Studies of copper(II) sulphide ion-selective electrodes

Changes in liquid junction potentials in copper(II) solutions were measured when different reference electrodes were used. The slope and intercept of a calibration curve for a copper-selective electrode will depend on the selection of reference electrode. The condition of the electrode surface of an Orion copper-selective electrode was studied microscopically and the influence of redox potential on stability of the electrode against corrosion is discussed. Oxidizing solutions will produce pits at dislocations in the material and there will be a mixed electrode potential. The slope, stability, and speed of response are much lower when the surface contains pits. Diamond-polishing was shown to improve the electrode significantly.     

Mercury(II) ion-selective electrodes based on heterocyclic systems

Mercury ion-selective electrodes (ISEs) were prepared with a polymeric membrane based on heterocyclic systems: 2-methylsulfanyl-4-(4-nitro-phenyl)-l-p-tolyl-1H-imidazole (I) and 2,4-diphenyl-l-p-tolyl-1H-imidazole (II) as the ionophores. Several ISEs were conditioned and tested for the selection of common ions. The electrodes based on these ionophores showed a good potentiometric response for Hg2+ ions over a wide concentration range of 5.0 x 10(5-) - 1.0 x 10(-1)M with near-Nernstian slopes. Stable potentiometric signals were obtained within a short time period of 20 s. The detection limits, the working pH range of the electrodes were 1.0 x 10(-5) M and 1.6-4.4 respectively. The electrodes showed better selectivity for Hg2+ ions over many of the alkali, alkaline-earth and heavy metal ions. Also sharp end points were obtained when these sensors were used as indicator electrodes for the potentiometric titration of Hg2+ ions with iodide ions.     

Lead(II) and copper(II) ion-selective electrodes based on two heterocyclic compounds

In this paper, two nitrogen, sulphur or oxygen containing heterocyclic compounds were used as ionophores in ion-selective electrodes. In these two ion-selective electrodes, 2,6-di(5-methyl-1,3,4-oxadiazol-5-yl)pyridine (DMOP) gives the best Pb²⁺ sensitivity and 2,5-di(2′-methylpyridinethio)thiadiazole (DPTD) gives the best sensitivity for Cu²⁺. These electrodes are composed of KTpClPB as anion excluder and DOS as plasticizer. The two membrane electrodes show Nernstian or near-Nernstian response towards Pb²⁺ or Cu²⁺ (29.3 and 27.3 mV/decade, respectively) over the concentration range 10⁻⁵∼10⁻² and 10⁻⁶∼10⁻³ M, respectively. The response time was less than 20 sec and a good reproducibility over a period of 2 months was observed. The electrodes exhibited good selectivities over a number of alkali, alkaline earth and transition metal ions. The proposed electrodes have also been used for the direct determination of Pb²⁺ and Cu²⁺ ions in real samples.     

Solid-state ion-selective electrodes for the potentiometric determination of hexacyanoferrate (II)

Hexacyanoferrate(II)-sensing electrodes were prepared by mixing Ag₂S and Ag₄Fe (CN)₆. The 6:1 Ag₂S/Ag₄Fe (CN)₆ provided the best potentiometric response and speed of response. The log concentration vs. potential curves were linear with Nernstian slope (14.8 mV/decade) over the range 10^?1-10^?6 M hexacyanoferrate (II) at pH 7.00 with constant ionic strength. Interferences included iodide, sulfide and bromide. This electrode was used as indicator in potentiometric titrations of hexacyanoferrate (II).     

Comparison of copper(II) ion-selective electrodes for measurements at micromolar concentrations

Four types of copper ion-selective electrodes have been tested for determining copper at concentrations below lO^-6 mol 1^l-1. None of the electrodes has a Nemstian response in dilute copper solutions in this concentration range, though their responses are linear in pCu buffer solutions. The causes of the deviations are a direct redox effect in the case of an electrode with a Cu_1.8,Se single crystal membrane, production of copper ions by oxidation of the membrane itself in Ag₂S—CuS membrane electrodes, and a combination of the two in the case of the R??i?ka Selectrode. The electrode potentials are affected by the oxygen content and pH of the sample solution and the condition of the membrane surface. Precision tests on two types of electrode are described.     

Poly(n-butyl acrylate) based lead (II) selective electrodes

Poly(n-butyl acrylate) membranes for potentiometric ion-selective electrodes were developed and studied on example of lead-selective sensors. A novel approach resulting in Nernstian responses of tested sensor was proposed. Introduction of 5% (w/w) hydroxyethyl methacrylate into n-butyl acrylate moiety resulted in significant improvement of sensor analytical parameters. For the latter membrane material linear responses were obtained within lead activities range from 10⁻² to 10⁻⁹ mol/dm³, while for poly(n-butyl acrylate) based membranes pretreated in the same manner super-Nernstian behavior was obtained in a parallel experiment. Electrochemical impedance spectroscopy studies did not reveal significant differences between these two membranes, also similar lead ions diffusion coefficients were determined using inductively coupled plasma mass spectrometry with laser ablation.The difference between two kinds of membranes was found to concern higher Pb(II) ions contents in the surface part of the membrane with hydroxyethyl methacrylate, resulting in balanced Pb ions fluxes from/to the membrane.     

Formation constants for Pb(II)-iminodiacetic acid complexes as determined by potentiometry with glass,Pb-Amalgam and lead ion-selective electrodes

The complex formation between Pb(II) and iminodiacetic acid was studied at 25°C in 1 mol dm⁻³ KNO₃ medium. The e.m.f. measurements were carried out by means of glass, Pb-amalgam and lead ion-selective electrodes. Three species PbHL⁺, PbL and PbL_staggered2²⁻ were found in the −log[H⁺] region 2–9. The protonation constants of iminodiacetic acid and the formation constants of the complexes are tabulated in Tables 1 and 2, respectively. By comparison of the results from the amalgam electrode and ion-selective electrode systems, it was found that the ion-selective electrode shows a satisfactory performance in the solutions examined.     

An evaluation of some commercial lead(II)-selective electrodes

Two types of commercial lead(II)-selective electrode, the Orion 94-82 and the R??i?ka lead Selectrode, are compared. Calibration curves were determined in both buffered and unbuffered lead-ion solutions repeatedly for several weeks. Selectivities with respect to copper(II), silver(I), mercury(II), iron(III), zinc and cadmium were examined as well as the pH response by the mixed solution method. The response times of the electrodes were also studied.     

Coated-wire ion-selective electrodes

Coated-wire ion-selective electrodes were first developed in 1971, and comprise a film of polyvinyl chloride or other suitable polymeric matrix substrate containing a dissolved electroactive species, coated on a conducting substrate (generally a metal, although any material with conductivity substantially higher than that of the film can be used). Electrodes of this sort are simple, inexpensive, durable and capable of reliable response in the concentration range of 10^?1 to 10^?6 M for a wide variety of both organic and inorganic cations and anions. The principles on which these electrodes are based, as well as their application to a variety of analytical problems, will be discussed.     

Neutral-carrier-based ion-selective electrodes

Neutral-carrier-based ion-selective electrodes for the assay of alkali and alkaline earth metal cations have advanced to become the most frequently used potentiometric sensors in clinical chemistry. The major developments since the realization of the first potentiometric cell assemblies utilizing electrically neutral complexing agents (valinomycin and the macrotetrolides) in 1966 are presented.     

New cesium ion-selective electrodes based on anilino-(1,3-dioxo-2-indanylidene) acetonitrile derivatives

Cesium ion-selective PVC membrane electrodes based on anilino-(1,3-dioxo-2-indanylidene) acetonitrile derivatives as a novel class of neutral ionophores were examined. The ionophores were p-methoxyanilino-(1,3-dioxo-2-indanylidene) acetonitrile, p-methylanilino-(1,3-dioxo-2-indanylidene) acetonitrile and p-N,N-dimethylanilino-(1,3-dioxo-2-indanylidene) acetonitrile. The anilino-(1,3-dioxo-2-indanylidene) acetonitrile proved to work well with cesium, the corresponding electrodes display a response to this ion. The most favourable ionophore was p-methoxyanilino-(1,3-dioxo-2-indanylidene) acetonitrile, especially when the secondary ion exchanger potassium tetrakis (4-chlorophenyl) borate was incorporated in 2-nitrophenyl octyl ether for ion-selective electrode membrane construction. The response function was linear within the concentration range 10(-1)-2.5x10(-5) mol l(-1) and the slope was 52 mV decade(-1). The detection limit remained at 6.3x10(-6) mol(-1). The selectivity and response time of the electrode was studied and it was found that the electrode exhibited good selectivity for cesium over alkali, alkaline earth and some transition metal ions. The electrode response was stable over a wide pH range. The lifetime of the electrode was about 1 month.     

Copper(II) ion-selective microelectrochemical transistor

A device has been developed for the measurement of copper(II) ions (Cu⁺⁺) in aqueous medium. The device reported here is an electrochemical transistor that consists of two platinum electrodes separated by 100-μm spacing and bridged with an anodically grown polycarbazole film. The undoped polycarbazole film is observed to be highly selective for the Cu(II) ions. In a completed device, the conductivity of the polycarbazole film changes on addition of Cu (II)ions. This change in conductivity is attributed to the conformational changes in the polymer phase on occupation of the Cu(II) ions, without affecting electron/proton transfer. The device turns on by adding 2.5×10⁻⁶ M Cu(II) ions and reaches a saturation region above a concentration of 10⁻⁴ M Cu(II) ions. In this concentration range, the plot of I _D vs log[Cu(II)] is linear. The selectivity of the device for other metal ions such as Cu(I), Co(II), Fe(II), Fe(III), Zn(II), and Pb(II) is also studied.     

Copper(II) ion-selective microelectrochemical transistor

A device has been developed for the measurement of copper(II) ions (Cu²⁺) in aqueous medium. The device reported here is an electrochemical transistor which consists of two platinum electrodes separated by 100 μm spacing and bridged with an anodically grown film of polycarbazole. Polycarbazole film (undoped form) is observed to be highly selective for the Cu(II) ions. In a completed device, the conductivity of the polycarbazole film changes on addition of Cu(II) ions. The change in conductivity is attributed to the conformational changes in the polymer phase on occupation of the Cu(II) ions, without affecting electron/proton transfer. The device turns on by adding 2.5 × 10⁻⁶ M Cu(II) ions and reaches a saturation region beyond 10⁻⁴ M Cu(II) ion concentrations. In the above concentration range, the device response [I _D vs. log Cu(II) ion concentration] is linear. The selectivity of the device for other metal ions such as Cu(I), Ni(II), Co(II), Fe(II), Fe(III), Zn(II) and Pb(II) is also studied. Received: 6 April 1999 / Accepted: 20 August 1999     

Potentiometric microdetermination of lead(II) with an ion-selective lead electrode and its application to the analysis of organic lead compounds

Summary A method for the microdetermination of lead(II) by direct potentiometric titration with 0.0025 M sodium molybdate is described. A lead-selective indicator electrode and a double-junction reference electrode are used in conjunction with an expanded-scale pH-meter to detect the end-point. If the titrant is standardized against 1.5 mg of lead(II), accurate results are obtained for 1–2 mg of lead: the absolute error does not exceed 3gmg of lead. The relative standard deviation is 0.05%. The optimum pH for the titration is 5–5.5. In water-organic solvent mixtures the potential break at the endpoint increases, but the electrode response becomes very slow. The titration of lead is also possible in sodium nitrate and/or perchlorate media, so this titration is applicable to the microdetermination of lead in organic lead compounds after wet mineralization with HNO₃ and/or HClO₄. Chloride (up to 1000 times the lead content) and bromide (100 times) do not interfere. Iodide and sulphate interfere. Five organic lead compounds have been analysed successfully: the standard deviation of the absolute error was 0.1%.

---

Zusammenfassung Ein Verfahren zur Mikrobestimmung von Blei(II) durch direkte potentiometrische Titration mit 0,0025M Natriummolybdat wurde beschrieben. Eine bleiempfindliche Indikatorelektrode und eine Bezugselektrode mit KNO₃-Zwischenelektrolyt wurde in Kombination mit einem pH-Meter mit gedehnter Skala zur Erkennung des Titrationsendpunktes verwendet. Unter Standardisierung der Maßlösung gegen 1,5 mg Blei(II) werden genaue Resultate im Bereich von 1 bis 2 mg Blei erhalten: der absolute Fehler ist innerhalb ±3g Blei. Die relative Standardabweichung beträgt 0,05%. Das günstigste pH liegt im Bereich 5–5,5. In Wasser-Aceton oder -Methanol nimmt der Potentialsprung am Äquivalenzpunkt stark zu; gleichzeitig wird jedoch das Ansprechen der Elektroden sehr langsam. Die Titration von Blei ist möglich auch in Medien von Natriumnitrat oder/und Natriumperchlorat, was die Anwendung dieser Titration auf die Bleimikrobestimmung in bleihaltigen organischen Verbindungen nach Mineralisierung auf nassem Wege mit HNO₃ oder/und HClO₄ ermöglicht. Chlorid (bis zum 1000fachen Gehalt an Blei) und Bromid (100fache Menge) stören nicht. Iodid und Sulfat stören. Fünf bleihaltige organische Verbindungen wurden erfolgreich analysiert; die Standardabweichung des absoluten Fehlers betrug 0,1%.

     

Continuous flow analysis of lead (II) and mercury (II) with substituted diazacrown ionophore membrane electrodes

A novel flow cell for use with ion-selective membrane electrodes is reported in which the carrier stream is drawn through a tube that suppresses the pump noise. PVC membrane electrodes based on 7,16-dithenoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTODC), and 7,16-di-(2-thiopheneacetyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTAODC) for lead (II), and 7,16-dithenyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTDC) and 7,16-di-(2-methylquinolyl)-1,4,10,13-tertraoxa-7,16-diazacyclootadecane (DQDC), for mercury (II) were prepared and evaluated. The linear ranges were pPb: 5.5-3.0 (DTODC) and 6.0-2.0 (DTAODC); pHg: 5.5-3.0 (DTDC) and 4.5-2.5 (DQDC). With flow rate of 3 ml min(-1) the repeatability of measurements was less than 5% RSD (n = 3). The system was applied to the determination of lead (II) and mercury (II) in spiked natural water samples.     

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.     

New lead(II) catecholate and o-semiquinone complexes

Lead(II) catecholate complexes were prepared by reduction of 3,6-di-tert-butyl-o-benzoquinone and its derivatives with lead metal in THF. The molecular structure of the (CatPb)₄·(PbO)₂·6C₃H₆O complex (Cat is the dianion of 3,6-di-tert-butylcatechol), which was synthesized by hydrolysis of lead 3,6-di-tert-butylcatecholate in acetone, was established by X-ray diffraction. A series of lead(II) o-semiquinone complexes, which were prepared by the addition of the phenoxyl radical to lead catecholates or by oxidation of the latter with mercury(II), copper(II), or silver(I) halides, were studied by the ESR method. Lead(II) mono-o-semiquinolate complexes undergo symmetrization to form stable bis-o-semiquinolates, which were isolated and characterized in individual state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1103–1111, July, 2006.     

Screen-printed copper ion-selective electrodes

A simple, low-cost and reproducible method for the mass production of potentiometric ion-selective electrodes for copper ions is presented. These planar, strip sensors were obtained by screen-printing. The application of pastes cured at low temperature allows printing of the sensors on low-cost, plastic substrates. The pastes for printing of ion-sensitive thick-film membranes were based on copper (1) and copper (II) sulfides. The analytical characteristics of the thick-film electrodes were compared. The analytical properties (range of determination, sensitivity, selectivity, response time) of the copper (I) sulfide-based sensors were comparable with those for conventional ion-selective electrodes.