Determination of copper(II) in a complex matrix after prereduction to copper(I) in a flow-injection system with an amperometric detector

A flow-injection system with a carbon paste detector is proposed for the determination of copper in complex media at +0.050 V vs. Ag/AgCl. Both the reduction current peak of Cu(II) and the oxidation peak of Cu(I) (obtained in the presence of hydroxylamine in the reagent stream) were proportional to the Cu(II) concentration in the original sample. The stabilization of Cu(I) in the hydroxylamine system provides a novel approach; the inherent repeatability of operation of flow-injection systems (timing, etc.) proved ideal for this utilization. Acidified Cu(II) samples containing additional metal ions [Fe(lI), Zn(II), Pb(II)] and relatively high concentrations of serum albumin were analysed. A chelating column retained heavy metal ions while allowing albumin to run to waste. The retained metals were subsequently eluted with nitric acid into a stream of sodium acetate or sodium acetate-hydroxyl- amine. Before reaching the detector, the pH of the sample plug was adjusted. With the hydroxylamine system, Fe(III) interference was minimized and the sensitivity and reproducibility were improved. The sample throughput was 25 h^?1. National Bureau of Standards Standard Reference Material 909 Human Serum was used to test the method.     

Calixazacrown ethers for copper(II) ion-selective electrode

Five novel 1,3-alternate calix[4]azacrown ethers having 2-picolyl, 3-picolyl, and benzyl unit on the nitrogen atom were synthesized and used as ionophores for transition metal-selective polymeric membrane electrodes. The electrode based on 2-picolyl armed 1,3-alternate calix [4] azacrown ether exhibited Nernstian response toward copper (II) ion over a concentration range (10(-4.5) M-10(-2.5) M). The detection limit was determined as 10(-5) M in pH 7 and the selectivity coefficients for possible interfering cations were evaluated. Anions in the sample solution strongly affected the electrode response.     

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.     

Kinetic influences on studies of copper(II) hydrolysis by copper ion-selective electrode

The hydrolysis of micromolar solutions of copper(II) is dominated by the formation of a copper—hydroxy colloid, both in the presence and absence of atmospheric carbon dioxide. Presence of the colloid was inferred from the response of the copper ion-selective electrode and confirmed by light scattering measurements. The colloid is only slowly converted to thermodynamically more stable species, with the result that copper—carbonate complexes are not formed to any significant extent in solutions exposed to atmospheric carbon dioxide. However, copper—carbonate complexes are formed in solutions containing a constant amount of total carbonate. Speciation and complexation capacity measurements should be interpreted with caution because thermodynamic equilibrium may not be attained in solution.     

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.     

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     

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.     

Chemically modified reticulated vitreous carbon electrode with immobilized enzyme as a detector in flow-injection determination of glucose

The construction and response of a chemically modified electrode in which glucose oxidase (E.C. 1.1.3.4) is covalently attached to the surface of reticulated vitreous carbon is reported. Hydrogen peroxide produced by the oxidation of glucose is consumed at the electrode suface, which is held at + 0.9 V vs. a saturated calomel reference electrode. The hydrodynamic and electrochemical properties of the reticulated vitreous carbon electrode substrate make the electrode attractive for use in flow systems. The current varies nonlinearly with glucose concentration throughout most of the range examined (10^?1?10^?4 M). At concentrations of 2.5–10 mM, response is approximately linear with concentration, with a sensitivity of about 400 nA mM^?1. Relative standard deviation for five sample at 10 mM^?1 is less than 2%.     

Flow injection analysis for residual chlorine using Pb(II) ion-selective electrode detector

A simple flow injection analysis (FIA) system for residual chlorine in tap water has been developed by using a Pb(II) ion-selective electrode (ISE) detector. The method is based on a specific response of the Pb(II)-ISE to residual chlorine. The FIA system consists of a millivolt meter, a peristaltic pump, a Pb(II)-ISE detector and a recorder. A linear working curve between peak height and concentration of residual chlorine was obtained from 0.1 to 1 mg l(-1) for the developed FIA system. The relative standard deviation for repeated injections of a 0.2 mg l(-1) residual chlorine sample was 2%. The regression line and its correlation factor between the conventional o-tolidine colorimetric method and the present method were Y=0.75X+0.17 and 0.967, respectively, for this determination.     

Cobalt(II) ion-selective electrode with solid contact

A new all plastic sensor for Co²⁺ ions based on 2-amino-5 (hydroxynaphtyloazo-1′)-1,3,4 thiadiazole (ATIDAN) as ionophore was prepared. The electrode exhibits a low detection limit of 1.5 × 10⁻⁶ mol L⁻¹ and almost theoretical Nernstian slope in the activity range 4.0 × 10⁻⁶–1 × 10⁻¹ mol L⁻¹ of cobalt ions. The response time of the sensor is less than 10 s and it can be used over a period of 6 months without any measurable divergence in potential. The proposed sensor shows a fairly good selectivity for Co(II) over other metal ions. The electrode was successfully applied for determination of Co²⁺ in real samples and as an indicator electrode in potentiometric titration of Co²⁺ ions with EDTA.      

Potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate film-modified electrode

A potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate(III) (CHCF) film-modified glassy carbon electrode is proposed. The electroactive film is introduced onto the glassy carbon electrode surface by electrodeposition of cobalt, which forms a thin CHCF film on subsequent anodic scanning in KClHCl solution (pH 5.0–5.5) containing K₃Fe(CN)₆. The thickness of the film on the electrode surface can be controlled by changing the electrodeposition time and the concentrations of cobalt(II) and Fe(CN)^3?₆ ions. The modified electrode exhibits a linear response in the concentration range 1 × 10^?1 ?3 × 10^?5 M potassium ion activity, with a near-Nernstian slope (48–54 mV per decade) at 25 ± 1°C. The detection limit is 1 × 10^?5 M. The stability, response time and selectivity were investigated. The electrode exhibits good selectivity for potassium ion with the twelve cations investigated. The relative standard deviation is 1.5% (n=10). The effects of the thickness of the electroactive film and the pH of the solution on the electrode response were also investigated.     

Response of the jalpaite membrane copper(II) ion-selective electrode in marine waters

The response of the Orion 94-29 Cu^II ion-selective electrode (ISE) [employing a jalpaite membrane] in seawater has been related to levels of free Cu^II yielding results for the Derwent River and San Diego Bay that are 2 to 3 orders of magnitude higher than those for the Pacific Ocean. Response data for the electrode in acidified seawater at pH 2 are internally consistent with total Cu^II levels determined using differential pulse anodic stripping voltammetry (DPASV) and graphite furnace atomic absorption spectrometry (GFAAS). It has been found that, even in acidified seawater, the organic ligands influence the response of the electrode, and this effect can be compensated successfully by either analyzing UV-photooxidized seawater and/or using a standard addition technique. The assigned ISE results for total Cu^II in acidified seawater fall within ± (0.1–0.5) pCu unit of values determined using GFAAS. Electrode drift in seawater can be minimized by using a polished electrode that has been conditioned in seawater for 24 h. The improved response rate of a conditioned ISE minimizes electrode soaking times and sample contamination through membrane corrosion.     

On-line trace metal enrichment and matrix isolation in atomic absorption spectrometry by a column containing immobilized 8-quinolinol in a flow-injection system

Metal ions (Cu²⁺, Co²⁺, Cd²⁺, Ni²⁺, Pb²⁺, Zn²⁺) were concentrated quantitatively and isolated from the sample matrix by a colum     

Determination of stability constant of copper(II) with thiosemicarbazide by use of a cupric ion-selective electrode

The stability constant of copper(II)—thiosemicarbazide complex has been determined potentiometrically by means of a cupric ion-selective electrode. Value of logK_CuL2 obtained in 0. 1 M KNO₃ at 25 °C corresponded well with the values given in the literature measured spectrophotometrically.     

Amperometric detection of amino acids in a flow-injection system with a nickel(II)-modified electrode with an Eastman-AQ polymer film

Amperometic flow measurements were made at +0.55 V (vs. Ag/AgCl) in 0.1 mol l⁻¹ KOH electrolyte with an Ni(II) chemically modified electrode (CME) with an Eastman-AQ polymer film. The use and characteristics of a Ni(II)-containing crystalline and polymer-modified electrode obtained by a double coating step as a detector for amino acids in a flow-injection system using reversed-phase liquid chromatography are described. The detection of these analytes is based on the higher oxidation state of nickel (NiOOH) controlled by the applied potential. The electroanalytical parameters and the detection current for a series of amines and amino acids were investigated. The use of such a CME in the flow-injection technique was found to be suitable in a solution at low pH. The linear range for glycine is 5 × 10⁻⁶-0.1 mol l⁻¹ with a detection limit of 1.0×10⁻⁶ mol l⁻¹. A 1 × 10⁻⁴ mol l⁻¹ mixture of serine and tyrosine was also detected after separation on an Nucleosil C₁₈ column.     

Response of a copper(II) and iron(III) ion-selective electrode bielectrode array in saline media

A bielectrode array comprising a jalpaite membrane (i.e., Ag_1.5Cu_0.5S) copper(II) ion-selective electrode (ISE) and chalcogenide glass membrane (i.e., Fe_2.5(Se₆₀Ge₂₈Sb₁₂)_97.5) iron(III) ISE has been assembled by individually wiring each solid-state sensor into a single electrode body. Furthermore, a dual metal ion buffer calibration standard incorporating copper(II) and iron(III) coordinating ligands to regulate the levels of free copper(II) and iron(III) in the buffer has been developed to enable simultaneous calibration of the bielectrode ISE array. In this work, the bielectrode ISE array has been employed in the continuous flow analysis (CFA) of free copper(II) and iron(III) in seawater media. It is shown that the individual electrodes displayed Nernstian response in the metal ion buffer calibration standard over a wide dynamic range (viz., 10⁻¹⁵ to 10⁻⁵ M aCu²⁺ and 10⁻²¹ to 10⁻¹¹ M aFe³⁺), and the results of repetitive CFA analyses of free copper(II) and iron(III) in seawater are commensurate with the typical values found in coastal seawater samples. Clearly, the bielectrode ISE array may be used in the simultaneous analysis of free copper(II) and iron(III) in seawater without fear of cross-interference between the solid-state sensors.     

Determination of silver in photographic material by flow-injection analysis with a coated tubular solid-state silver sulphide ion-selective electrode as detector

Summary The incorporation, behaviour and suitability of a simple and cheap home-made coated tubular solid-state silver(I)-selective electrode into the conduits of a flow-injection system is described. With 30 l samples the flow-injection flow-through electrode system covers a working range up to 5000 mg/l. The system is suitable for the determination of silver(I) in diluted plant solutions from photographic material at a sample frequency of about 80 h^–1. This procedure is also characterized by excellent reproducibility (<0.24% for 0.06–76 g/l silver in the original plant solution). The results obtained agree well with results by a standard atomic absorption spectrometric method.

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Bestimmung von Silber in photographischem Material mit Hilfe der Fließinjektionsanalyse mit einer überzogenen Feststoff-Silbersulfid-ionensensitiven Röhren-Elektrode als Detektor

     

Preconcentration of copper on ion-selective imprinted polymer microbeads

Molecular recognition-based separation techniques have received much attention in various fields because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the preparation of such systems. In this study, we have prepared a novel molecular imprinted adsorbent to remove heavy metal ions with high selectivity. The Cu(II)-imprinted poly(ethylene glycol dimethacrylate–methacryloylamidohistidine/Cu(II)) (poly(EGDMA–MAH/Cu(II))) microbeads with an average size of 150–200 μm were prepared by dispersion polymerization. These Cu(II) imprinted microbeads were used in the adsorption–desorption of copper(II) ions from metal solutions. Adsorption equilibria was achieved in about 1 h. The maximum adsorption of Cu(II) ions onto imprinted microbeads was about 48 mg/g. The pH significantly affected the adsorption capacity of imprinted microbeads. The observed adsorption order under competitive conditions was Cu(II) > Zn(II) > Ni(II) > Co(II) in mass basis. The imprinted microbeads can be easily regenerated by 0.1 M EDTA solution with higher effectiveness. The imprinted microbeads showed excellent selectivity for the target molecule (i.e. Cu(II) ions due to molecular geometry). These features make imprinted microbeads very good candidate for selective removal of Cu(II) ions at high adsorption capacity. Detection limit was increased at least 1000-folds with the preconcentration approach using the imprinted microbeads. The method was also applied to certified reference and seawater samples.     

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.