Needle-type ultra micro silver/silver chloride reference electrode for use in micro-electrochemistry.

A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 microm and 0.5 +/- 0.2 microm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a micro-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5-9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.     

Improvement of the silver/silver chloride reference electrode and its application to pH measurement

When a silver/silver chloride (Ag AgCl ) reference electrode was used continuously in a low conductivity solution or reductive solution, it was often observed that stability of the liquid junction potential was lost. This phenomenon was remarkable with a Ag AgCl reference electrode compared to a calomel reference electrode. We found that 340 mg l(-1) of silver was dissolved in 3 M potassium chloride (KCl) internal solution as silver complex ions (AgCl(-(x-1))(x)) for x = 2 or 3. However, only 1.93 mg l(-1) of silver chloride (AgCl) can theoretically be dissolved in water. The complex ion that effused into the sample solution through the liquid junction clogged the liquid junction (e.g. porous ceramic) as AgCl, or as metallic silver (Ag) in reducing solution. Therefore, the constant effusion of KCl internal solution was inhibited, and the liquid junction potential became unstable or fluctuating. A new reference electrode was developed, which can eliminate AgCl(-(x-1))(x) in 3 M KCl internal solution by the use of chelating resins. A combination of this reference electrode with a pH electrode made long-term stable pH measurements possible.     

Behaviour of silver—silver malonate and silver—silver succinate electrodes in aqueous media

The silver—silver oxalate electrode has been employed by many workers^1–3 in aqueous media as the second order reference electrode, but no work seems to have been done so far on the study of the behaviour of silver—silver malonate and silver—silver succinate electrodes. The present work deals with the study of these electrodes in ionic equilibria of malonate and succinate ions in aqueous media. These electrodes, in conjunction with a saturated calomel electrode, have been employed in the poten- tiometric determination of malonate and succinate ions in aqueous media. In additon, the effect of the added salts, such as, potassium nitrate and sucrose on the behaviour of these electrodes has also been examined in this media.     

Meeting the Requirements of the Silver/Silver Chloride Reference Electrode

Potentiometric cells from which the pH values of standard buffer solutions are computed rely on the silver–silver chloride reference electrode which has proved to be convenient, reproducible and reliable. Of the various methods of preparation of silver-silver chloride electrodes only one concerns us here: the thermal–electrolytic type that has been used more extensively than any other form. Once prepared, the electrodes need to be equilibrated before use and between experiments. The equilibration technique must ensure voltage stability and inter-electrode, or bias, potential below 0.1 mV. In potentiometry the stability of a reference electrode is of utmost importance since an offset of 1 mV is equivalent to a deviation of about 0.02 in the pH value.     

Determination of low levels of cyanide with a silver/silver sulphide wire electrode

A silver/silver sulphide electrode is prepred quickly by holding a cleaned silver wire in vapours from molten sulphur. In 1000–10 mg l^?1 cyanide solutions, the electrode exhibits a linear E/log C_CN function which becomes slightly sinusoidal for 10–0.1 mg l^–1 cyanide. The average slope is slightl super-Nerstian (10 mV/decade concentration). The applicability of the electrode is demonstrated for the determinations of microgram quantities of water-soluble cyanide from the Prussian blue pigments which are constituents of externally applied cosmetics. The home-made electrode provides results agreing with those obtained with commercially available electrodes.     

Raman spectroscopic investigation of silver electrodes

Raman spectroscopy has been applied to the study of the reduction of carbon dioxide and of formate and carbonate ions at a silver electrode. Raman spectra of adsorbed intermediate species, which are as yet only partially identified, have been detected and show marked variations with electrode potential. These spectral variations are clearly correlated with the voltammetric features for carbonate solutions and suggest that these reduction products complicate most measurements on silver electrodes in the cathodic region. The interpretation of the previously reported spectra due to adsorbed pyridine at silver electrodes has been reconsidered; interactions with surface carboxy species may be significant.     

A self-generating third-order electrode: Part II. Analytical applications of the silver—silver sulphide electrode

Analytical applications of the silver—silver sulphide electrode are illustrated by potentiometric determinations of Cd(II) and Pb(II) ions. The stability of the electrode potential in the presence of oxidizing agents is demonstrated by various titrations with silver(I) solutions. The influence of pH on the electrode potential in pure acidic solutions is noted. The electrode used was prepared by electrolytic deposition of silver sulphide on a silver rod; after 2 years, it remained reliable, and was unaffected by light under normal laboratory conditions.     

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.     

Behaviour of glass and silver/silver chloride electrodes in some non-aqueous media

The stability of glass electrodes and silver/silver chloride electrodes in isopropanol, methyl ethyl ketone and a mixture of equal volumes of these has been measured, and found to be of the order of 1 mV. Changes in the electrode potential due to addition of water and to addition of supporting electrolyte have been investigated. The glass electrode responded reversibly to hydrogen ion activity changes in buffers of picric acid-tetraethylammonium picrate, and perchloric acid-di-isopropylamine. The autoprotolysis constants at 25 degrees were calculated to be 2 x 10(-19) in isopropanol, 2 x 10(-26) in the ketone and 8 x 10(-19) in the mixture.     

Potentiometric determination of tetraphenylborate with silver nitrate

A simple potentiometric method for determining the tctraphenylborate ion (C₆H₅)₄B- contents of organic amine tetraphcnylborate salts has been developed. The compounds arc dissolved in 1 : 1 aqueous acetone; and the solution is buffered at a pH of 5 with 3M acetic acid and 3M sodium acetate. The resulting solution is then titrated with 0.06N aqueous silver nitrate, using a silver indicating electrode, a glass reference electrode and a Beckman pH meter to indicate EMF changes. Platinum electrodes in conjunction with the Malmstadt automatic titrator can also be used. Good end-points were obtained for all structure types except the primary aromatic amine borates. Values for (C₆H₅)₄B- found were within 2% of theory for 22 compounds so analyzed.     

Electrolytic determination of nanomolar concentrations of silver in solution with a piezoelectric quartz crystal

Silver in solution is determined in situ by the frequency change of a piezoelectric quartz crystal on electrodeposition on the electrode of the crystal. The electrolyte solution flows through a cell containing the platinum-plated electrode (cathode) of the quartz crystal, a coiled platinum-wire anode and a silver—silver(I) chloride reference electrode, and is electrolyzed at —0.2 V vs. $\text{Ag}\text{AgCl}$. The frequency change is proportional to the silver concentration in the range 10^-5–5 × 10^-7 M after electrodeposition for 5 min, and in the range 10^-8–10^-9 M by recycling 20 ml of the solution over the electrodes for 3 h.     

Potentiometric determination of silver(I) by selective membrane electrode based on derivative of porphyrin.

The performance of silver metal complexes with meso-tetraphenylporphyrin ([H2T(4-CH3)]PP) as ionophores for ion-selective electrodes was studied. The electrode exhibited linear response with Nernstian slope of 59.2 +/- 1.0 mV per decade within the concentration range of 1.0 x 10(-7)-1.0 x 10(-1) M silver ions. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot, was 1.0 x 10(-7) M. The response time of the electrode was < 10 s over the entire concentration range. The silver-selective electrode exhibited good selectivity for Ag(I) with respect to alkali, alkaline earth and heavy metal ions. The electrodes could be used at least three months without a considerable divergence in their potential. The electrodes are suitable for use in aqueous solutions in a wide pH range of 3.0-9.0. They were used as indicator electrodes in titration of Ag(I) with sodium iodide solution and were successfully applied to direct determination of silver in real samples.     

The effect of composition of solid silver amalgam electrodes on their electrochemical response

The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed that the AgSAE 30/70 contained only one single phase (Ag₂Hg₃), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III) chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes.     

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.     

The behaviour of mixed metal sulphide/silver suphide sensing materials in solutions of silver ions

Hydrophobized graphite electrodes activated with CuS/Ag₂S can be used to measure silver ion activities as effectively as silver sulphide electrodes, whereas electrodes activatd with PbS/Ag₂S or CdS/Ag₂S are useless for this purpose. The CuS/Ag₂S electrode is also suitable for use in potentiometric titrations involving species that are not contained in the sensing material, but are capable of producing precipitates with silver or sulphide ions.     

Roughened silver electrodes for use in metal-enhanced fluorescence

Roughened silver electrodes are widely used for surface-enhanced Raman scattering (SERS). We tested roughened silver electrodes for metal-enhanced fluorescence. Constant current between two silver electrodes in pure water resulted in the growth of fractal-like structures on the cathode. This electrode was coated with a monolayer of human serum albumin (HSA) protein that had been labeled with a fluorescent dye, indocyanine green (ICG). The fluorescence intensity of ICG-HSA on the roughened electrode increased by approximately 50-fold relative to the unroughened electrode, which was essentially non-fluorescent and increased typically two-fold as compared to the silver anode. No fractal-like structures were observed on the anode. Lifetime measurements showed that at least part of the increased intensity was due to an increased radiative decay rate of ICG. In our opinion, the use of in situ generated roughened silver electrodes will find multifarious applications in analytical chemistry, such as in fluorescence based assays, in an analogous manner to the now widespread use of SERS. To the best of our knowledge this is the first report of roughened silver electrodes for metal-enhanced fluorescence.     

Silver/silver iodide electrodes of the second kind as sensors for cyanide

Silver/silver iodide electrodes of the second kind prepared by electrolytic coating of silver electrodes are advantageous as sensors for cyanide. They are inexpensive and exhibit characteristics similar to those of commercially available ion-selective electrodes. They can be regenerated easily when necessary; this eliminates the lifetime problems generally inherent in iodide electrodes used as cyanide sensors. The preparation, properties and selectivity characteristics of the second-kind iodide electrode are described.     

Potentiometric determination of tetraphenylborate ions with silver nitrate. Determination of silver, potassium and thallium(I)

Summary The potentiometric determination of tetraphenylborate with silver nitrate solution was investigated a) at i=0 in the presence of calomel reference electrode and silver resp. silicone rubber based halide-selective indicator electrodes and b) at i0 in the presence of silver (cathode)-calomel, silver-silver, silver-platinum, platinum-silver and graphite-silver electrode couples. An indirect method is described for the determination of potassium ions with potentiometric end-point indication. Experiments were also carried out in order to develop methods for the titration of silver, potassium and thallium(I) ions with sodium tetraphenylborate solution in the presence of anodic polarized graphite and calomel reference electrodes. The relative standard deviations were 0.38–0.49% for tetraphenylborate, 1.96% for potassium and 1.07% for thallium(I).

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Potentiometrische Bestimmung von Tetraphenylborationen mit Silbernitrat. Bestimmung von Silber, Kalium und Thallium(I)

Zusammenfassung Die Möglichkeit der potentiometrischen Bestimmung von Tetraphenylborat mit Silbernitrat wurde untersucht a) in Anwesenheit von Kalomel-Bezugselektrode und Silber- bzw. haloidselektiven Silicongummi-Indicatorelektroden bei i=0 und b) in Anwesenheit von Silber (Kathode)-Kalomel-, Silber-Silber, Silber-Platin-, Platin-Silber- und Graphit-Silber-Elektrodenpaaren bei i0. Eine Methode zur indirekten potentiometrischen Bestimmung von Kalium sowie Verfahren zur Bestimmung von Silber-, Kalium- und Thallium(I)-ionen mit Natriumtetraphenylboratlösung in Anwesenheit einer anodisch polarisierten Graphitelektrode und einer Kalomel-Referenzelektrode wurden ausgearbeitet. Die relativen Standardabweichungen betragen für Tetraphenylborat 0,38–0,49%, für Kalium und Thallium 1,96 bzw. 1,07%.

     

A potentiometric detector for hydrogen cyanide gas using silver dicyano complex

A sensitive method capable of detecting Hydrogen cyanide gas in atmosphere at its TLV is being presented. This method makes use of two silver electrodes kept in two separate compartments which are in contact with a solution of constant concentration of Silver dicyano complex at a pH 11.5. One of the electrodes used as reference is concealed and the other used for sensing is exposed to the incoming air. In the absence of Hydrogen cyanide gas the potential difference between the two electrodes is zero, but when hydrogen cyanide gas is passed into the cell, the activity of Ag(+) ions nearer to the sensing electrode changes, there by generating a potential difference between the two electrodes. The plot between the potential vs. log of Concentration of Hydrogen cyanide gas is linear, in the concentration range 0.66-42.3 mg/m(3) with a slope nearer to 120mV and regression coefficient around 0.997. The standard deviation is 6% (n=4). Minimum detectable limit is 0.66 mg/m(3). Various concentrations of Silver dicyano complex used gave similar plots.     

New pathway for sonoelectrochemical synthesis of gold–silver alloy nanoparticles from their bulk substrates

In this study, we report the first sonoelectrochemical methods to prepare gold–silver alloy nanoparticles with the mean diameter of 5 nm in 0.1 N HCl aqueous solutions without addition of any stabilizer. First, a silver substrate was roughened by a triangular-wave oxidation–reduction cycle (ORC) in an aqueous containing 0.1 N HCl. Silver-containing complexes were found in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in the same solution containing the silver complexes. After this procedure Au- and Ag-containing complexes were left in the solution. Then the Au working electrode was immediately replaced by a Pt electrode and a cathodic overpotential of 0.6 V from the open circuit potential (OCP) of ca. 0.75 V vs Ag/AgCl was applied under sonification to synthesize Au–Ag alloy nanoparticles.