Stereochimie de la des benzoates d'argent sur des diesters iododesoxy ns: I- Action des benzoates d'argent sur des di-o-aroyl-1,2 iododesoxy-3 ns-glycerols

The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R¹ and R² on the substrates to stabilize a positive charge. Rearrangements are at minimum with R¹ and R² electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed.     

Potentiometric determinations with the silver sulfide membrane electrode : Part I. Determination of cyanide

The possibilities of the silver sulfide membrane electrode for the determination of cyanide are described; determinations by multiple standard addition and titration have been studied, and interferences have been checked. The determination of cyanide in solutions containing various metal complexes, and the evolution method for separation of hydrogen cyanide are discussed. Automatic titration can be used for samples containing 1 p.p.m. cyanide, and the standard addition method for 1 p.p.b. cyanide.     

The preparation and analytical evaluation of a new heterogeneous membrane electrode for cadmium(ii)

The preparation of a new cadmium-selective heterogeneous membrane electrode obtained by hot-pressing a mixture of cadmium and silver sulfides with polythene in a moulding press is described. Nernstian response to cadmium ion was achieved only when the mixture of salts was purified by heat treatment at 600° in an atmosphere of hydrogen sulfide for several hours. This behaviour is discussed in terms of the purity of the salts. Interferences and analytical applications in aqueous and nonaqueous solvents are described.     

A multi-technique surface study of the mercury(II) chalcogenide ion-selective electrode in saline media

X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), rotating disc electrode-electrochemical impedance spectroscopy (RDE-EIS) and synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) have been used to study the response mechanism of the mercury(II) chalcogenide ion-selective electrode (ISE) in saline media. XPS and SIMS have shown that the chalcogenide surface is poisoned by silver chloride, or a mixture of silver halides, on continuous exposure to synthetic and real seawater. Significantly, the in-situ SR-GIXRD study demonstrated that electrode fouling in synthetic seawater is linked to the formation of poorly crystalline or amorphous silver chloride, and that the low level of free mercury(II) in a calibration buffer (i.e., 10(-14) M) is able to undergo metathesis with silver(II) sulfide in the membrane generating mercury(II) sulfide. Significantly, the results of this detailed surface study have shown that silver chloride fouling of the electrode is ameliorated in real seawater comprising natural organic ligands, and this has been attributed to the peptization of silver chloride by the surfactant-like nature of seawater ligands at pH 8. RDE-EIS aging studies have revealed that the chalcogenide membrane experiences a sluggish charge transfer reaction in seawater, and contrary to a previous report for a static electrode, the seawater matrix does not passivate the RDE. The results of this XPS, SIMS, RDE-EIS and SR-GIXRD study have elucidated the response mechanism of the mercury(II) ISE in saline media.     

Bacterial membrane electrode for l-cysteine

Potentiometric response to L-cysteine is obtained by coupling bacteria of the type Proteus morganii to a modified version of a hydrogen sulfide gas-sensing membrane electrode. The resulting electrode system shows good response to cysteine in the millimolar concentration range with moderate selectivity over related sulfur-containing amino acids. The practical applicability of the electrode is limited by the poor discrimination of the internal gas sensor between hydrogen sulfide and carbon dioxide.     

Voltammétrie de l'argent par redissolution anodique sur electrode de carbone vitreux et application au dosage de l'argent dans l'uranium et le pluton

Anodic stripping voltammetry of silver on a glassy carbon electrode, and application to the determination of silver in uranium and plutonium.The use of a glassy carbon electrode for the anodic stripping voltammetry of silver, without deposition of a preliminary mercury film is described. The deposition time, scan rate, rotation speed and molarity of the sulfuric solution have been studied; the method is applied to the determination of silver in uranium and plutonium.     

Potentiometric determination of sulfonamides with a silver sulfide electrode

The silver sulfide membrane electrode shows well-defined responses to several pharmaceutically important sulfonamides over the concentration range 10^-1–10^-4 M. Both direct and titrimetric determinations of sulfonamides are described and applied to pharmaceutical dosage forms.     

Oxydations par le carbonate d'argent—XII : Groupes fonctionnels azotes

Oxidation by silver carbonate on Celite gives azo compounds with primary aromatic amines. Hydrazones are rapidly converted into diazoalkanes, which rearrange into azines. Hydroxylamines give nitrones. Oximes of aromatic aldehydes give nitrile oxides, characterised by their 1,3-dipolar adducts with olefins, nitriles and oximes; 1,2,4-oxadiazoles are obtained in fair yields by this method.     

Analytical Evaluation of the Silver Sulfide Membrane Electrode

Abstract

A membrane electrode selective for sulfide and silver ion has been described. No interferences were found for sulfide ion measurements, and only mercuric ion had a measurable interference with silver ion. Other characteristics of this electrode which are evaluated include speed of response and temperature coefficients. The use of the silver sulfide membrane electrode as an end-point detector in potentiometric titrations under oxidizing conditions is illustrated.     

Etude des interferences spectrophotometriques par utilisation d'une matrice d'experiences factorielle

(Use of a factorial design to study interferences in spectrophotometry.) Ozonation of aqueous solutions leads to the formation of hydrogen peroxide and oxalic acid. Hydrogen peroxide is determined spectrophotometrically by the classical method in which TiO·H₂O₂²⁺ is formed, but oxalic acid interferes by forming a complex with titanium. The interference is studied by using a simple factorial design. The results, calculated by linear regression, show the existence of both translational and rotational effects on the absorbance signals.     

Étude d'équilibres en solution à l'aide des échangeurs d'ions : I Dissociation du perchlorate d'argent et de l'acide nitrique dans les mélanges eau—acide acétique—acide perchlorique ou acide nitrique

A theoretical relationship postulated between the distribution coefficient of a monovalent element and the parameters upon which it depends (acid concentration in solution, dissociation constants of the acid and the salt, selectivity coefficient of exchanged ions) has been verified for the dissociation of silver perchlorate in water—acetic acid—perchloric acid mixtures. The dissociation constants found have been compared with the experimental values obtained by potentiometric measurements. The relationship established has been employed for the determination of nitric acid dissociation constants in water—acetic acid-nitric acid mixtures containing less than 25 % by weight of water. From the results the pK value for nitric acid in pure acetic acid has been evaluated by extrapolation. The theoretical relationship might be used to determine an acid dissociation constant when the dissociation constant of a salt is known and vice versa.     

Oxydations par le carbonate d'argent sur celite—VII : Oxydations de diols

The oxidation of several secondary-tertiary α diols by silver carbonate on Celite is described. In the steroid series, a 17α,20α diol leads to the related ketol, whereas its 17α,20β isomer is either not affected by the reagent, or slowly cleaved to give a 17-keto steroid.     

Étude de l'erreur acide de l'électrode de verre en milieu aqueux: Tome III. Solutions mixtes d'acide et de sel alcalin

The acid error of the glass electrode is studied in mixed solutions of acid and alkaline salt with common anion. Measurements have been made by direct comparison with the hydrogen electrode. The experimental results confirm the view that the acid error arises from anion penetration into the glass. An empirical equation is proposed in which this error is expressed in terms of cation concentration in mixed solution.     

Électrochimie dans l'oxydipropionitrile: Comportement électrochimique du solvant. Stabilité des complexes argent(I) halogénures. Solvatation des anions

Electrochemical possibilities of oxydipropionitrile have been shown. The system Ag(s)/Ag⁺ has been used to make a reference electrode in this medium. The electroactivity range which depends on the electrolyte and the kind of electrode used has been specified. At a platinum electrode, in LiClO₄ medium, the electroactivity range is very large. At a mercury electrode, water does not interfere but at a platinum electrode it is oxidizable; the electroactivity range depends on its concentration. The second part treats the complexes with silver ion and halides. Stability constants of complexes and solubility products have been obtained from potentiometric titration curves. The determination of the transfer parameters for ionic species is based on the Strehlow assumption that the potential of the ferrocene/ferricinium couple is constant in all solvents. The results show that the silver ion is more strongly solvated in oxydipropionitrile than in water; on the other hand halide ions are little solvated in this solvent.     

Étude de l'erreur acide de l'électrode de verre en milieu aqueux: Tome II. Solutions d'acides purs

The acid error of glass electrode is studied in pure acid solutions of different natures by direct comparison with hydrogen electrode. This deviation from the hydrogen function is depending on the nature of both the acid involved and the glass electrode used. The potential of this electrode can be expressed by an empirical formula where two parameters appear: one of them is inversely proportional to molar weight of acid, while the other one is also dependent on the glass electrode used.     

Voltammetry using a dental amalgam electrode for heavy metal monitoring of wines and spirits

We have introduced a non-toxic electrode material similar to dental amalgam for use in voltammetry. Its electrochemical properties are like a silver electrode. However, it possesses a higher overvoltage towards hydrogen than silver, and therefore enables detection of metals like zinc, nickel and cobalt. As such solid electrodes are found to give stable results over several weeks, without any maintenance, and because this method greatly facilitates monitoring of heavy metals, attempts to apply such methods to various samples have been are carried out. The present paper deals with the determination of zinc and lead at nanogram per milliliter levels in wines and spirits with only minor treatment of the samples. The procedure may easily be adapted to continuous monitoring.We have previously found that audible sound may greatly increase the voltammetric signal using liquid mercury as well as silver as electrode material. This is also applied to the actual systems.Finally, model determinations of thallium in brandy with the dental amalgam electrode are compared with atomic absorption spectrometric (AAS) measurements. It was found that the electrode could be used repeatedly, without fouling, and with results close to those found by the AAS method.     

Potentiometric determinations with the silver sulfide membrane electrode : Part II. Determination of Sulfur Compounds

A simple, sensitive and fast titrinetric method for sulfur determinations with the silver sulfide membrane electrode is described. Sulfide and sulfate can be determined in one sample. A sensitive sulfate determination is possible after reduction with hydrogen iodide—sodium hypophosphite—acetic acid. Other inorganic sulfur compounds can also be determined. Sparingly soluble metal sulfides can be determined after treatment with strong acid. A reduction with Raney nickel is suitable for the estimation of elementary sulfur and organic sulfur compounds; combustion of the samples in an oxygen flask may be necessary. The methods outlined are applied to the determination of sulfur in steel, some petroleum products and aerosols. When different methods are used, different kinds of sulfur compounds present in an unknown sample can be distinguished.     

A silver electrode in the potentiometric titration of thiols

A silver wire immersed in a thiol solution gives a potential responsive to the thiol concentration, and is a sensitive indicator electrode in the potentiometric titration of thiols with mercury(II) chloride, p-chloromercuryphenyl sulphonate, and silver nitrate at pH 4.5-9.5, 7-9.5 and 9.5 respectively. Titrations of simple thiols such as cysteine or a protein such as albumin are equally successful, but the potential break was smaller for the protein. The end-point could be determined within an increment of titrant equal to 5 nmole of thiol. An inert atmosphere is needed for titration at pH 7.     

A field electrode method for the determination of sulfide

This paper reports the development of a field electrode method for the determination of total sulfide in water. The method involves the use of preweighed sodium sulfide crystals in the standardization process. Sodium sulfide crystals were weighed and sealed in air-tight plastic volumetric flasks. Standards were prepared in the field by adding a sulfide antioxidant buffer to the flasks containing the sulfide crystals and diluting it to mark with deionized deaerated water. Standards of lower concentration were prepared by serial dilutions of first standards.The results of the reproducibility determination revealed that sulfide concentrations as low as 6 ppb could be measured with a reproducibility of better than ±10%.Water samples were collected from a series of lakes in Fort Bend County, Texas (near Houston) and analyzed for sulfide content. The sulfide ion concentrations of these samples were determined directly in the field by use of an Orion Model 407A/F specific meter equipped with a silver/sulfide ion selective electrode in conjunction with a double junction reference electrode.     

Effect of pH on the response of a cyanide ion-selective electrode

The influence of pH on the cyanide response of a silver iodide membrane electrode has been found to depend on the buffer system employed. A theoretical explanation of the results is attempted by assuming a pH-gradient in the vicinity of the electrode surface.