The behaviour of copper(II)-selective electrodes in chloride-containing solutions

Calibration curves for copper(II) in solutions containing various chloride ion concentrations are examined in detail. The mechanism of the interferences on the behaviour of the copper(II)-selective electrode is discussed. The anomalous slopes observed can be explained by considering the sensitivity of the electrode membrane to the silver ions released from the electrode surface by chemical interaction with the solution. The effects of the formation of silver-chloride complexes and of the changes in the membrane are described.     

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.     

Application of a wall jet disk electrode combined with an electrochemical quartz crystal microbalance to the study of the dissolution of copper in acidic chloride media

An electrochemical quartz crystal microbalance (EQCM) system combined with a wall jet disk electrode (WJDE) was applied to the investigation of copper dissolution in acidic chloride media. The average valence of dissolved ions, n, was calculated from the resonant frequency of the quartz crystal and the applied current. The value of n between 1 and 2 indicates that both Cu(I) and Cu(II) dissolved from the copper electrode at the same time. The formation rate of Cu(II) increased with decreasing chloride concentration. The influence of the hydrodynamic conditions on the dissolution behaviour was discussed.     

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.     

Copper(I) activity of the copper(II) ion-selective electrode

The Orion copper(II) ion-selective electrode responds well to copper(II) ions in aqueous medium. However, in the presence of acetonitrile and copper(I) ions, it can behave as a copper(I) ion-selective electrode with Nernstian behaviour.     

Changes in surface stress of gold electrode during underpotential deposition of copper

The changes in surface stress of the evaporated gold electrode (mainly oriented to the (111) plane) during underpotential deposition (UPD) of copper in 0.1 M sulfuric acid medium or 0.1 M perchloric acid medium with and without sulfate or chloride were measured using a bending beam method. The surface stress maximum of gold electrode appeared during Cu-UPD. The co-adsorption of (bi)sulfate or chloride ions with copper atoms induced the compressive surface stress to promote the Cu-UPD. The factors influencing the surface stress or surface elastic strain were discussed in relation to the Cu-UPD structure. Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.     

Determination of traces of purine by cathodic stripping voltammetry at the hanging copper amalgam drop electrode

In the presence of purine, the copper(II)/copper(Hg) couple splits into copper(II)/copper(I) and copper(I)/copper(Hg) couples, which form two well-separated systems of peaks under voltammetric conditions. The copper(I)/purine complex adsorbs on the electrode surfacer and can be deposited on the electrode surface by electroreduction of copper(II) ions at the HMDE or by electro-oxidation of the hanging copper amalgam drop electrode (HCADE). The deposit can be stripped either cathodically or anodically over the pH range 2–9. The cathodic stripping variant at the HCADE, in solution with pH 2, offers the best results, with linear response for the range 5 × 10^?9–1.5 × 10^?7 mol dm^?3 purine after an accumulation time of 3 min. The detection limit found with the HMDE in the presence of copper(II) ions is higher.     

Investigations into the electroreduction of copper(II) ions on chalcocite in ammonia solutions using the rotating disc electrode method

Investigations into the electroreduction of copper(II) ions in ammonia solutions on a disc electrode made of synthetic chalcocite having a deficiency of copper atoms have been presented. It has been concluded that within the range of the diffusion controlled process copper(II) ions are the diffusing substance, at the same time in the course of the reaction two electrons are exchanged. The kinetic parameters for the electroactivating process have been estimated. With a higher concentration of copper in solution an inhibition process has been observed, probably caused by a slow transport rate of the species in the material of the electrode. In the system studied the phenomenon of a partially blocked electrode surface does not occur according to the Landsberg model.     

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.     

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     

Copper in Acid Chloride Solutions: Electrochemical Behavior by Quartz Microgravimetry and Voltammetry

The cathodic deposition of copper on a gold electrode and its subsequent anodic dissolution in an acid chloride solution, where two successive stages of a one-electron transfer are distinguishable because of the stability of chloride complexes of Cu(I), is studied by voltammetry and quartz microgravimetry. The formation of a film of an intermediate compound of Cu(I) during the deposition and dissolution of copper is revealed experimentally. Techniques for identifying the intermediate solid species are suggested. During a cathodic polarization, a film of intermediate compound CuCl forms at a reduced concentration of chloride ions in the Cu(II)/Cu(I) process, while during the anodic dissolution of the copper deposit formed during the cathodic polarization the intermediates appear in the Cu(0)/Cu(I) process, the concentration of chloride ions notwithstanding. The change in the electrochemical behavior of the system caused by a decrease in the concentration of chloride ions is explained.     

Chloride interference with non-stoichiometric copper sulphide coppers-selective electrodes : Part 1. Mechanisms

The behaviour of copper(II)-selective electrodes made of non-stoichiometric copper sulphide single crystals is discussed. The mechanism of chloride ion interference with the electrode operation is considered on the basis of potentiometric and dynamic measurements. The occurrence of irreversible processes at the electrode surface is described.     

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.     

Effect of anion adsorption on early stages of copper electrocrystallization at Au(111) surface

The monolayer and submonolayer deposition of copper on Au(111) electrode surface in the presence of chloride and sulfate ions was studied by in situ X-ray absorption and electrochemical techniques. The anions coadsorb with the deposited copper adatoms and have a strong influence on the structure of these mixed overlayers. Copper deposited in the presence of chloride forms a bilayer in which copper atoms are sandwiched between the gold substrate and the top layer of chloride ions. The bilayer is well ordered and has a (5×5) long range structure. The copper atoms are packed in registry with the top layer of chloride ions. In contrast, copper adatoms deposited in the presence of sulfate ions are packed in registry with respect to the Au(111) substrate. The coadsorbed copper and sulfate form a highly corrugated overlayer. The copper adatoms assume a honeycomb (√3×√3) structure with the center of the honeycomb occupied by sulfate. The sulfate ion adsorbs with three of its four oxygens directed towards the hexagon of copper adatoms. The bond angle between the copper adatom and the oxygen of the sulfate ion is approximately equal to 45 °. Our data indicate that, in contrary to the literature reports, the (√3×√3) structure observed on STM and AFM images corresponds to the corrugation of adsorbed sulfate ions rather than copper adatoms.     

Variability of selectivity coefficients of solid-state ion-selective electrodes

The generalized model for the selectivity mechanism of solid-state ion-selective electrodes has been experimentally verified. The experimental parameters investigated were the concentration of interfering ion, temperature and stirring. Among the systems studied were electrodes sensitive to chloride (bromide, iodide), bromide (chloride, iodide), iodide (chloride, bromide), silver (copper, lead), copper (silver, lead) and lead (silver, copper), the species given in brackets being considered as the interferents. The model has been confirmed except for cases where the concentration of ions formed at the electrode surface by metathesis is too small to be the factor that dictates the electrode potential.     

Experimental and computational study of species formed during electrochemical stripping oxidation of copper in chloride media determination of copper(II) in the ng l(-1) range by stripping potentiometry

A novel glassy carbon electrode design, permitting medium exchange in batch mode without loss of electrode potential control, has been used for the study of copper(I) and copper(II) species formed during constant current stripping oxidation of copper in chloride media. It was found that copper(II) species dominated at chloride concentrations below about 1 mM and that soluble copper(I) species dominated at chloride concentrations above about 100 mM. In the concentration range 1-100 mM, soluble copper(I) and copper(II) species are formed as well as solid copper(I) chloride, the latter giving rise to a split peak as it is further oxidised to copper(II). The experimental results agreed satisfactorily with computer calculated equilibria data using the haltafall program. The medium exchange procedure has, furthermore, been used for the determination of copper(II) in seawater reference samples, 7.5 M ammonium acetate/2.5 M acetic acid being used as stripping medium. The detection limit, after 15 min of electrolysis, was found to be 6 ng l(-1) (0.10 mM) and the relative precision 6-10%.     

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.     

Copper(II)-selective electrode using 2,2'-dithiodianiline as neutral carrier

Poly(vinyl chloride) membrane electrode, that is highly selective and sensitive to Cu(II) ions, was developed by using 2,2'-dithiodianiline and dibutyl phthalate as carrier and plasticizer, respectively. The electrode exhibits good potentiometric response for Cu(II) over a wide concentration range (5.0x10(-2)-7.0x10(-7) mol l(-1)) with Nernstian slope of 30+/-1 mV per decade. The response time of the electrode is 10 s and it has been used for a period of one month and exhibits good selectivity towards Cu(2+) in comparison to alkali, alkaline earth, transition and heavy metal ions, with no interference caused by Pb(2+), Cd(2+) and Fe(+2) which are known to interfere with many other copper electrodes.     

The influence of some organic complexing agents on the potential of copper(II) - selective electrodes. application of the silicone rubber-based electrode to the determination of citrate ion and 8-hydroxyquinoline

The behaviour of the silicone rubber-based copper(II)-selective electrode in the presence of complexing agents is discussed. The electrode shows well defined responses to several complexing agents in solutions practically free of copper(II) ions. Titrimetric determinations of citrates and 8-hydroxyquinoline with potentiometric end-point detection are described.