Trends in sorption preconcentration combined with noble metal determination.

Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.     

New Complexing Polymer Aminothioether Sorbents in the Analytical Control of Recyclable Metal-Containing Raw Material of Rare and Noble Metals

The development and use of thioether sorbents for the separation and preconcentration of metals from aqueous solutions are described. The possibilities of initial polymer thioethers in selective preconcentration and the acceleration of sorption through the introduction of nitrogen-containing groups into thioethers are considered. The dependence of the selectivity of sorbents on the nature of radical at the nitrogen atom is revealed. The use of aminothioethers with different substituents at the nitrogen atom enables distinguishing the groups of noble metals, toxic elements of arsenic and selenium subgroups, and a number of nonferrous metals in the presence of large excesses of other elements. A high recovery of the elements to be determined into the sorption preconcentrate and the selectivity of the sorbents help to improve the accuracy of the analysis. Prospects for the use of aminothioethers are considered on an example of sewage waters. It is found that the extraction of small concentrations of elements from large volumes of solutions is more convenient to carry out in dynamics, for which powdered aminothioether sorbents are not suitable. To ensure a possibility of using aminothioethers in dynamics, a “snake in a cage” synthesis method is used, in which the inert granular support is modified with aminothioether moieties. The introduction of aminothioethers with different radicals at the nitrogen atom makes it possible to combine sorbents selective with respect to different groups of elements on one carrier and thus to create a universal sorbent with predetermined properties, aimed at extracting certain metals.     

Preconcentration of noble metals with the POLYORGS 4 complexing sorbent under the action of microwave irradiation

The sorption of Au(III), Pd(II), Pt(IV), Rh(III), and Ir(IV) with the POLYORGS 4 complexing sorbent in the static mode was studied at room temperature and on thermal and microwave heating. It was demonstrated that the sorption of noble metals from 1 M HCl and 1 M HNO₃ solutions can be substantially accelerated under the action of microwave irradiation. Based on the obtained data, the conditions of the group preconcentration of noble metals for their subsequent determination by the ETAAS and ICP AES methods were selected. The preconcentration procedure was used for the analysis of certified reference material SARM-7B (platinum-containing ore), VT-1 (copper-nickel sulfide ore), and the alloy of copper with noble metals.     

POLYORGS as complexing sorbents for preconcentration of trace metals

Summary The main characteristics of the complexing sorbents POLYORGS are reviewed. These sorbents contain pyrazole, imidazole, amidoxime, 2-mercaptobenzothiazole, thioglycolanilide and arsenazo groups and exhibit high selectivity in respect to noble, rare-earth and heavy metals. The sorbents POLYORGS are applied for the preconcentration of these metals to be determined in ores, rocks, natural and waste waters, and industrial products. The metal determinations after preconcentration are carried out by means of different instrumental methods (e.g., AAS, XRFA, ICP-AES, NAA) either directly in the sorbent, after elution of the analytes or decomposition of the sorbent.     

X-ray fluorescence and atomic emission determination of cobalt in water using polyurethane foam sorbents

The conditions of analytical signal formation during direct X-ray fluorescence and arc atomic emission determination of metals using polyurethane foam sorbents were studied. A sorption spectroscopic technique of cobalt determination in water with preconcentration in the form of thiocyanate complexes based on simple ethers using polyurethane foam sorbents was developed. The linear calibration range was two orders of magnitude. With a cobalt concentration from 25 ml of water in the static mode, the lower limit of the metal content was 3 and 9 μg/l for X-ray fluorescence and atomic emission methods, respectively.     

A selective sorbent for concentrating noble metals

New chelating sorbents have been synthesized by aminating chloromethylated styrenedivinylbenzene macroporous copolymers with 3(5)-methylpyrazole. The sorption of noble metals from acid solutions and the selectivity has been studied. The sorbents are of interest for selective concentration and extraction of the noble metals.     

New chelating sorbents for noble metals

The properties of the new ehelate-forming “POLYORGS” sorbents for concentration of noble metals are discussed. POLYORGS are made from different polymeric matrices (polystyrene, copolymers of styréne with divinylbenzene, fibrous materials). They contain heterocyclic amine and amidoxime groups, and are selective for noble metals. Some methods of noble metal determination after preliminary concentration of POLYORGS sorbents are given.     

Specificity of noble metals dynamic sorption preconcentration on reversed-phase sorbents

The reversible sorption preconcentration of noble metals (NMs) using different schemes “sorbent–reagent–eluent” was investigated. The extraction of Au, Pd, Pt, Ir, Rh and Ru chlorocomplexes from hydrochloric acid solutions on hyper-crosslinked polysterene MN-200 in the form of ion associates with tributylamine (TBA) and 4-(n-octyl)diethylenetriamine (ODETA) was investigated. It was found that Pd, Pt and Au were quantitatively and reversibly extracted using TBA on hyper-crosslinked polysterene; the appropriate eluent for desorption was 1 M solution of HCl in ethanol. Ir, Rh and Ru under these conditions were not sorbed quantitatively. It was found that sorbent hydrophobicity is not the main characteristic that defines the efficiency of sorption of a particular NM ion associate. Different efficiencies of hyper-crosslinked polysterene MN-200 for sorption of square-planar chlorcomplexes of Pt, Pd and Au and octahedral complexes of Ir, Rh and Ru were found. For the first time, the sorbents with their own N-atoms – StrataX and StrataX-AW – were used for the sorption of Ir, Rh and Ru. Using these sorbents, the sorption of Ir was increased up to 95%, and the sorption of Ru and Rh was increased to about 40%. We can explain these results by nonspecific interaction of chlorcomplexes of Ir, Rh and Ru with ethylenediamine groups of the sorbent. Weak bases with large anions may be applied for desorption of Ir, Rh and Ru. Two schemes of dynamic sorption preconcentration of NMs from hydrochloric acid solutions were proposed – hyper-crosslinked polysterene MN-200 for the determination of Au, Pd, Pt, and StrataX-AW for Ir, Rh and Ru.     

Preconcentration of Trace Elements in Water for Speciation Studies

Trace element speciation has recently become one of the most important problems in water analysis. Proper combination of preconcentration techniques with instrumental determination methods is essential to speciation analysis, because sensitivity and selectivity of direct determination methods are generally lacking. The present paper describes such preconcentration techniques as filtration, centrifugation, flotation and sorption, which have been developed in the author's laboratory for the speciation of heavy metals in river and pond waters by electron microscopy, X-ray microanalysis and chemical analysis. The application of freeze concentration to the speciation of silica in high-purity waters is also discussed.     

On-line coupling of sorption preconcentration to liquid-chromatographic methods of analysis

Methods of analysis combining the on-line sorption preconcentration of analytes with their subsequent separation and determination by high-performance liquid chromatography are considered. Approaches to the selection of sorbents, the sizes of preconcentration columns, and the sorption and desorption conditions are discussed along with the corresponding instrumentation. Many examples of the determination of organic compounds of different polarity and organic and inorganic ions are presented.     

Synthesis and efficiency of a spherical macroporous epoxy-polyamide chelating resin for preconcentrating and separating trace noble metal ions

The determination of noble metals in various materials usually requires their preconcentration and separation from other elements. In spite of the improvements in analytical instrumentation and the development of new analytical techniques such as ICP-MS, which are capable of detecting metal ions at ppt levels, the interference caused by the sample matrix still exists and is perhaps the most serious problem, making a pre-determination enrichment step necessary. Thus, the search for efficient preconcentration and separation methods is essential. A series of chelating resins that can selectively adsorb noble metal ions from aqueous solutions have been described. Functional groups, such as salicylaldoxime and thiosemicarbazide have been incorporated in cross-linked polymers or porous silica gel. These resins have very high selectivity for one or several types of noble metal ion. However, desorption of noble metals from these resins is usually difficult. Hence, the development of an adsorbent from which noble metals can be easily desorbed is needed. In this paper, a new spherical macroporous epoxy-polyamide chelating resin that met this requirement was synthesized by one step reaction. The synthesis of the resin was safe, rapid and more simple and economical than many report adsorbents. Meanwhile, the resin showed more advantages: better acid and alkali resistance; higher adsorption capacity and lower preconcentration concentrations. A resin column procedure combined with inductively coupled plasma atomic emission spectrometry (ICP-AES) for the determination of trace Rh(III), Ru(III) and Ir(IV) in real samples was established.     

Automated on-line preconcentration of palladium on different sorbents and its determination in environmental samples

The determination of noble metals in environmental samples is of increasing importance. Palladium is often employed as a catalyst in chemical industry and is also used with platinum and rhodium in motor car catalytic converters which might cause environmental pollution problems. Two different sorbents for palladium preconcentration in different samples were investigated: silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel) and [1,5-Bis(2-pyridyl)-3-sulphophenyI methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex lx8-200)]. The sorbents were tested in a micro-column, placed in the auto-sampler arm, at the flow rate 2.8 mL min(-1). Elution was performed with 4 M HCl and 4 M HNO3, respectively. Satisfactory results were obtained for two sorbents.     

Sorption Preconcentration and Gas-Chromatographic Determination of Aminazin in Biological Fluids

The sorption characteristics of the drug aminazin on unmodified and chemically modified silicas were examined. The effects of pH and ionic strength on the sorption of aminazin are discussed. Sorption isotherms of aminazin on all of the sorbents were adequately described by the Langmuir equation. The distribution coefficients and the maximum specific adsorption of this compound on the test sorbents were calculated. A highly sensitive and well-reproducible procedure was developed for determining aminazin in biological fluids. This procedure involves sorption preconcentration and gas-chromatographic determination with a thermionic detector.     

Flow Sorption–Spectroscopic Analysis

Combinations of the dynamic sorption preconcentration of elements with spectroscopic determination techniques was considered. The use of sorption systems in flow spectroscopic techniques are discussed, and the evaluation of the efficiency of these systems in the preconcentration of elements is described. The application of flow sorption–spectroscopic techniques to the determination of elements in natural water, drinking water, soil, food stuffs, rocks, and ores is surveyed.     

Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.     

Preconcentration of gaseous organic pollutants in the atmosphere

Three basic methods of preconcentration of organic atmospheric pollutants, viz. by cold trap, absorption in solutions and adsorption on solids at ambient temperature, and methods of liberating the trapped components, are discussed. Adsorption on solids is becoming more widely employed because of its advantages, and selection of the most appropriate sorbent for a given group of pollutants is of major importance. The characteristics of individual types of sorbents are presented, as well as the basic methods of determination of sorption capacity.     

Properties of new fibrous adsorbents with amidoxyme and hydrazidine groups

Data on sorption properties of new fibrous adsorbents with respect to heavy metals are presented. The POLYORGS 34 and POLYORGS 35 filled fibrous adsorbents and POLYORGS 33 fibrous adsorbent contain amidoxyme and hydrazidine groups. Is has been shown that these adsorbents can be used for the adsorption preconcentration of heavy, noble, and rare metals and radionuclides from aqueous salt solutions. Examples of using adsorbents under study for the dynamic preconcentration of copper from a 0.5 M NaCl solution during filtration through a series of disks, column, or adsorption cartridges are presented.     

Sorption methods of concentrating noble metals

Summary The possibility of concentrating microamounts of noble metals on inorganic collectors and chelating sorbents has been investigated. Optimum conditions have been found for simultaneous concentration of Pd, Pt, Rh, Ir, Au and Ag from solutions of complicated composition. For trace analysis a method is suggested based on co-precipitation of the noble metals on copper sulphide, with separation from large amounts of Ni, Co, Fe and associated components. For separation of the noble metals from copper, thin-layer chromatography or sorption on a chelating sorbent under static conditions can be used. The purity of the concentrations obtained allows use of various methods of determination: spectral, atomic-absorption, radioactivation etc.

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Zusammenfassung Die Möglichkeit, Edelmetalle in Mikromengen an anorganischen Kollektoren und Chelatbildnern anzureichern, wurde untersucht. Optimale Bedingungen für die gleichzeitige Anreicherung von Pd, Pt, Rh, Ir, Au und Ag aus Lösungen komplizierter Zusammensetzung wurden gefunden. Für spurenanalytische Zwecke eignet sich die Mitfällung von Edelmetallen mit Kupfersulfid, wobei sie von Ni, Co, Fe und sonstigen Begleitstoffen getrennt werden. Zur Trennung von Kupfer kann die Dünnschichtchromatographie oder die Adsorption an Chelatbildnern unter statischen Bedingungen dienen. Die Reinheit der Konzentrate ermöglicht dann die Bestimmung durch Spektralanalyse, Atomarabsorption, Aktivierungsanalyse usw.

     

Determination of Trace Noble Metals in Natural Samples Using Hyphenated Methods

An approach was proposed to analyzing platinum-containing materials. It involves the high-temperature dissolution of samples in acids under the action of microwave radiation, the sorption preconcentration of noble metals on complexing adsorbents, and their instrumental determination after the microwave dissolution of the concentrate.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 5, 2005, pp. 536–541.Original Russian Text Copyright © 2005 by Kubrakova, Myasoedova, Shumskaya, Kudinova, Zakharchenko, Mokhodoeva.     

On-line preconcentration and separation of palladium, platinum and iridium using alpha-amino pyridine resin with flame atomic absorption spectrometry

A flow injection on-line microcolumn method has been studied for the separation and preconcentration of noble metals, Pd, Pt and Ir, followed by flame AAS determination. An alpha-amino pyridine resin was used as preconcentration reagent. Non-noble metals studied could be eliminated by 2M HCl solution in the rinsing stage. A group-eluent for all Pd, Pt and Ir was studied. Separation of individual noble metals could also be accomplished using selective eluents. This approach can be used both for the separation and determination of Pd, Pt and Ir in samples. The sensitivities and the sample frequency have been improved. The method has been applied to certified samples.