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.     

Adsorptive stripping voltammetric behaviour of copper complexes of some heterocyclic azo compounds

Controlled adsorptive accumulation of copper complexed with TAN, TAC, TAR and TAM (heterocyclic azo-compounds) on a static mercury drop electrode provides the basis for the direct stripping measurement of this element in the nanomolar concentration level. The ligand TAN exhibited great sensitivity and better separation of the peak current of the ligand in relation to the complex. The reduction current of adsorbed complex ions of copper is measured by linear scan cathodic stripping voltammetry, preceded by a period of accumulation of a few minutes. The peak potential is at approximately -0.37 V vs. Ag/AgCl. Optimal experimental parameters were found to be a TAN concentration of 1 x 10(-5)M, an accumulation potential of -0.22 V, and a solution pH of 3.7 (acetate buffer). The detection limit is 0.8nM after a 5-min accumulation with a stirred solution, and the response is linear up to 50 mug/l. Many common cations and anions do not interfere in the determination of copper. The interference of titanium is eliminated by addition of fluoride ion. Results are reported for a fresh water sample.     

Application of gallium film electrode for elimination of copper interference in anodic stripping voltammetry of zinc

For elimination of copper interference in anodic stripping determinations of zinc at mercury and bismuth film electrodes gallium ions are usually added to the supporting electrolyte. In the presented studies novel ex situ formed gallium film electrode was applied for this purpose. The proposed electrode is less toxic than mercury one while the detection limit for zinc was lower than for bismuth film electrode following the same deposition time. The calibration graph for deposition time of 60 s was linear from 5 × 10⁻⁸ to 2 × 10⁻⁶ mol L⁻¹. The determinations of zinc were carried out from undeaerated solutions. The proposed procedure was applied to zinc determination in certified reference material and tap water sample.     

Release of copper from commercial solid-state copper ion-selective electrodes

The release of copper from two commercial solid-state cupric ion-selective electrodes [Orion 94-29 Cupric Electrode (I) and Radiometer F1112 Selectrode (II)] was measured by immersion in the following media: 0.1M potassium nitrate (pH = 4.7), 0.5M sodium chloride (pH = 4.7) and 0.1M nitric acid. In the 0.1M potassium nitrate medium, the amount of copper released from both electrodes causes interference when they are used for the determination of cupric ion at the 10⁻⁷M level. In comparison with the 0.1M potassium nitrate medium, the copper release in the 0.5M sodium chloride and 0.1M nitric acid media was increased for electrode II but not for electrode I. The release of copper was not affected by removal of oxygen from the media but can be substantially lowered by coating the electrodes with a thin cation-exchange membrane (Nafion). The mechanism of copper dissolution is investigated.     

The chalcocite copper membrane electrode

The membrane electrode based on a synthetic chalcocite (Cu(2)S) single crystal responds primarily to the activity of copper(I) ions in solution. The experimental selectivity coefficient with respect to copper(II) ions is in good agreement with the value calculated on the basis of solubility products of both sulphides. The electrode has been calibrated with metal-ion buffers containing a strongly complexing ligand. TETREN, and can be used as an indicator in titrations of copper with EDTA and TETREN. Comparison of an experimental titration curve with one calculated with the aid of the program HALTAFALL showed good agreement in the case of TETREN, but there were discrepancies for the EDTA titration, which are attributed to the presence and complexation of copper(I) ions. The electrode has also been applied in metal titrations with Cu(2+) as indicator ion, though the potential changes observed were smaller than predicted. All titrations showed errors less than 1%.     

Voltammetric measurement of copper(II)/organic interactions in estuarine waters

The voltammetry of copper in organic ligand/chloride media is dominated by the formation of CuCl^?₂ species and by induced adsorption of Cu(I) in organic coatings on the electrodes. These phenomena are utilised in a novel method for evaluating Cu(II)/organic ligand interactions, based on the principle of ligand exchange. The Cu(II)/organic species competes with glycine which forms copper glycinate. These two complexes can be distinguished voltammetrically: copper glycinate gives a higher surface excess of copper at a gelatin-coated hanging mercury drop electrode, partly because of the increased production of CuCl^?₂ from copper glycinate at the electrode surface. The method proved satisfactory for pure ligand/surfactant/chloride media and for estuarine waters. It is shown that there are two type of Cu(II)-binding ligand in estuarine waters: humic material (> 10^?6 mol l^?1, assuming 1:1 site binding) with polyelectrolyte-type binding, and discrete ligands (? 10^?6 M) with stability constants around 10⁹. The extent of Cu(II) binding by the humic material decreases down the estuary because of dilution and increased salinity.     

Voltammetric studies of purine bases and purine nucleosides with copper

Anodic stripping voltammetry with a hanging mercury drop electrode has been used to investigate the interaction of cooper with the purines adenine, hypoxanthine, xanthine and purine nucleosides adenosine, guanosine and inosine at an ionic strength of 0.1 M in KNO₃ and in the pH range 3.5–5.5. In all cases stabilisation of copper(I) occurs suggesting that the oxidation of copper(0) in the presence of excess ligand proceeds in two one-electron steps.Adsorption onto the electrode has been analysed and conditions where this is negligible were chosen for complexation studies. From the shift of the peak potential corresponding to Cu(0)/Cu(I) oxidation with increasing ligand concentration the stoichiometry of the complexes and their formation constants have been determined. The values obtained are discussed in terms of the ligand structure.     

Electrochemically driven reversible solid state metal exchange processes in polynuclear copper complexes

The electrochemical characteristics of polynuclear di-copper and tetra-copper complexes of an expanded "Robson-type" macrocyclic ligand are explored by solid state voltammetry in aqueous media. When adhered to a graphite electrode surface in the form of microcrystalline powders and immersed in aqueous buffer solution, these water-insoluble polynuclear copper complexes show well-defined voltammetric reduction and re-oxidation responses. The di-copper metal complexes [Cu₂(H₃L)(OH)][BF₄]₂ and the tetra-copper complexes [Cu₄(L)(OH)][NO₃]₃ with an O₄N₄ octadentate macrocyclic ligand L are shown to exhibit inter-related and proton concentration sensitive solid state voltammetric characteristics. At sufficiently negative potential, copper is extracted from the complexes to form a solid copper deposit and the neutral form of the insoluble free ligand. Upon re-oxidation of the copper deposit, Cu²⁺ undergoes facile re-insertion into the ligand sphere to re-form solid di- and tetra-copper complexes at the electrode surface. The reduction process occurs in two stages, with two Cu²⁺ cations being extracted in each step. The ability of the macrocyclic ligand to efficiently release and accumulate copper is demonstrated. Electronic Publication     

Potentiometric detection in ion chromatography using a metallic copper indicator electrode

Summary A metallic copper electrode housed in a suitable flowcell is shown to be a sensitive and versatile potentiometric detector for ion chromatography. This electrode may be used for direct or indirect detection of many inorganic anions and cations and also for organic acids. In the direct detection mode, electrode response is based on either complexation of copper ions at the electrode surface by eluted species, or on oxidation and reduction reactions for eluted species which are strong oxidants or reductants. Direct detection is therefore applicable to such species as amino acids, organic acids, chloride, bromide, iodide, chlorate, bromate and iodate. Indirect detection is possible for anions which do not complex copper ions, provided a copper complexing ligand (such as phthalate) is used in the eluent; cations which complex this ligand are also detectable. Indirect detection may be used for species such as nitrite, nitrate, acetate, formate, succinate, benzoate, alkaline earth ions and transition metal ions. Electrode calibration relationships are discussed and sample separations are presented, together with some typical detection limits attainable in the direct and indirect detection modes.Presented in part at a National Symposium on Ion Chromatography, held at the University of New South Wales, Kensington, Australia, Nov. 21, 1984.     

Evaluation of bathocuproine for the spectro-photometric determination of copper(I) in copper redox studies with applications in studies of natural waters

Copper(I) is determined at submicromolar levels in the presence of copper(II) in aqueous media by spectrophotometric measurement of the copper(I) complex of bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline). Copper(II) interference produced by reduction to copper(I) is described. Ethylenediamine can serve as a masking ligand to inhibit Cu(II) interference. The limit of detection is 1 × 10^?8 mol l^?1. Although this is not sensitive enough for use at natural copper concentrations, the procedure can be used in laboratory studies of copper redox processes at elevated levels in natural waters such as sea water. The dependence of results on pH and ionic strength was studied to evaluate the usefulness of the method in other aqueous systems.     

Sonoelectroanalytical detection of lead at a bare copper electrode

The sonochemically facilitated, mercury free detection of Pb2+ at a copper electrode has been investigated as a means of simplifying the quantification of this important analyte and to minimise the interference of copper ion. The procedure relies upon maximising the formation of Pb-Cu intermetallic compounds leading to the emergence of a single, easily quantifiable stripping signal. Linear responses to Pb2+ were obtained with a sensitivity comparable to that obtained at a bare glassy carbon electrode. Interference from Cu2+, Zn2+ and Cd2+ was assessed on the copper electrode with no appreciable change in the Pb2+ voltammetric profile observed. In contrast, bare glassy carbon showed a significant change in Pb2+ voltammetric profile as Cu2+ was added, due to the formation of intermetallic species.     

The Preparation of a Novel Polymer Film Based on Salicylaldoxime and its Influence on Aqueous Copper Electrochemistry

Abstract

The metal complexing ligand salicylaldoxime was electropolymerised onto platinum electrodes and the resulting film characterised by reflectance FT-IR spectroscopy. The modified electrode response to aqueous iron, copper, cobalt and lead ions was investigated with the iron(III) and copper(II) ions showing significantly altered electrochemistry. The response of the modified electrode towards aqueous copper ion was found to be directly proportional to copper concentration with little interference from lead ions. The retention of copper ions, film stability and the nature of the film action are discussed along with its potential use in sensor construction.     

Determination of copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

Effect of some chelating ligands on the potential response of the chalcocite copper ion-selective electrode

The effects of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, aminoacetic acid, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminediaminetetraacetic acid, diethylenetriaminepentaacetic acid and triethylenetetraminehexaacetic acid on the behaviour of the synthetic chalcocite (copper(I) sulphide) copper-selective electrode are described. The effects of those ligands on the electrode response at different pH values is explained on the assumption that copper(I) ions contribute to the potential indicated. Copper(I) ions originate from the membrane phase and participate in exchange and redox reactions. The effects of oxygen and temperature are reported. The electrode response can be predicted on the basis of copper(II) equilibria in solution, only if the conditions are such that there is no interference from copper(I) ions.     

Voltammetry of copper species in estuarine waters induced adsorption of copper on the hanging mercury drop electrode in complexing ligand/surfactant/chloride media

The adsorption of copper species on a positively charged hanging mercury drop electrode in complexing ligand/surfactant/chloride solution is discussed. Techniques used were differential pulse voltammetry of the copper in the adsorbed film, and potential-step reduction of adsorbed copper followed by different pulse anodic stripping voltammetry of Cu(Hg). The CuCl^?₂ species is shown to be the most important copper moiety adsorbed on the electrode and the adsorption is enhanced by organic films. This can be a critical pathway in the reduction of copper(II) in estuarine waters. The induced adsorption of copper in organic layers has biogeochemical implications associated with the nature of organic films and their influence on the Cu(II)/Cu(I) redox couple. There are also analytical applications, e.g., the compositional assay of organic monolayers by utilising Cu(II) and Cu(I) adsorption as electoractive probes and the determination of solution copper-organic binding.     

Surface chemistry and potential response of copper sulfide based ion-selective membrane in ligand solutions

Dissolution of membraneous composite ions of copper sulfide precipitate-based ion-selective electrodes (ISEs) has been measured in various ligand solutions by ICP atomic emission spectrometry and atomic absorption spectrometry from the solution side and by X-ray photoelectron spectrometry on the electrode surface. Asymmetric dissolution, amount of copper dissolved is higher than that of sulfur, was generally observed. The copper dissolution is correlated with the potential response as well as conditional stability constants. The results are discussed in terms of the charge separation caused by the asymmetric dissolution and electrostatic interaction of charged ligands with the space charge on the electrode surface in view of microscopic characterization of ISEs in metal buffer solutions in general. The results were also used to clarify the reason for some discrepancies of complex stability constants obtained by precipitate-based ISEs and other methods.Dedicated to Professor W. Simon on the occasion of his 60th birthday     

Voltammetric copper(II) determination with a montmorillonite-modified carbon paste electrode

The clay mineral montmorillonite has been tested as modifier for the carbon paste electrode with a novel electrode modification technique. The differential pulse voltammetric determination of copper(II) by means of this modified carbon paste electrode has been studied. A detection limit of 4x10(-8) mol/l has been achieved after 10 min preconcentration under open circuit conditions with subsequent anodic stripping voltammetry. The calibration curve for Cu(II) is linear in the range of 4x10(-8)-8x10(-7) mol/l. Pb interferes in a 10-fold molar and Cd and Hg in a 100-fold molar excess. The interference by humic ligands is significant.     

Resolving the copper interference effect on the stripping chronopotentiometric response of lead(II) obtained at bismuth film screen-printed electrode

As copper(II) is a common ion in a variety of analytical samples, its effect on the stripping response of lead(II) at bismuth film screen-printed carbon electrode (BFSPCE) was investigated. The study was conducted using a screen-printed three-electrode system (working, counter and reference electrodes), with the carbon-working electrode plated in situ with bismuth film. Copper present at significant concentration level in samples was found to affect the sensitivity of the electrode by reducing the constant current stripping chronopotentiometric (CCSCP) response of lead(II). Recovery of the lead stripping response at the BFSPCE in the presence of copper was obtained when 0.1 mM ferricyanide was added to the test solution. The ferricyanide added circumvents the detrimental effect of copper(II) by selectively masking the copper ions by forming a complex. The analytical utility of the procedure is illustrated by the stripping chronopotentiometric determinations of lead(II) in soil extracts.     

Elimination of iron interference in the differential pulse anodic stripping voltammetry of copper

The interference of iron(III) on the quantitation of copper(II) in citrate media by differential-pulse anodic stripping voltammetry can be completely removed by lowering the pH to 1.5 with 70% perchloric acid.     

Ion-sensitive behaviour of silver sulphide-based solid-state copper(II) and iodide electrodes in partially aqueous systems

The response of copper(II)- and iodide-selective electrodes was evaluated in various water-organic solvent mixtures. The copper(II) electrode showed an almost Nernstian behaviour in mixtures with ethylene glycol, tert-butanol, propanol, ethanol and methanol. The experimental slopes in buffered water-acetonitrile mixtures were linear but super-Nernstian. The response of this electrode in mixtures with p-dioxane was neither Nernstian nor linear. The interference of mercury(II) in the direct potentiometric titration of copper(II) with EDTA in solution containing acetonitrile was studied. The behaviour of silver sulphide-based iodide electrode hydrophobized by PTFE in mixtures with ethanol, methanol and p-dioxane was poorer than in water. The potential response of the iodide electrode with a homogeneous membrane (Ag₂S + AgI) was satisfactory even after prolonged soaking in p-dioxane.