Voltammetric determination of traces of silver in some metals after dissolution of the sample in mercury

The general possibility of analysing metals and alloys by dissolution of the sample in mercury and recording the anodic voltammogram is examined for the determination of silver in some metals. In order to obtain good separation of the silver peak from the anodic limit, acetonitrile is used in the supporting electrolyte. If the main component of the sample is more noble than mercury, analysis is simple and takes ? 20 min. Significant amounts of base metals in samples must be removed from the amalgam prior to the anodic stripping; optimum conditions for the removal are given. The detection limits found for the determination of silver in gold and lead and in indium amalgam are 4 × 10^?3, 4 × 10^?4 and 4 × 10^?6 % respectively. Dissolution of the lead button in mercury seems to be a successful alternative to the cupellation procedure. Silver in mercury does not form intermetallic compounds with gold.     

Zur Spurenanalyse der Edelmetalle

Zusammenfassung Nano- und Mikrogrammengen der Edelmetalle können durch Amperometrie unter Verwendung von Festelektroden aus Ag oder Au bestimmt werden. Vergiftungen dieser Elektroden werden nicht beobachtet, wenn die Konzentration der zu bestimmenden Edelmetallionen 10^–4 m nicht überschreitet. Die kleinsten noch nachweisbaren Konzentrationen betragen 10^–6 bis 10^–8 m, je nach Element und Methode. Eine Reihe von Elementen stört die Bestimmung, weshalb vor dieser Nanogrammengen der Edelmetalle abgetrennt werden müssen.Über das Verhalten derartig geringer Mengen bei Trennoperationen und Möglichkeiten der Bestimmung von Edelmetallspuren bis zu 0,01 ppm soll im 2. Teil der Arbeit berichtet werden.

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Summary ng and g quantities of noble metals can be determined by amperometry employing solid electrodes of silver or gold. Poisoning of these electrodes is not observed if the concentration of noble metals does not exceed 10^–4 M. The minimum concentration detectable is 10^–6 to 10^–8 M, according to kind of element and procedure applied. As certain elements cause interferences ng quantities of noble metals have to be separated before.The behaviour of such small quantities in separation procedures and the determination of traces of noble metals down to 0.01 ppm will be reported in the 2nd part of this essay.

     

Some noble metals and copper content of italian meteorites as determined by destructive neutron activation analysis

Copper, iridium, platinum and gold content was determined in 15 italian chondritic meteorites by destructive neutron activation analysis. The chemical procedure involves few steps: sample dissolution, group separation of noble metals on inorganic adsorbers and gamma-ray spectrometry. Element content and atomic abundances (Si=10⁶ atoms) are presented and discussed. Precision and accuracy of the analytical method are given as well. Copper, platinum and gold content is within the reported ranges for ordinary chondrites, whereas the iridium content is located on the low side of reported values.     

Study on the effect of collector and inhibitor acid on the floatability of collophane and dolomite in acidic media by TOF-SIMS and XPS

Most of the phosphate ore in southern China is contained within siliceous dolomite phosphate rock, and more than 90% of it is medium and low-grade collophane. Reverse flotation of carbonate gangue minerals (dolomite) from phosphate in acidic media is still the most economical method for the reduction of carbonate in collophane concentrates. It has been recognized that the collophane and dolomite in acidic media affect the surface properties of minerals, thereby affecting their flotation properties. In this paper, HCl and H₃PO₄ were used as regulators or inhibitors to study the flotation behaviour of collophane and dolomite. The inhibition mechanism of collophane and dolomite in two acid media was studied by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) analyses. It was found that the addition of an inhibiting acid can partially depress the collophane and improve the flotation of dolomite, thus achieving their flotation separation, and the inhibition effect of H₃PO₄ on collophane is better than that of HCl. And it was found by TOF-SIMS analysis that the increase in acid concentration did not reduce the adsorption concentration of the collector, and the main reason for the inhibition was not the decrease in the adsorption concentration of the collector. The adsorption capacity of collector on dolomite surface with H₃PO₄ is greater than that with HCl. The XPS test indicated that metaphosphate (PO₃⁻¹) is the pivotal ion for depressing collophane under acid conditions.     

Inductively coupled plasma-atomic emission spectrometry method for determination of trace metals in alkaline-earth matrices after flotation separation

An inductively coupled plasma-atomic emission spectrometry (ICP-AES) method is developed for determination of Cd, Co, Cr, Cu, Ni, Tl and Zn in traces in calcite, CaCO₃, dolomite, CaMg(CO₃)₂, and gypsum, CaSO₄. Interferences of a Ca/Mg matrix on analyte intensities were investigated. The results reveal that Ca does not interfere with Cr, Ni and Zn, but tends to decrease the intensity of the other elements. Magnesium as a matrix element does not interfere on with Zn, but increases the intensities of Ni, Cr and Cu, and decreases the intensities of Cd, Co and Tl. To eliminate these matrix interferences on trace element intensities, a flotation separation method is proposed. Lead(II) hexamethylenedithiocarbamate, Pb(HMDTC)₂, is applied as a collector for flotation of trace elements from acidic solutions of mineral samples. The flotation of acidic aqueous solutions of calcite, dolomite and gypsum was performed at pH 6.0, using 10 mg l⁻¹ Pb and 0.3 mmol l⁻¹ HMDTC⁻ added to 1 l of solution tested. The method detection limits of analytes in different minerals range from 0.02 to 0.06 μg g⁻¹ for Cd, 0.04 to 0.10 μg g⁻¹ for Co, 0.03 to 0.13 μg g⁻¹ for Cr, 0.02 to 0.16 μg g⁻¹ for Cu, 0.09 to 0.30 μg g⁻¹ for Ni, 6.45 to 7.71 μg g⁻¹ for Tl and 0.18 to 0.20 μg g⁻¹ for Zn.     

Highly Selective Nanostructured Electrochemical Sensor Utilizing Densely Packed Ultrathin Gold Nanowires Film

The number of studies conducted about nonenzymatic electrochemical sensors has increased in recent years due to the development of more stable and robust electrodes using noble metals. One of the key aspects for achieving high sensing performance including detection limit and sensitivity is the design of electrode architecture. Herein, we report a new electrochemical sensing platform featuring ultrathin standing gold nanowires (AuNWs) for nonenzymatic detection of hydrogen peroxide (H₂O₂). The use of AuNWs resulted in an increased electron transfer efficiency due to the higher active surface area compared to traditional gold film electrodes. This sensor demonstrates good selectivity, reproducibility, a linear range up to 49.5 mM of H₂O₂ with a sensitivity of 0.185±0.003 mAmM^?1cm^?2 and a limit of detection of 111 μM. The biological relevance of this sensor was tested in cell culture media to illustrate the performance of the proposed sensing electrode in complex biological media.     

Sensitive flotation-spectrophotometric determination of gold based on the gold(III)/bromide/rhodamine 6G system

A very flotation-spectrophotometric method based on the gold(III)/bromide/ tribromide/rhodamine 6G (R6G) system is described. In the presence of bromine, the dibromoderivative (R6G-Br) is formed. The gold compound is floated with di-isopropyl ether, washed with 1 M sulphuric acid and dissolved in methanol, and the absorbance of the solution is measured at 545 nm. The floated compounds is considered to be an adduct of the formula [(R6G-Br⁺)(AuBr^-₄)] · 12[(R6G-Br⁺)[Br^-₃)]. The apparent molar absorptivity is 11.4 × 10⁵] mol^-1 cm^-1. Important interference are Pd, Ag, Hg(II) and Tl(III), belong to the most interfering metals; after a preliminary extraction of gold from acidic bromide medium into di-isopropyl ether, only thallium(III) interferes significantly. The proposed method is applied to determining gold traces in a blister copper samle. Results obtained prove the good precision and accuracy of the method.     

Effects of room-temperature ionic liquids on the chemical vapor generation of gold: Mechanism and analytical application

To get insight into the mechanism of the effect of room-temperature ionic liquids (RTILs) on the chemical vapor generation (CVG) of noble metals, gold was taken as a model element, and eight RTILs were examined. All the RTILs resulted in 3-24 times improvement in sensitivity for Au, depending on their nature. For the RTILs with identical anion, the RTILs with the cations of short chain exhibited better enhancement effect than those with long alkyl chain length or complex branch chain. For the RTILs with identical cation, the RTILs with Br⁻ gave the best enhancement effect. The formation of ion pairs between the cation of RTILs and the anion species of gold via electrostatic interaction, and/or the substitution of the Cl⁻ in the anion species of gold by the anion of RTILs likely enabled a more effective CVG reaction to occur. The RTILs also facilitated the generation of small bubbles and provided an electrostatic stabilization to protect the unstable volatile gold species and to help fast isolation of volatile gold species from the reaction mixture. 1-Butyl-3-methylimidazolium tetrafluoroborate [C₄mim]Br gave the best improvement in the sensitivity (24 times) among the RTILs studied, and also reduced the interferences from common transition and other noble metals. Based on the enhancement effect of [C₄mim]Br, a novel flow injection-CVG-atomic fluorescence spectrometric method with a detection limit (3s) of 1.9 μg L⁻¹ and a precision of 3.1% (50 μg L⁻¹, RSD, n = 11) was developed for the determination of trace gold in geological samples.     

Extraction chromatography of noble metals with use of mixtures of hydrochloric and nitric acid as mobile phases

The chromatographic behaviour of the platinum metals and gold, silver and copper on paper strips treated with liquid anion-exchangers and eluted with mixtures of HNO₃ and HCl was investigated. It was found that increase of HNO₃ concentration in the acid mixture increases the R_F values more significantly than does that of HCl. The presence of HNO₃ in the development solution prevents the reduction of iridium(IV). The R_F values of the noble metals increase in the order Au(III) < Os(IV) < Ir(IV) < Pt(IV) < Pd(II) < Ru(III) < Rh(III) Ir(III). Several separations of noble metals were carried out on paper strips treated with trioctylamine or quaternary alkylammonium salts, as well as the column separation of the mixture Pt---Pd---Rh. The proposed chromatographic systems seem to be especially useful for the separation of non-volatile noble metals.     

Arc atomic emission determination of noble metals in mineral raw materials and products of their processing

A procedure has been developed for the direct atomic emission determination of medium concentrations of noble metals in mineral raw materials and products of their processing. The procedure is based on the application of a spectral complex, consisting of an arc source of spectrum excitation, a DFS-8 spectrograph, a receiver of spectrum emission with CCD structures, and a registration system including software. The detection limits are n × 10^?5% for a number of noble metals and n × 10^?7% for Ag with RSD of 7?C14%.     

The group extraction of noble metals with s-(1-decyl)-N,N'-diphenylisothiouronium bromide and their determination in the organic extract by atomic-absorption spectrometry

The distribution coefficients are given for the noble metals and associated base metals between S-(1-decyI)-N, N'-diphenylisothiouronium (DDTU) in diisobutyl ketone and aqueous solutions containing varying molarities of hydrochloric acid. DDTU is a satisfactory reagent for the extraction of noble metals as a group from most of the associated base metals. Base metals such as iron(III), tin(II), and selenium(IV), which are co-extracted, can be removed from the organic phase by washing with 0.1 M hydrochloric acid; this affects only the recovery of iridium. Although the noble metals cannot be recovered from the organic phase by back-extraction, direct measurement in the organic phase is possible in ths presence of zinc dibenzyldithiocarbamate added as a releasing agent. The final solution for analysis contains 6 mg of additive per 10 ml of solution.     

Simultaneous voltammetric determination of dopamine and ascorbic acid at an electrode modified with the gold-palladium binary system

The catalytic activities of gold, palladium, and rhodium particles and their binary systems electrodeposited on the surface of a glassy-carbon electrode in the oxidation of dopamine and ascorbic acid are compared. As compared to individual noble metals, the Au-Pd binary system exhibits a higher catalytic activity that manifests itself in a multiple increase in the oxidation current of the mediator and in a decrease in the oxidation potential of the substrate. It is found that dopamine and ascorbic acid can be simultaneously determined by voltammetry at an electrode modified with the Au-Pd binary system. The catalytic currents of substrate oxidation are linear functions of the concentrations in the ranges from (1 × 10^?3 to 1 × 10^?7) M for dopamine and from (5 × 10^?3 to 1 × 10^?6) M for ascorbic acid.     

The separation of palladium and platinum by ion flotation

Differences in the ion flotation properties of palladium(II) and platinum(IV) chloro complexes in aqueous solutions are used to achieve separations of these metals. The anionic chloro complex PtCl^2-₆ is floated selectively with cationic surfactants of the type, RNR'₃Br, from solutions of PdCl^2-₄ and various concentrations of hydrochloric acid. The palladium(II) does not float from solutions of ? 3.0 M HCl and the platinum(IV) floated from these solutions can be recovered free of palladium. However, the separation is incomplete as much of the platinum(IV) is also unfloated from these solutions. Quantitative separations are obtained by conversion of the palladium(II) to the cationic ammine, Pd(NH₃)₄²⁺ with aqueous ammonia prior to flotation. The anionic chloro complex of platinum(IV) is unaffected by the presence of ammonia and is floated quantitatively with the surfactant n-hexadecyltri-n-propylammonium bromide from 0.01 M ammonia solutions.     

Development of the principles of an integrated process for extraction of high-purity graphite,gold, and rare earths from carbonaceous rocks

Graphite-bearing rocks of the Ruzhinskaya area (Primorskii Krai, Russia) were found to contain high concentrations of noble and rare earth metals. Industrial exploration of these reserves is restrained by the lack of concentration technique. The application of hydrometallurgy for the production of useful components was studied for the first time. A prospective plan of integrated extraction of high-purity graphite, gold and rare earths using hydrogen fluoride treatment of flotation concentrates was designed.     

Thiourea stripping of rhodium from organic phases resulting from extraction with a mixture of dialkyl sulfide and alkylanilinium nitrate from acid nitrate-nitrite aqueous solutions of triaquatrinitrorhodium(III)

In continuation of our studies on the extraction of rhodium from acid nitrate-nitrite aqueous solutions with a mixture of alkylanilinium nitrate and dialkyl sulfide, a back-extraction of rhodium was studied. Thiourea (TU) is an efficient agent for the back-extraction of rhodium and concomitant noble metals (Pd, Ru, Ag). The back-extraction of rhodium proceeds via coordination mechanism, [Rh(tu)₆](NO₃)₃ being the major product. Aqueous 1 mol/L solution of TU ensures stripping of at least 91% rhodium and provides its relative concentrating up to 4 times (time of phase contact is 5 min, temperature 20?C35°C). The presence of palladium and other noble metals in extract does not affect the Rh stripping.     

Neutron activation analysis of high purity noble metals (palladium,platinum, rhodium,gold and silver)

Methods of neutron activation analysis of high purity noble metals have been developed based on the selective extraction procedures for matrix activities separation. These procedures are shown to provide purification coefficients from matrix of about 10⁶–10⁸. High-resolution gamma-spectrometry makes possible the determination of 25–30 elements simultaneously in aqueous phases remained after matrix separation. Complex standard for NA analysis of pure materials has been described.     

Stabilized Carbenium Ions as Latent,Z‐type Ligands

Controlling the reactivity of transition metals using secondary, σ‐accepting ligands is an active area of investigation that is impacting molecular catalysis. Herein we describe the phosphine gold complexes [(o‐Ph₂P(C₆H₄)Acr)AuCl]⁺ ([ 3 ]⁺; Acr=9‐N‐methylacridinium) and [(o‐Ph₂P(C₆H₄)Xan)AuCl]⁺ ([ 4 ]⁺; Xan=9‐xanthylium) where the electrophilic carbenium moiety is juxtaposed with the metal atom. While only weak interactions occur between the gold atom and the carbenium moiety of these complexes, the more Lewis acidic complex [ 4 ]⁺ readily reacts with chloride to afford a trivalent phosphine gold dichloride derivative ( 7 ) in which the metal atom is covalently bound to the former carbocationic center. This anion‐induced Au^I/Au^III oxidation is accompanied by a conversion of the Lewis acidic carbocationic center in [ 4 ]⁺ into an X‐type ligand in 7 . We conclude that the carbenium moiety of this complex acts as a latent Z‐type ligand poised to increase the Lewis acidity of the gold center, a notion supported by the carbophilic reactivity of these complexes.     

Stabilized Carbenium Ions as Latent,Z‐type Ligands

Controlling the reactivity of transition metals using secondary, σ‐accepting ligands is an active area of investigation that is impacting molecular catalysis. Herein we describe the phosphine gold complexes [(o‐Ph₂P(C₆H₄)Acr)AuCl]⁺ ([ 3 ]⁺; Acr=9‐N‐methylacridinium) and [(o‐Ph₂P(C₆H₄)Xan)AuCl]⁺ ([ 4 ]⁺; Xan=9‐xanthylium) where the electrophilic carbenium moiety is juxtaposed with the metal atom. While only weak interactions occur between the gold atom and the carbenium moiety of these complexes, the more Lewis acidic complex [ 4 ]⁺ readily reacts with chloride to afford a trivalent phosphine gold dichloride derivative ( 7 ) in which the metal atom is covalently bound to the former carbocationic center. This anion‐induced Au^I/Au^III oxidation is accompanied by a conversion of the Lewis acidic carbocationic center in [ 4 ]⁺ into an X‐type ligand in 7 . We conclude that the carbenium moiety of this complex acts as a latent Z‐type ligand poised to increase the Lewis acidity of the gold center, a notion supported by the carbophilic reactivity of these complexes.     

L'ortho-oxy-phénylfluorone,réactif spécifique soit du molybdéne,soit du cuivre

The authors have extended their analytical research on methyl- and ethylfluorone to other derivatives of fluorone, amongst these o-oxyphenylfluorone.This compound is an excellent reagent for molybdenum and the reaction may be made specific for this element by a filter paper technique, The interfering colours, due to the elements As, Fe, V, Ge, Ti, Sn, and Sb are eliminated by using a 20% solution of KF. Under these conditions only copper interferes by giving an indigo-violet colour. By adding 0.5 N sulphuric acid this colour due to copper disappears, whilst that due to molybdenum is unchanged. This reaction, thus made specific for molybdenum, suffers interference only from the presence of oxidising agents which must be removed in a preliminary treatment.The violet colour due to copper, mentioned above, can be used for the detection of copper on the drop plate by treating with hydrogen peroxide which transforms Mo into a permolybdate and adding potassium, tartrate which forms a complex with cobalt. Under these conditions, only copper gives an indigo-violet precipitate and only salts of gold and ruthenium interfere, being precipitated as the metal by the action of H₂O₂. In the absence of these two noble metals (reduced by H₂O₂) the reaction may be considered as specific for Cu⁺².The limit of dilution of the reaction of Mo and Cu is the same and equal to D = 10^-1.5.     

Investigation into the voltammetric behaviour and detection of selenium(IV) at metal electrodes in diverse electrolyte media

The voltammetric behaviour of selenium(IV) was studied at platinum and gold electrodes in sulphuric acid, perchloric acid and potassium chloride media as a basis for its voltammetric detection. The best voltammetric behaviour was recorded at gold electrodes with perchloric acid as the supporting electrolyte. The concomitant presence of metals, such as copper or lead, and of model biomolecules, such as bovine serum albumin, in the solution resulted in a deterioration of the electrochemical response for selenium(IV). Quantitative detection of selenium(IV) by square wave anodic stripping voltammetry at both a millimetre-sized gold disc electrode and a microband electrode array revealed linear responses to selenium concentration in the ranges 5–15 μM and 0.1–10 μM, respectively, with 60 s preconcentration. The sensitivities were 6.4 μA μM⁻¹ cm⁻² and 100 μA μM⁻¹ cm⁻² at the disc and the microband array, respectively. The detection limit at the microband electrode array was 25 nM, illustrating the potentiality of such microelectrodes for the development of mercury-free analytical methods for the trace detection of selenium(IV).