Separation of trace heavy metals from silver matrix by solid – liquid extraction for graphite-furnace atomic absorption spectrometry

 A silver sample (50–300 mg) was dissolved in 6 mol/l nitric acid and mixed with 6 mol/l hydrochloric acid to form silver chloride. The solution was evaporated to dryness and the residue was treated ultrasonically in 0.1 mol/l nitric acid for the extraction of trace impurities from the silver chloride. Traces of iron, copper, lead and bismuth were recovered in greater than 94% yields, though considerable amounts of cadmium were not extracted due to the strong occlusion in the silver chloride. The separation factor for the silver was about 10^-4; hence the trace heavy metals were immediately determined by graphite-furnace atomic absorption spectrometry without any interference. The validity of the method was confirmed by the analysis of certified reference material. The proposed method is simple and allows the detection of as little as 10 ng/g levels in silver samples. Received: 13 January 1995/Accepted: 29 March 1995     

A simple indirect automatic method to determine total iodine in milk products by flame atomic absorption spectrometry

A simple, precise and accurate automatic method for the determination of total iodine in milk products by indirect atomic absorption spectrometry is proposed. Iodide in solutions resulting from alkaline ashing of samples is precipitated with silver ion in a precipitation-dissolution flow manifold, which allows performing on-line the retention of the silver iodide precipitate formed on a filter, its wash with diluted ammonia and its dissolution with a diluted thiosulfate solution. Dissolved silver is also determined on-line by flame atomic absorption, and the achieved amount of this metal is proportional to that of iodine in the sample. The proposed method is very selective, avoids interferences from anions present in the samples, which can be also precipitated with silver, because these silver compounds are dissolved with ammonia at the washing step. This method allows the determination of iodine in the range 0.011-0.35 μg mL⁻¹ with a relative standard deviation between 1.3 and 6.8% at a rate of ca. 17 samples h⁻¹.     

Electrochemical determination of the absolute cross-section of giant Raman light scattering by silver-silver adatom complexes

The procedure of the determining of changes in the background intensity in the giant Raman light scattering spectra at silver surface in solutions of silver salts, under the action of current changes during galvanostatic silver electrodeposition near the silver electrode equilibrium potential, suggested by authors, is substantiated. Expressions for the calculations of the quantitative values of the absolute background cross-section of the giant Raman light scattering, which is caused by the interaction of the metal electron plasma with silver adatoms, are derived. The relationship between the silver adatom concentration and the back-ground intensity in the giant Raman light scattering spectra allows estimating the absolute cross-section of the background of the giant Raman scattering for the metal-adatom complexes (1.02 × 10⁻²⁷ cm²/adatom) from preliminary experiments in sulfate solutions.     

The giant Raman scattering absolute cross-section for light scattered by the silver-adatom-metal complexes at silver electrodes in silver perchlorate aqueous solutions

The value of giant Raman scattering absolute cross-section for silver adatoms (??_ad = 3.1 × 10^?27 cm²/adatom) is determined by the measuring of the background intensity in the giant Raman scattering spectra at silver electrode surfaces in silver perchlorate solutions. With taking into consideration of the sulfate ion specific adsorption, the improved value ??_ad = 1.9 × 10^?27 cm²/adatom is determined in silver sulfate solutions. The closeness of the values in the two solutions allows concluding that the weakly adsorbing anions affect but negligibly the silver adatom properties; however, in compliance with the earlier data obtained in sulfate solutions, they affect markedly the kinetics of the adatom migration over electrode surface.     

Spectrophotometric determination of copper by flow injection analysis with an on-line reduction column

A silver reductor minicolumn is used ina flow-injection system for reduction of copper(II) to copper(I), which is detected spectrophotometrically using bathocuproine disulphonic acid. The reductor functions very well at flow rates up to 4 ml min^?1; this allows sample injection ar rates up to 120 h^?1. Linear calibration is achieved for 5 × 10^?7– 1 × 10^?4 M copper. The detection limit is 3.4 ng and the midrange precision is 1%.     

An EXAFS study of AgPO3 and AgBaP3O9

The local structure around silver atoms in the crystalline and glassy forms of AgBaP₃O₉ and AgPO₃ has been investigated using Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). The results are reported at the silver K-edge. The structure of AgBaP₃O₉ is representative of isolated silver whereas silver pairs have been evidenced in crystalline AgPO₃. The present investigation allows to detect the formation of Ag⁺-Ag⁺ pairs in both glasses. These data arc consistent with crystal chemistry of silver phosphates and the luminescent properties of these materials.     

Determination of silver in rocks by a stoichiometric radioreagent radioisotope dilution technique

A rapid procedure for the routine determination of nanogram amounts of silver in rocks is described. After dissolution of the sample with a hydrofluoric-nitric-perchloric acid mixture in the presence of ¹¹⁰Ag tracer, the silver is separated by extraction as the dithizonate into xylene and back-extracted into dilute hydrochloric acid. After evaporation and removal of the hydrochloric acid, the silver is taken up in an acetic acid-sodium tartrate buffer solution and reacted with a constant amount of radioactively labelled iodide. The silver iodide formed is isolated by extraction into amyl alcohol and silver is determined by the ratio of the counting rate of the iodide to that of the silver in the silver iodide complex. Results of the analyses of several U.S. Geological Survey standard rocks are given.     

Potentiometric studies on organic compounds containing sulphur with a sulphide ion-selective membrane electrode

Phenylthiourea and N,N-diphenylthiourea can be determined in the concentration range 10¹–10^?3M by potentiometric titration with silver nitrate solution with a sulphide ion-selective membrane electrode. The influence of the alkali and acid concentration on the course of the reactions with the silver nitrate titrant was studied. When phenylthiourea is titrated in the presence of 0.1 M sodium hydroxide, silver sulphide is precipitated, and the phenylcyanamide formed simultaneously reacts further with silver nitrate to form a silver phenylcyanamide precipitate. When N,N-diphenylthiourea is titrated under similar conditions, silver sulphide is again formed, but no cyanamide-type compound can be formed owing to the presence of the second phenyl group. In 1 M sodium hydroxide both compounds studied react with two equivalents of silver to give silver sulphide and phenylurea or diphenylurea, respectively. In the presence of nitric acid both compounds react similarly with silver nitrate. Two molecules of the compounds react with one molecule of silver nitrate to give a white precipitate.     

Electrothermal atomic absorption spectrometric determination of selenium in blood serum and seminal fluid after protein precipitation with trichloroacetic acid

The determination of selenium in body fluids by electrothermal atomic absorption spectrometry (e.a.a.s.) suffers from severe spectral interferences from phosphate which results in overcompensation when a continuum-source background corrector is used. The separation of selenium from phosphate by protein precipitation with trichloroacetic acid allows the determination of selenium in blood serum and seminal fluid by e.a.a.s. after thermal stabilization with silver, nickel or copper. The selenium concentration in seminal fluid from healthy, fertile Norwegian donors ranged from 0.09 to 1.30 μmol l^-1 with a group average of 0.44 μmol l^-1 (n = 15).     

Extraction of metals by neutral sulfur-containing extractants: Part I. o-isopropyl-n-ethylthiocarbamate

The formation of neutral mixed complexes of the MX_mS_p type (where M is a metal ion with m⁺ charge, X the inorganic anion, and S the sulfur-containing extractant) allows a selective extraction of various elements. The extraction of many metals from mineral acid solutions or from halide-sulfuric acid mixtures by 0.05 M O-isopropyl-N-ethylthiocarbamate(IPETC) solution in chloroform has been studied. (IPETC) possesses very high selectivity for silver and mercury ions in extractions from HNO₃, H_{2)SO4, HClO4 and HCl solutions. In addition to silver and mercury, Cu, Au, Tl and Se are readily extracted from solutions containing bromide. From iodide solutions, copper, gold and thallium ions may be selectively extracted because silver and mercury cannot be extracted at concentrations of iodide above 0.1 M.(IPETC} extracts metals as mixed complexes, containing the halide and apparently the extractant in the molecular form.     

Electrochemical Recovery of Silver from Secondary Raw Materials

Electrolysis of silver in 95-84 wt % sulfuric acid with addition of 40 g l^-1 of silver sulfate was studied at electrolyte temperature of 40°C. The optimal conditions of silver electrolysis in 84-85 wt % sulfuric acid were determined. Semicommercial tests of the electrochemical recovery of silver from silver coatings on copper, brass, aluminum, and steel articles were performed.     

Applications analytiques de la phénothiazine

Spot tests carried out with the help of phenothiazine as reagent permit the detection of silver on a drop plate or on paper. D = 10^-5 or even 6.7.IO^-6 with a little less certainty. The reactions obtained are described in detail in the case of palladium, gold and platinum. Use of the reagent allows the detection of iron in presence of uranium (0.15γ iron in 0.053 ml in the presence of 107 times its weight of uranium). It also enables mercury to be detected in the presence of silver, even in the case of silver which is practically free from mercury. Finally, by the combined use of phenothiazine and diphcnylcarbazide it is possible to detect 0.54γ of silver in the presence of 100 times its weight of mercury.     

柠檬酸辅助可控制备花状银粒子及其表面增强拉曼散射性能

以抗坏血酸为还原剂,柠檬酸为结构导向剂,一步还原硝酸银,合成了尺寸和形状可调的花状银颗粒。纳米粒子的粒径可在600～1 200 nm范围内调整,表面突起可达到10～25 nm。柠檬酸的化学性质在银纳米粒子合成多级花状银结构的过程中起着至关重要的作用。通过改变柠檬酸或抗坏血酸溶液的用量,银结构的各向异性形貌可以很容易地调节。以制备的多级花状银颗粒作为表面增强拉曼散射(SERS)基底,对浓度为10~(-10)mol·L~(-1)的罗丹明6G(R6G)仍具有较高的检测灵敏度。     

Potentiometric studies on thioacetamide by means of a sulphide ion-selective membrane electrode

The sulphide ion-selective electrode has been found to be applicable to the determination of thioacetamide in the concentration range of 10^-1–10^-3 M by direct potentiometry and titration with silver nitrate. The effects of the acid and alkali content of the solutions on the titration reaction have been studied. In alkaline and slightly acidic solutions the product of the reaction is silver sulphide; in solutions in which the acid concentration exceeds 0.5 M, a precipitate of silver thioacetamide is formed. If the alkali concentration of the solution is lower than that corresponding to the amount of acid formed during the titration, another potential jump occurs before the end-point owing to the decrease of sulphide'concentration governed by hydrolysis.     

Determination of nitrate by flow-injection analysis with an on-line anion-exchange column

Nitrate (? 6 × 10^-4 M) is determined by displacing thiocyanate froman anion-exchange mini-column and determining it spectrophotometrically after reaction with iron (III). The efficiency of lead- and silver-loaded ion-exchange columns in removing anionic interferences is investigated. It is found necessary to incorporate a copperized cadmium reductor to reduce lead or silver ions released by these columns, which otherwise depress the nitrate response. Incorporation of a lead/silver ion-exchange column allows the determination of nitrate in tap water.     

The reduction process of phytic acid–silver ion system: A pulse radiolysis study

Reduction of silver ion in a silver–phytic acid (1:1 ratio) system has been studied using pulse radiolysis technique. Time-resolved transformation of the intermediates, Ag⁺→Ag⁰→Ag₂⁺→Ag₃²⁺, has been clearly observed in the reduction of silver–phytic acid (1:1) system. The effect of phytic acid on the formation and decay of initial silver clusters has been also studied. The surface plasmon absorption band of stable silver nanoparticle (410 nm) and dynamic light scattering technique has been used to characterize the nanoparticles and measure the average size (R_av=100 nm).     

Le dosage de traces d'argent dans le zinc extra-pur par activation neutronique

Below the p.p.m. level, the determination of silver in zinc by non-destructive γ-spectrometry is no longer feasible due to the activation of the matrix element. The activated zinc is dissolved in nitric acid, sulfamic acid and silver carrier are added, and ^110mAg (253 d) is obtained in a radiochemically pure state after two successive electrolyses on gold cathodes.After two days of irradiation in a thermal neutron flux of the order of 3.10¹³ n/cm²/sec (BR₂-Mol), 30 ng of silver can easily be evaluated with an error of 5%. Data obtained by integral γ-counting or by γ-spectrometry are compared.     

Use of high-voltage electroaccumulation for lowering the detection limit for silver in stripping voltammetry

The use of high-voltage electroaccumulation in the determination of silver by stripping voltammetry at a mechanically renewed graphite electrode with an area of 2.5 × 10⁻³ cm² in 0.2% boric acid acidified with acetic acid at a voltage of 400 V and at an accumulation time of 5 min lowered the detection limit for silver to 1 × 10⁻¹² M.     

Adsorption of ethyl xanthate anions on a silver electrode. An in-situ FTIR study

The adsorption of ethyl xanthatc ion (EX⁻) on a silver electrode in sodium sulphate, phosphate buffer (pH 6.8) and borate buffer (pH 9.2) solutions was studied in situ using Fourier transform IR reflection spectroscopy. The measurements were carried out using a thin-layer flow cell, which allows a continuous supply of the electroactive species into the thin layer. The voltammetric behaviour of the silver electrode in EX⁻-containing solution is characterized by the formation of silver ethyl xanthate (AgEX), which is preceded by a prewave due to chemisorption of ethyl xanthate. An IR band at 1220 cm ⁻¹, assigned to chemisorbed ethyl xanthate, was observed in spectra obtained in the chemisorption region. All IR bands characteristic of AgEX were observed in spectra of a silver electrode surface covered by a few monolayers of AgEX. The in-situ IR measurements also showed that the adsorption of EX⁻ starts directly on the positive side of the potential of zero charge of silver (−0.7 V/SHE).     

Silver particles-modified polysulfonic acid-doped polyaniline layers: electroless deposition of silver in slightly acidic and neutral solutions

Polyaniline layers are produced by electrochemical polymerisation of aniline in the presence of small amounts of poly(2-acryalamido-2-methyl-propane-sulfonic acid) in an inorganic acid solution. Electroactivity and in situ conductance of the obtained polysulfonic acid-doped layers are studied in slightly acidic and neutral solutions. Electroless deposition of silver particles is carried out in silver-EDTA complex ion solutions at pH = 4.2 and pH = 6.6 by using the polyaniline layers as reductant. The amount of electroless-deposited silver is studied depending on: polymerisation charge used to synthesize the polymer layer, pH of the plating solution, metal ion concentration and dipping time. SEM shows in all cases a highly non-homogeneous distribution of the metallic phase over the surface, the most protruding fibrillar polymer structures favouring the electroless silver deposition. A linear dependence between amount of the polyaniline material and amount of deposited silver is found for the silver plating solutions with the highest investigated concentration (10 mmol l⁻¹). At lower concentrations (2.0 and 0.4 mmol l⁻¹), the same amount of silver becomes deposited on polymer layers with markedly different charges. The electroless deposition of silver in the solutions with lower acidity results in lower amounts of deposited silver at otherwise identical conditions. Effects such as charge transfer within the polymer phase and mass transport in the solution are addressed to explain the observed dependencies of the amount of deposited silver on concentration and pH in the different plating solutions.