Indirect potentiometric flow-injection determination of silver in photographic fixing solutions

The thiosulfate present in fixing solutions was destroyed on-line by acidification and the undissolved gaseous products were separated from the flow stream by use of polytetrafluoroethylene microporous tubing. The silver was precipitated with an excess of sulfide, and the excess was measured with a silver/silver sulfide electrode. Silver was determined in several ranges from 1 mg 1^?1 to 10 g l^?1.     

Electrochemical determination of norepinephrine on the membrane of silver nanoparticles doped poly-glycine eliminating the interference of ascorbic acid

The silver nanoparticles doped poly-glycine composite membrane was prepared by cyclic voltammetry on the surface of the glassy carbon electrode (GCE). The morphology and electrochemical properties were characterized by scanning electron microscopy and cyclic voltammetry, respectively, and in detail, the electrochemical behaviors of the norepinephrine (NE) on this membrane were studied. The results showed that the membrane had good catalytic properties for the oxidative–reductive reaction of NE. NE had a couple of sensitive oxidative-reductive current peaks. The reductive peak currents were linearly with its concentration in the range of 1.90?×?10^?7 to 7.00?×?10^?6 and 7.00?×?10^?6 to 1.00?×?10^?4?mol l^?1, and the linear regressive equations were i _pc (A)?=?3.73?×?10^?6?+?0.70C (mol l^?1), i _pc (A)?=?9.83?×?10^?5?+?0.12C (mol l^?1), respectively, with the relate coefficient (r) of 0.9926 and 0.9944. The detection limit was 1.2?×?10^?7?mol l^?1 (S/N?=?3), which could be used to determine the content of NE and at the same time, eliminate the interference of the ascorbic acid (AA). The proposed method had high sensitivity, good selectivity and stability.     

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.     

Accumulation and voltammetric measurement of silver at zeolite-containing carbon-paste electrodes

Silver-sensitive chemically modified electrodes are constructed by incorporating zeolites into a conventional carbon-paste mixture. Ion-exchange preconcentration is followed by medium-exchange to an electrolyte solution where the surface-bound silver is measured. The silver response is evaluated with respect to preconcentration time, electrode composition, silver concentration, pH, “cleaning” solution, possible interferences and other variables. Short preconcentration times permit convenient measurements down to the sub-mg l^?1 concentration level. The surface is renewed by placing the electrode in a sodium carbonate solution. For six accumulation/measurement/renewal cycles with a 1 mg l^?1 sample, the relative standard deviation was 3.9%. Similar measurements of mercury are also illustrated.     

Analysis of organic amines and acids for water

Conventional methods for the determination of cyanide in effluents associated with steel-making procedures are compared with a method based on a cyanide-selective electrode. For cyanide levels above 1.0 mg l^-1, the standard argentimetric titration and electrode method give similar results. At lower levels (0.1–1.0 mg l^-1 and 0.01–0.10 mg l^-1), the potentiometric method is compared with pyridine-pyrazolone and pyridine—barbituric acid colorimetric procedures; the pyrazolene method tends to give higher results than the other two methods. Synthetic standards and actual effluent samples are discussed. Problems associated with the determination of cyanide in effluents containing complex iron cyanides and sulphides are examined. Sulphide removal with lead carbonate or cadmium carbonate above pH 11 should not be done until after the distillation.     

Cyanide ion-selective electrodes based on thin electroplated membranes of silver chalcogenides: Part I. Membrane preparation and characterization

Cyanide-responsive ion-selective electrodes have been developed based on thin tellurium-doped silver selenide membranes electrodeposited on platinum substrates. The chemical composition of the electroplated film membranes could be expressed by the general formula Ag_2+δSe_1?xTe_x (where 0.2 < δ < 0.8 and 0.2 ? × ? 0.1). These electrodes exhibit a linear response in cyanide solutions with concentrations ranging from 10^?2 to 10^?6 M, with a slope of the electrode function of about 90 mV (pCN)^?1 (i.e., lower than the theoretically predicted double-Nernstian slope). These electrodes showed very stable behaviour during long-term investigation (several months). The conditions for the electrochemical preparation of cyanide-responsive silver chalcogenide membranes are discussed both from theoretical and practical points of view. X-ray diffraction, energy-dispersive x-ray fluorescence microanalysis (EDAX) and scanning electron microscopy (SEM) were used to examine the membrane composition, structure and surface morphology.     

An iodide/anion exchange route to benzimidazolylidene silver complexes from benzimidazolium iodide: Crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate

Syntheses of N,N′-dibutylbenzimidazolylidene silver complexes having chloride, nitrate or cyanide as an anion part through an iodide/anion exchange from N,N′-dibutylbenzimidazolium iodide are described, representing a practical route to benzimidazolylidene silver complexes from readily accessible benzimidazolium iodide. The crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate have been determined, showing a close ligand-unsupported Ag-Ag interaction in [(NHC)₂]Ag⁺[AgX₂]⁻ and a “T” shape geometry about the silver(I) cation in complexes of chloride, bromide and cyanide, but a nearly linear shape in the bis(N,N′-dibutylbenzimidazolylidene) silver complex [ with non-coordinating nitrate anion.     

The renovated silver ring electrode

In this preliminary note, a new type of working electrode – the renovated silver ring electrode (RSRE) – is presented. The main constituents of the RSRE: a specially constructed silver ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RSRE body. The effectiveness of the renovation procedure was tested by designating the RF and E_pzc and by recording C_d–t curves. As shown on selected examples, RSRE exhibits good performance in underpotential deposition stripping voltammetry (UPD-SV) applied for the determination of Pb(II) traces in certified reference materials.     

Enzymeless determination of cholesterol using gold and silver nanoparticles as electrocatalysts

We present the results of synthesis and study of the electrocatalytic activity of gold and silver nanoparticles of different composition (individual metals, core–shell particles, nanoalloys, and particles synthesized electrochemically), immobilized on the surface of a glassy carbon electrode, with respect to cholesterol. A surfactant (cetyltrimethylammonium bromide) is selected to create an aqueous–organic emulsion of cholesterol. It is demonstrated that nanoparticles with a gold core and a silver shell with the regression equation of I = 1.4 × 10^–5 c _chol + 5.8 × 10^–5 (R ² = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10^–5 c _chol + 3.0 × 10^–4 (R ² = 0.95) possess optimal electrocatalytic characteristics.     

Chemical interactions of pyridine and cyanide with silver

From a quantitative determination of pyridine and cyanide adsorbed on a silver electrode, by a radiochemical technique, we have shown that the two adsorbate - silver systems are different. After a dissolution - redeposition electrochemical cycle the quantity of pyridine adsorbed depends on the charge transfer. For low charge transfer (<50 mC cm^?2) the quantity increases from three to nine monolayers and depends on the nature of the supporting electrolyte, which suggests the formation of new bonds between pyridine, Ag and the anion of the supporting electrolyte. For high charge transfers the quantity of pyridine increases, the rate of increase depending on the supporting electrolyte (KI>KCl>KClO₄); in our opinion this is due to a trapping of pyridine in the salt formed between the support electrolyte anion and silver. The quantity of pyridine adsorbed at the silver electrode which can be as large as 100 equivalent monolayers can explain part of the enhancement of the Raman signal observed for this system.After a dissolution - redeposition electrochemical cycle the quantity of cyanide adsorbed remains constant, the cyanide - silver system is reversible and the Raman enhancement observed at the rest potential, is due only to Ag-CN interactions.     

Normal pulse polarographic quantification of cyanide and sulfide by the anodization of mercury

Normal pulse polarography is used to quantify cyanide and sulfide simultaneously by the anodic oxidation of mercury. The detection limit for cyanide is 18 μg l^-1 by the normal pulse polarographic technique. A supporting electrolyte system of 1 M Na₂CO₃ is optimal with regard to background interferences and sample loss. The electrode reaction for the oxidation of mercury in the presence of cyanide can be described by Hg + pCN^- α Hg(CN)_p^2-p + 2e^-, with p having values of 2, 3 and 4 depending on the surface concentration of cyanide. The feasibility of simultaneous cyanide and sulfide quantification is demonstrated with waste-water samples.     

Flow potentiometric and constant-current stripping analysis for silver(I) with carbon- and platinum-fibre electrodes

At concentrations above 50 μg l^?1, silver(I) is determined in nitric acid medium by means of potentiostatic deposition onto a platinum-fibre electrode and subsequent constant-current stripping in the sample or potentiometric stripping in a potassium permanganate medium. Interference from copper(II) is reduced by a pulsed potential procedure whereby copper deposited onto the fibre electrode is reoxidized intermittently. At concentrations below 50 μg l^?1, silver(I) is determined by using a mercury-coated carbon-fibre electrode and constant-current stripping in acetonitrile containing 0.20 M perchloric acid. Potentiostatic deposition for 30 min yielded a detection limit of 0.24 μg l^?1 silver(I) at the 3σ level.     

Kinetics of silver electrodeposition from thiocarbamide solutions at a regular surface coverage with sulfide ions

Kinetics of silver electrodeposition in the presence of sulfide ions is studied on electrodes renewed by cutting off a thin surface layer, at a controlled time of contact of the “fresh” surface with the electrolyte. Solutions containing 10^?2 M AgNO₃, 0.1 M thiocarbamide, 0.5 M HClO₄, and from 2 × 10^?6 to 1.5 × 10^?5 M Na₂S are studied. It is shown that under the studied conditions, the effect of silver electrodeposition on the surface concentration of sulfide ions is insignificant. As the concentration of sulfide ions in solution and their coverage on the electrode surface θ increase, the cathodic polarization decreases. Tafel curves plotted for θ = const are used in estimating the exchange current i ₀ and the transfer coefficient α. It is shown that α ≈ 0.5 and weakly depends on θ, whereas the exchange current increases with the increase in θ by an approximately linear law from 10^?5 A/cm² at θ ? 0 to 10^?4 A/cm² at θ = 0.43. The obtained data are compared with the results of kinetic studies of silver anodic dissolution in similar solutions.     

Separation and automatic spectrophotometric determination of low concentrations of cyanide in water

Semi-automatic methods are described for the routine determination of cyanide in water. Membrane diffusion and isothermal distillation are examined for the separation/concentration of cyanide; the isothermal distillation procedure is optimized for routine use. An air-segmented flow analyzer is used to quantify cyanide. Two classical spectrophotometric methods are adapted and compared. The method based on reaction with picric acid is applicable at cyanide concentrations exceeding 1 mg l^?1. A modified Aldridge method is far better for lower concentrations. Combination of isothermal distillation with the automatic version of the Aldridge method is suitable for the determination of cyanide in waters in the concentration range 0.01–10 mg l^?1. Interference by sulphide and sulphite and their removal are described.     

Time-resolved surface-enhanced resonance Raman scattering study of the reduction process of heptylviologen monocation radical film on silver electrode surfaces

Time-resolved SERRS spectroscopy was applied to elucidate the mechanism of the reduction process of a heptylviologen monocation radical film to a neutral species on Ag electrode surfaces under various conditions. The film deposited on Ag electrodes at −0.65 V (vs. Ag/AgCl) consists of dimers, (HV^+.)₂. On application of a step potential from −0.65 to −1.2 V, the radical dimer is converted to a neutral species, HV⁰. The time-resolved spectra measured as a function of time after application of the step potential indicates that on the electrode immersed in KBr solutions (0.3 and 3 mol l⁻¹) the radical dimer is at first converted to an intermediate state, which is a surface complex of a monocation radical monomer and a Br⁻ ion (the radical monomer in a type B state), and then reduced to the neutral species. The time-resolved spectra proved also the existence of a disproportionation reaction, i.e. 2HV^+. (type B) → HV²⁺ + HV⁰. The increase in the KBr concentration (0.3 → 3 mol l⁻¹) stabilizes the intermediate surface complex, causing an appreciable decrease in the reduction rate from (HV^+.)₂ to HV⁰. The reduction process on a silver electrode in 0.3 mol l⁻¹ Na₂SO₄ consists of two reaction paths; one is a direct conversion from (HV⁺)₂ to HV⁰ and another is a path through a radical monomer, which gives SERRS features appreciably different from those of type B. The first process proceeds much faster than that on the electrode in the KBr solutions.     

Determination of coenzyme Q10 by in situ EPR spectroelectrochemistry

A rapid and sensitive method is developed for the determination of coenzyme Q₁₀ (CoQ₁₀) on the basis of the measurement of the radical intermediate (ubisemiquinone) formed during the reduction reaction of CoQ₁₀ at a silver electrode by in situ EPR spectroelectrochemical techniques. At the potential of −0.55 V (versus SCE), the ubisemiquinone is formed and is stable in ethanol+water. Under optimal conditions, it was found that the proposed method provided a linear response over the CoQ₁₀ concentration range 5–100 μmol l⁻¹ with a detection limit of 3 μmol l⁻¹. The relative standard deviation of the results was 7.5% for six successive determinations at 10 μmol l⁻¹ CoQ₁₀. This method is a useful tool for improving the selectivity when other chemicals present in the sample do not interfere in the assay.     

Carbon paste electrode modified with silver thimerosal for the potentiometric flow injection analysis of silver(I)

The utility of carbon paste electrode modified with silver ethylmercurythiosalicylate (silver thimerosal) in both static mode and flow injection analysis (FIA) is demonstrated. The electrode was fully characterized in terms of composition, response time, thermal stability, usable pH and ionic strength ranges. It has been shown that diisononyl phthalate (DINP) acts as more suitable solvent mediator for preparation of the electrode, which exhibits linear response range to Ag(I) extending from 5.0 × 10⁻⁷ to 1.0 × 10⁻³ M with detection limit of 2.5 × 10⁻⁷ M and Nernstian slope of 59.3 ± 1.0 mV/decade. The proposed chemically modified carbon paste electrode shows a very good selectivity for Ag(I) over a wide variety of metal ions and successfully used for the determination of the silver content of silver sulphadiazine (burning cream) and developed radiological films. The electrode was also used as an indicator electrode in the potentiometric titration of thiopental and thimerosal with AgNO₃.     

Determination of trace amounts of silver with a chemically modified carbon paste electrode

A method for the determination of trace amounts of silver with a chemically modified carbon paste electrode is described. The modified electrode is prepared by simply mixing a chelating resin (a polythioether backbone and dioxymonosulphur polyethylene polyimines in the side-chain polymer) with graphite powder and Nujol oil. By immersing the electrode in a silver sample solution (pH = 6.5–7.5), silver can be adsorbed on the electrode surface and then determined by voltammetry in a separate blank solution. The response depends on the concentration of silver and the preconcentration time. For a preconcentration time of 5 min, the detection limit is about 3 × 10^?10 M and the linear range is from 5 × 10^?10 to 1 × 10^?7 M with a relative standard deviation of 4%. Many common metal ions have no or little effect on the determination of silver. The recommended procedure was applied to the determination of trace amounts of silver in waste water.     

A new generation of cyanide ion-selective membranes for flow injection application: part II. Comparative study of cyanide flow-injection detectors based on thin electroplated silver chalcogenide membranes

Using induced cathodic electrodeposition a number of silver chalcogenide thin layer membranes of non-trivial composition have been synthesized and their performance as ion-selective flow-injection potentiometric detectors (FIPDs) for free cyanide has been critically estimated in the context of the stringent requirements for toxic cyanide environmental monitoring. AgSCN/Ag₂S, Ag₂S, Ag_2+δSe, Ag_2+δSe_1−xTe_x (0 < δ < 0.25 and x ≈ 0.13), Ag₂Se and Ag₂Se_1−xTe_x electroplated membranes were selected for the present performance-based comparative study in order to obtain a feedback information about the effect of membrane composition. Both silver selenide and Te-doped silver selenide membranes, irrespective of their stoichiometry with respect to silver, exhibit the lowest detection limit for CN⁻ (52 ppb) with linear double-Nernstian response down to 130 ppb. The type of chalcogene anion in the membrane composition proves to exert dominant effect on the general performance characteristics of the newly developed FIPDs. The silver stoichiometry (intrinsic defects factor) and the inclusion of Te-dopant (extrinsic defects factor) have more pronounced effect on the profile of the output signal and exert moderate control on the detectors selectivity and baseline stability. This new generation of CN⁻—ion-selective membranes for FIPDs exhibits high selectivity against the common interferents present in cyanide effluents such as SCN⁻, S₂O₃²⁻, Cl⁻ and do not get poisoned in the presence of S²⁻. Moreover, their long-term stability and signal reproducibility, which make redundant the regular day-to-day calibration, coupled with the cost-effective technology for membranes preparation and easy re-generation make them attractive candidates for incorporation into automated in-field devices for in situ cyanide toxic species monitoring.     

Kinetics of silver dissolution in sulfide containing thiocarbamide electrolytes

Effective values of reaction order with respect to ligand P, transfer coefficient α, and exchange current i ₀ at constant silver surface coverages θ by sulfide ions are measured. The employed solutions contained from 0.4 to 0.05 M thiocarbamide, 0.5 M HClO₄, 10^?4 M AgNO₃, and from 10^?5 to 10^?4 M Na₂S. It is shown that the exchange current grows approximately linearly from 10^?5 to 1.5 × 10^?4 A/cm² at θ increase in the range from zero to 0.8, while α and P values grow negligibly in the ranges of 0.4–0.45 and 0.9–1.1, accordingly. The obtained results are compared with the data of similar studies of the gold behavior in acidic thiocarbamide solutions. The possible reasons for the different effects of sulfide ion chemisorption on the anodic dissolution of gold and silver in the studied solutions are discussed.