode sensitivity towards Cu(II). The lower detection limit could be improved by pH-control and selective complexation of Cu(I). This hypothesis has been proved experimentally. If the copper(I) activity on the electrode surface is decreased, the anomaly observed for the Cu(II)-NTA system disappears and decreases considerably for the Cu(II)-EDTA and Cu(II)-DTPA systems.     

Potentiometric Characterization of Telomerase Activity Using a Copper(ii)-pyrophosphate Complex with a Copper ion-selective Electrode

A novel potentiometric sensing platform was designed for real-time electronic monitoring of telomerase activity using a copper(II) ion-selective electrode (Cu-ISE). The target-induced coordination of pyrophosphate ion with copper ion (Cu²⁺) was utilized for the detection of the enzyme activity. Upon telomerase introduction, a DNA primer was elongated in the presence of deoxyribonucleoside triphosphates, accompanying formation of the by-product (pyrophosphate ion; P₂O₇^4-). The generated pyrophosphate ions chemically coordinated with free copper ions to form the copper(II)-pyrophosphate complex, thereby resulting in a decrease in the number of free copper ions present in solution. With the addition of telomerase, the electrode potential on the Cu-ISE increased relative to the background signal. The results indicated that the copper(II)-pyrophosphate system exhibited good potentiometric response for the detection of telomerase activity, and allowed the determination of the analyte in HeLa cell extract at concentrations as low as 36 cells mL^?1. Moreover, the Cu-ISE-based sensing platform afforded good reproducibility, thus representing a useful approach for practical use in quantitative telomerase activity assays.     

Preconcentration of copper(II) on immobilized 8-quinolinol in a flow-injection system with an ion-selective electrode detector

A column containing 8-quinolinol, immobilized on porous glass, is used for preconcentration and medium exchange in a flow-injection system with a copper ion-selective electrode detector. The metal ions are bound to the chelating ion exchanger while the anions and inert sample components pass to waste without contacting the electrode. Acid is then injected to elute the ions into a neutralizing buffer passing the electrode. Matrix effects are thus reduced because all measurements are made in the same buffer. The detection limits are 10^?7 and 3 × 10^?8 M copper(II) for sample volumes of 5 and 25 ml, respectively. The maximum throughput is 12 and 5 samples h^?1 for the two stated injection volumes.     

Copper(I) sulphide-impregnated silicone rubber membranes as selective electrodes for copper(II) ions

Silicone rubber membranes impregnated with copper(I) sulphide have been developed as selective electrodes for coppefr(II) ions. The internal electrode and solution were eliminated. The Nernst equation was satisfied in the concentration range from 10(-1) to 10(-6)M copper(II) and the analytical range was from 10(-1) to 10(-7)M. The interference of other ions was examined. Other resins were compared with silicone rubber as inert matrices.     

Investigation of Copper(II) Interference on the Anodic Stripping Voltammetry of Lead(II) and Cadmium(II) at Bismuth Film Electrode

The bismuth‐coated electrode is known to be prone to errors caused by copper(II). This study investigates copper(II) interference at bismuth film electrode for the detection of lead(II) and cadmium(II). It was conducted using glassy carbon electrode, while the bismuth film was plated in situ simultaneously with the target metal ions at ? 1200 mV. Copper(II) presented in solution significantly reduced the sensitivity of the electrode, for example there was an approximately 70 % and 90 % decrease in peak signals for lead(II) and cadmium(II), respectively, at a 10‐fold molar excess of copper(II). The decrease in sensitivity was ascribed to the competition between copper and bismuth or the metal ions for surface active sites. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) analysis suggested a large decrease in the amount of bismuth nanoparticles formed on the electrode surface in the presence of copper(II) occurred, validating the competition between copper and bismuth ions for surface active sites. Recovery of the stripping signal of lead(II) and cadmium(II) was obtained by adding ferrocyanide ion to the solution. Finally, the proposed method was successfully applied to determine lead(II) and cadmium(II) in water samples and the method was validated by ICP‐MS technique.     

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.     

Copper ion-selective chalcogenide glass electrodes: Analytical characteristics and sensing mechanism

New copper ion-selective electrodes based on chalcogenide glasses, Cu_xAg_25?xAs_37.5Se_37.5, display high copper(II) ion sensitivity with Nernstian response in the range pCu 1–6, short response time, high selectivity, potential stability and reproducibility. These electrodes are 10–30 times more sensitive in strongly acidic media than crystalline copper ion-selective sensors and are superior to the copper(I) selenide electrode in selectivity and resistance to acids and oxidation. A model is proposed to explain the ion sensitivity of these chalcogenide glass sensors. The sensitivity depends on direct exchange of copper(II) ions between solution and the modified surface layer of the glass. The modified surface layer is formed as a result of partial destruction of the glass network on soaking in solution; its atomic density is 2.0–2.5 times less than that of the original glass. The structural defects and hollows make fast copper(II) ion migration within the modified surface layer possible. Exchange sites in this layer can be formed by both disproportionation and oxidation of copper(I) in the glass network, as well as by diffusion of copper(II) ion from solution in the case of glasses with low copper content. Experimental confirmation of this model is provided by x-ray, photo-electron and scanning Auger electron spectroscopy.     

New Copper(II) Ion-Selective Membrane Electrode Based on Erythromycin Ethyl Succinate as a Neutral Ionophore

Abstract

The potentiometric response characteristics of a new copper(II) ion-selective PVC membrane electrode based on erythromycin ethyl succinate (EES) as ionophore were investigated. The electrode exhibited a Nernstian response to Cu²⁺ ions over the activity range of 1.5 × 10^?2 to 2.0 × 10^?6 mol L^?1 with a limit of detection of 6.3 × 10^?7 mol L^?1. Stable potentials were obtained in the pH range of 5.5–6.5. The potentiometric selectivity coefficients were calculated by using fixed interference method and revealed no important interferences except for Ag⁺. This electrode was successfully applied as an indicator electrode in determination of copper ions in real water samples.     

Chloride interference with non-stoichiometric copper sulphide copper(II)-selective electrodes: Part 3. New equation for the electrode response

A general equation for the electrode potential response under metastable equilibrium conditions is derived for the non-stoichiometric copper sulphide electrodes immersed in solutions containing Cu(II) and Cu(I) and the interfering chloride ions. The theoretically predicted “anomalous” slopes (S_II = δ E/δ) log C_Cu(II) of the calibration curves, greater than 29.6 mV at 25° C, were confirmed experimentally in concentrated chloride solutions. The inapplicability of the Nicolsky equation for the electrodes at equilibrium is discussed on the basis of the theory presented. The new relationship (Eqn. 13) can be adapted for other ion-selective electrodes for which the exchange reactions with the solution species are fast enough and mass transport is not inhibited.     

The calibration and response of ion-selective electrodes at low concentrations of primary ions

Electrolytic generation of ions is proposed for the preparation of standard solutions for the calibration of iodide and silver ion-selective electrodes in the concentration range 10^-4–10^-7 M. The responses of these electrodes and also the copper(II) ion-selective electrode were examined in various electrolyte solutions. The current efficiencies of the electrolytic generation of the iodide ions into the various solutions were measured coulometrically. The advantages of this newly proposed calibration technique are discussed.     

On-line monitoring with an ion-selective electrode in a high-volume flow-through cell

A high-capacity poly(vinyl chloride) flow-through cell which can be used at a flow rate of 3000 ml min^-1 in a corrosive environment is described for the continuous on-line monitoring of copper ions in plant electrolytes. The copper(II) ion-selective electrode and double-junction reference electrode in the cell are coupled to a voltmeter and microprocessor-controlled instrumentation to achieve on-line monitoring. The system is designed to withstand the severe industrial environments and was field-tested in a copper refinery where continuous monitoring of copper is required. Cell design and results of the investigation on the determination of copper in plant electrolytes are described.     

Processing of signals from an ion-elective electrode array by a neural network

Neural network software is described for processing the signals of arrays of ion-selective electrodes. The performance of the software was tested in the simultaneous determination of calcium and copper(II) ions in binary mixtures of copper(II) nitrate and calcium chloride and the simultaneous determination of potassium, calcium, nitrate and chloride in mixtures of potassium and calcium chlorides and ammonium nitrate. The measurements for the Ca²⁺/Cu²⁺ determinations were done with a pH-glass electrode and calcium and copper ion-selective electrodes; results were accurate to ±8%. For the K⁺/Ca²⁺NO^?₃/Cl^? determinations, the measurements were made with the relevant ion-selective electrodes and a glass electrode; the mean relative error was ±6%, and for the worst cases the error did not exceed 20%.