Thermodynamics of silver—silver halide electrodes and thermodynamic solubility products of silver halides in glycerol + water mixtures at different temperatures

The standard potentials of silver—silver bromide and silver—silver iodide electrodes in glycerol+water mixtures containing 5, 10, 20 and 30 wt% glycerol were determined from electromotive force measurements of the cell Ag(s), AgX(s), KX(c)//KCl(c), AgCl(s), Ag(s), where X is Br or I, at seven different temperatures in the range 5–35°C. The standard potentials in each solvent are represented as a function of temperature. The standard thermodynamic functions for the electrode reactions, the primary medium effects of various solvents upon X⁻, and the standard thermodynamic quantities for the transfer of 1 g-ion of X⁻ from water to the respective glycerol + water media are evaluated and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents. From the values of the Ag/Ag⁺ and Ag/AgX, X⁻ electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide and silver iodide have been determined in glycerol + water solvent mixtures at different temperatures.     

Potentiometric detection of halides and pseudohalides in anion chromatography

A small piece of silver wire, coated with an insoluble silver salt, can be used as a selective potentiometric detector for halides in ion chromatography. Several coated electrodes were examined by electron microscopy and their response to various anions evaluated in a flow-injection system. A silver/silver chloride was found to be a selective and reproducible detector for chloride, bromide, iodide, thiocyanate and thiosulfate separated by ion chromatography. Calibration curves were non-linear and had slopes ranging from 40 to 60 mV per concentration decade in the range 0.1–2 mM. A working range of 0.05–2 mM was used. This electrode is also satisfactory when gradient elution is used in ion chromatography.     

Synthesis of silver nanowires and their applications in the electrochemical detection of halide

A silver nanowires modified platinum (Ag NWs/Pt) electrode was developed for simultaneous and selective determination of chloride, bromide and iodide ions by cyclic voltammetry in aqueous solutions. Silver nanowires were synthesized by an l-cysteine-assisted poly (vinyl pyrrolidone) (PVP)-mediated polyol route. X-ray diffraction (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the prepared nanowires. The intrinsic high surface area and the fast electron transfer rate ascribed from the nanowire structure could further improve halide detection performance. The determination was based on measurement of the well-separated oxidation peak currents of respective silver halides formed on the surface of silver during an anodic potential sweep. The concentration range was linear from 50 μM to 20.2 mM for bromide and iodide and 200 μM to 20.2 mM for chloride, and the sensitivity was 0.059 μA/mM, 0.042 μA/mM and 0.032 μA/mM for chloride, bromide and iodide, respectively. The correlation coefficient was 0.999 in each case. The Ag NWs/Pt electrode offered a useful platform for the development of a highly sensitive halide sensor.     

Anionic interferences with copper ion-selective electrodes chloride and bromide interferences

The effect ofhalide ions on copper ion-selective electrodes is connected with complexation and redox reactions, with the formation of amorphous sulphur, which by blocking the surface causes instability of potential response. It may be eliminated by addition of sodium thiosulphate solution. The electrode behaviour has been explained on the basis of the diffusion model. An equation is proposed for linearization of the calibration curve. The parameters of the semiempirical model which describes the electrode behaviour agree well with the physical meaning presented by the diffusion model. The treatment given enables analytical measurements of copper concentration to be made even in the presence of significant concentrations of chloride or bromide.     

Ion-selective carbon-paste electrodes for halides and silver(I) ions

The behaviour of a simple type of ion-selective electrode for halogens and silver has been studied. The electrode consists of a plastic body filled with carbon paste, the surface of which can be easily renewed. The paste composition is based on carbon-nujol (5:1, w/v) or carbon-paraffin wax (3:1,w/w) containing a prepared mixture of silver halide-silver sulphide (1–30%). The electrodes have low ohmic resistance and show a rapid Nernstian response (within 2–5 mV) for halide and silver ions down to 5·10^-5M chloride, 1·10^-5M bromide and 5·10^-7M iodide with the respective electrodes. Ions forming very stable complexes with halide or silver and those having strong oxidizing or reducing action interfere.     

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.     

Ion-selective chalcogenide electrodes for a number of cations

Ion-selective chalcogenide disc electrodes have been developed which are responsive to cations such as silver, lead, chromium(III), nickel, cobalt(II), cadmium, zinc, copper(II) and manganese(II) ions. Each was prepared by using the corresponding metal chalcogenide with silver sulphide. An electrode was assembled with both a compacted and a sintered disc. The sintered electrodes were more sensitive and stable than the compacted ones. Response to silver ion was 59.5 mV pAg , to lead, nickel, cadmium, zinc and copper(II) 29.5 mV pM and to chromium(III) 20 mV pM . Cobalt(II) and manganese(II) electrodes had a non-Nernstian response of 25 mV pM . Both selenides and tellurides can be used for potentiometric determination, but the manganese(II) electrode serves as an analytical tool only when the disc consists of manganese(II) telluride and silver sulphide.     

Vergleich der Eigenschaften von elektrolytisch hergestellten und von handelsüblichen Halogenidelektroden

The preparation of chloride, bromide and iodide electrodes by electrolytical coating of silver rods has been described. These electrodes show at least as good characteristics as commercially available halide electrodes. Main advantages of the coated types are simple preparation, mechanical robustness and easy regeneration. Due to the lack of any cemented areas or electrical contact points, the use of these electrodes is mostly free from interferences.     

Anodic behaviour of a dropping lead amalgam electrode in halide medium in the presence of EDTA

The behaviour of the dropping lead amalgam electrode has been studied. Calculated and experimental current-voltage curves have been compared and an explanation has been given for the observed differences. Selective determination of metal ions appears to be possible in the presence of saturated chloride, 1M bromide and 10(-2)M iodide by means of amperometric complex-formation titrations using normal pulse polarography with the dropping lead amalgam electrode.     

Edge Plane Pyrolytic Graphite Electrodes for Halide Detection in Aqueous Solutions

The behavior of chloride, bromide and iodide at edge plane pyrolytic graphite electrodes has been explored in aqueous acid solutions. The voltammetric response in each case has been compared with that of basal plane pyrolytic graphite, glassy carbon and boron‐doped diamond. The electrochemical oxidation of chloride is found to only occur on boron‐doped diamond while the electrochemical reversibility for the oxidation of bromide on edge plane pyrolytic graphite is similar to that seen at glassy carbon whilst being superior to basal plane pyrolytic graphite and boron‐doped diamond. In the case of iodide oxidation, edge plane and basal plane pyrolytic graphite and glassy carbon display similar electrode kinetics but are all superior to boron‐doped diamond. The analytical possibilities were examined using the edge plane pyrolytic graphite electrode for both iodide and bromine where is was found that, based on cyclic voltammetry, detection limits in the order of 10^?6 M are possible.     

Flow-injection system with ion-exchange separation and potentiometric detection for the determination of three halides

The use of ion exchangers in flow-injection systems is reviewed briefly. In the method described, halides are separated on a short column of a strongly basic ion-exchange resin (Dowex 1-X8) placed in the flow-injection conduit, with a laboratory-made tubular silver/silver halide ion-selective electrode as potentiometric sensor. The response capabilities of the different halide-selective electrodes to a wide concentration range (20-5000 mg dm^?3) of single and mixed halide solutions with and without the incorporated ion-exchange column are compared. By careful selection of suitable concentrations of the potassium nitrate carrier/eluent stream to satisfy the requirements of both the ion-exchange column and the halide-selective electrode, it is possible to separate and determine chloride, bromide and iodide in mixed halide solutions with a detection limit of 5 mg dm^?3. The bromide-selective electrode is the most satisfactory detector.     

Titrations using an apparatus for recording the antilogarithm of pH or pM

A titration apparatus plotting either the concentration of sample ion or the concentration of titrant ion has been tested. An antilog apparatus, converting measured e.m.f. values into concentrations is connected to ordinary titration equipment. The instrument has been tested by means of acid—base titrations (titrations of mixtures of weak acids and of a weak and a strong acid), precipitation titrations (determination of the chloride concentration in tap-water, titration of mixtures of halides), titrations with ion-selective electrodes (determination of the fluoride content of toothpaste) and complexometric titrations (determination of copper with EDTA, using mercuric ion as indicator ion and amalgamated silver rod as indicator electrode, or using a copper-selective indicator electrode). The method considerably simplifies the evaluation of the results as compared to conventional potentiometric titrations.     

An XPS investigation of silver bromide-coated ion-selective electrodes

XPS data of AgBr-coated ion-selective electrodes exposed to high concentrations of Ag⁺, Cl⁻, Br⁻, I⁻, and NH₃ revealed a change in the surface properties of the original electrode. A 40 min to one week exposure of the silver bromide ion-selective electrode surface to solutions containing high concentrations of chloride ions leads to the formation of a mixed halide layer, as the chloride ions are incorporated in the surface. Exposure to high concentrations of iodide-containing solutions results in a new silver iodide layer on top of the original silver bromide laver. Silver ions diffuse to the newly formed layers. NH₃ results in the rapid degradation of the AgBr surface as the diamine complex, Ag(NH₃)⁺₂, is formed.     

Highly sensitive determination of iodide by ion chromatography with amperometric detection at a silver-based carbon paste electrode

A silver-based solid carbon paste electrode was developed for use as a detector in ion chromatography (IC) for the sensitive determination of iodide in real samples. Micro- and nano-particles of silver were investigated for the fabrication of different electrodes. The iodide assay was based on IC with amperometric detection (IC-AD) at a silver composite electrode polarized at +0.080 V versus Ag/AgCl. Free iodide and organoiodide compounds were studied. The detection process was characterized by studying the redox behavior of iodide ions at both silver and silver composite electrodes by cyclic voltammetry (CV). The presence of iodide ions in solution was found to considerably facilitate metallic silver oxidation, with response currents directly related to iodide concentration. The calibration curve at the selected silver carbon paste electrode was linear in the concentration range comprised between 0.635 microg/L and 63.5 microg/L iodide. The relative standard deviation (R.S.D.) for successive injections was below 3% for all iodide standard solutions investigated. The limit of detection (LOD) was 0.47 microg/L (3.7 nmol/L) for an injection volume of 20 microL, i.e. 74 fmol injected. The IC-AD method was successfully applied to the determination of iodide in complex real samples such as table salts, sea products and iodide bound drug compounds. The analytical accuracy was verified by the assay of iodide in milk powder from an iodide certified reference material (CRM) Community Bureau of Reference (BCR) 150.     

The response of halide ion-selective electrodes to redox systems : A comparison between silver/silver halide electrodes and silver sulphide- based halide ion-selective electrodes

Silver/silver chloride and bromide electrodes, prepared by anodizing ordinary silver electrodes, and the corresponding ion-selective electrodes based on silver sulphide, were tested for their susceptibility towards redox systems. It proved that the latter type of electrode responded significantly to strong oxidants. In contrast, the silver/silver halide types were highly resistant to redox interference provided that the silver halide layer was free from open pores. This could be achieved by generation of sufficiently thick layers and by selection of suitable current densities during electrodeposition (<20 mA cm^-2). The interrelation between the conditions of silver chloride film generation and redox resistance of the resulting electrodes is described in detail.     

Thermodynamic properties of the silver ion in alcohol + water solvent mixtures from electromotive force measurements and thermodynamic solubility product constants of AgX (X = Cl,Br, I or CNS) at different temperatures

The standard potentials of the silver-silver ion electrode in alcohol+water solvent mixtures containing 10 and 20 wt% methanol, ethanol, 1-propanol and 2-propanol have been determined from the electromotive force measurements of the cell Ag(s), AgCl(s), NaCl(c), NaNO₃(c)// NaNO₃(c), AgNO₃(c), Ag(s) at seven different temperatures in the range 5–35°C. The standard potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the electrode reaction, the primary medium effects of various solvents upon Ag⁺, and the standard thermodynamic quantities for the transfer of 1 g-ion of Ag⁺ from water to the respective alcohol + water media have been evaluated and discussed in the light of ion-solvent interactions as well as the structural changes of the solvents. From the values of the standard potentials of the Ag/Ag⁺ and Ag/AgX, X^? electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide, silver iodide and silver thiocyanate have been determined in alcohol + water solvent mixtures at different temperatures.     

Using ratiometric indicator-displacement assays in semi-quantitative colorimetric determination of chloride, bromide, and iodide anions

A ratiometric indicator-displacement assay (RIDA) array has been developed for the semi-quantitative colorimetric determination of chloride, bromide, and iodide anions. Determinations of these halide anions follow the displacement reaction using the chelate compound of (2-(3,5-dibromo-2-pyridylazo)-5-(diethylamino)phenol) (3,5-Br2-PADAP) and heavy metal salts as colorimetric reagent. Different from regular silver nitrate titrations, the chloride, bromide, and iodide anions compete with the 3,5-Br2-PADAP ligand and change the colour of the 3,5-Br2-PADAP-metal chelate compound dramatically. These clearer colour changes make the semi-quantitative colorimetric determination of chloride, bromide, and iodide anions possible. The colour changes are imaged using a conventional flatbed scanner, and digitized. After statistical analysis, these colour changes in the RIDA array provide facile identification of chloride, bromide, and iodide anions at a wide concentration range (10 μM to 10 mM) without any misclassification. The RIDA array is able to discriminate without misclassifications among seven concentrations of chloride, bromide, and iodide anions. No shelf life issue exists because the chelating compounds react with halide anions directly without any pre-immobilizations.     

Determination of the Selectivity of Electrodes Made of a Mixture of Nonstoichiometric Silver and Copper(I) Sulfides in the Analysis of Sulfur-Containing Aqueous Solutions

The possibility of using electrodes made of a mixture of nonstoichiometric silver and copper(I) sulfides in the analysis of sulfur-containing aqueous solutions by direct potentiometry and potentiometric titration was assessed. The selectivity coefficients of the electrodes under study to chloride and iodide ions were determined. The effect of pH on the performance and conductivity of electrodes was studied.     

Study of the potential response of solid-state chloride electrodes at low concentration ranges

Ion-selective electrodes based on silver chloride precipitates have been investigated in the low concentration range, by use of a specially designed cell of small volume. Electrode potential measurements and silver determinations in the corresponding solutions by atomic-absorption spectrometry were made. The results prove that the potential response of these ion-selective electrodes in the low concentration ranges is governed by inequality of the ion concentrations in the boundary zone of the test solution contacting the electrode membrane. This is a result of adsorption-desorption processes, a dissolution process followed by recrystallization of the silver chloride at the electrode membrane surface, and photoreduction of silver ions at the electrode surface.     

Liquid-phase microextraction-gas chromatography-mass spectrometry for the determination of bromate, iodate, bromide and iodide in high-chloride matrix

In the determination of bromate and iodate, any free bromide and iodide present was quantitatively removed by anion exchange with silver chloride exploiting the differences in silver salts solubility product, being AgCl, 1.8 x 10(-10), AgBr, 5.0 x 10(-13), AgI, 8.3 x 10(-17), AgBrO(3), 5.5 x 10(-5) and AgIO(3), 3.1 x 10(-8). The oxyhalides were reduced with ascorbic acid to halides and converted to 4-bromo-2,6-dimethylaniline and 4-iodo-2,6-dimethylaniline by their reaction with 2-iodosobenzoate in the presence of 2,6-dimethylaniline at pH 6.4 and 2-3, respectively. Single drop microextraction (SDME) of the haloanilines in 2 microl of toluene and injection of the whole extract into GC-MS, or liquid-phase microextraction (LPME) into 50 microl of toluene and injection of 2 microl of extract, resulted in a sensitive method for bromate and iodate. The latter method of extraction has been found more robust, sensitive and to give better extraction in shorter period than SDME. Total bromine/iodine was determined without any treatment with silver chloride. High concentration of chloride in the matrix did not interfere. A rectilinear calibration graph was obtained for 0.05 microg-25 mg l(-1) of bromate/bromide and iodate/iodide, the limit of detection were 20 ng l(-1) of bromate, 15 ng l(-1) of iodate, 20 ng l(-1) of bromide and 10 ng l(-1) of iodide (by LPME in 50 microl of toluene). The method has been applied to seawater and table salt. From the pooled data, the average recovery of spiked oxyhalide/halide to real samples was in range 96.7-105.7% with RSD in range 1.6-6.5%.