Interferences and their elimination in the determination of the noble metals by atomic-absorption spectrophotometry

A number of serious interferences in the determination of the noble metals by atomic-absorption spectrophotometry have been investigated, and ways of eliminating them considered. The use of the nitrous oxide and acetylene flame reduced many of the interferences but also reduced the sensitivity. Additions of lanthanum, copper sulphate, copper + cadmium sulphate, uranium, and vanadium as releasing agents were effective in the removal of interferences for one or more of the noble metals in the air-acetylene flame. Uranium additions were found to be effective in removing mutual interferences associated with the noble metals (osmium and indium were not tested) whereas vanadium removed mutual and base-metal interferences. The precision and accuracy of methods of analysis based on the use of uranium and vanadium were acceptable, and the application of these methods to the analysis of noble metals collected by various procedures is briefly discussed.     

New masking liquids for the analysis of supported catalysts and functional materials by small-angle X-ray scattering

A new contrasting procedure is proposed for studying supported catalysts and functional materials by small-angle scattering. The main advantage over earlier analogues is the use of new masking liquids, which possess very low X-ray absorption at a relatively high density. A number of supported catalysts were studied using the new procedure, and almost complete agreement of the particle-size distributions of supported metals with transmission electron-microscopic data was demonstrated. The use of the new contrasting procedure on a typical small-angle diffractometer makes it possible to obtain the particle-size distributions of metals in supported catalysts containing noble metals at a level to 0.1 wt %.     

Heavy metal content of a medicinal moss tea for hypertension

The content of various heavy metals (arsenic, cadmium, chromium, copper, iron, lead, mercury, nickel, manganese and zinc) in the moss species Rhodobryum ontariense (Kindb.) Kindb. and its tea are presented in this study. Pursuant to the use of this tea in traditional Chinese medicine for hypertension, the aim of this study was to examine its safety in regard to the metals. All heavy metals were determined by adequate EPA methods. The concentrations of all metals for daily intake in its tea were below the safety levels for human consumption. These results indicate the importance of manganese in R. ontariense tea traditionally used for hypertension and other heart disorders.     

Microwave extraction of heavy metals from wet rhizosphere soils and its application to evaluation of bioavailability

Single microwave extraction of heavy metals Cr, Ni, Zn, Cu, Cd, and Pb by the extractants CaCl(2), EDTA, CH(3)COOH and HCl has been established. The experimental conditions were optimized. A microwave power of 60% and an extraction time of 25 min were adopted. Comparison of microwave extraction and conventional extraction methods revealed that results obtained by microwave techniques were generally in a good agreement with those obtained by use of extraction methods; use of the former resulted in substantial time saving and a better precision, however. Microwave extraction was used to evaluate the bioavailability of heavy metals in soils. Single correlation analysis was performed to establish the relationship between the concentrations of the extractable heavy metals in wet rhizosphere soils and their concentrations in wheat ( Troticum aestivum L.) grown on the soils under greenhouse conditions. The correlation coefficients between the extractable metals in soils and their concentrations in wheat roots were found to be 0.5398-0.7819, 0.6425-0.8073, 0.5568-0.8276, 0.5851-0.6087 for the extractants CaCl(2), EDTA, CH(3)COOH, and HCl, respectively.     

Effect of Environmental Pollution on Heavy Metals Content of Withania Somnifera

Heavy metals were investigated in the medicinal plant Withania somnifera as well as of the soil it was grown in using atomic absorption spectrophotometer. The plant samples were collected from three different locations of N.W.F.P, Pakistan. The plant parts including roots, stem, leaves and fruits were found to have the quantity of heavy metals corresponding to their content in the soil. The purpose of the study is to create awareness among people about the proper use and collection of medicinal plants containing high levels of heavy metals and their adverse health affects.     

Analysis of trace metals in water by in-situ sample pre-concentration combined with wavelength dispersive X-ray fluorescence spectroscopy and inductively coupled plasma-optical emission spectroscopy

In this paper an earlier work on the use of poly(acrylamidoxime) cloth for use as a passive monitor for trace metals in water by characterizing the sorption of several metals onto the cloth using a continuous flow chamber is extended. The monitors consists of amidoxime chelating groups covalently bound to the surface of a textile encased in a common 35 mm slide holder. Placement of this device in the water to be sampled resulted in the uptake of heavy metals by the chelating groups. After removal of the monitor from water, the metals were analyzed using wavelength dispersive X-ray fluorescence spectroscopy (WDXRF) as well as by acid extraction followed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Correlation between the two methods of analysis varied with maximum correlation of 0.99897 observed for Pb and a minimum correlation of 0.16512 for Mg. The order of the distribution coefficients for the seven metals tested was: Pb> or =Cu>Zn>Cd>Mn>Fe>Mg, in agreement with the order of the stability constants for the amidoxime/hydroxamic acid group for the chelation of the same metals at a pH of 5, with the exception of Fe. Field testing of the monitors was also carried out and a comparison made between active sampling of river water and sampling with the monitors. Results indicated that semiquantitative analysis of trace metals in water may be performed using the passive monitors.     

Thin-layer chromatographic behavior of a number of metals on carboxymethyl-cellulose in sulfuric acid and ammonium sulfate media

Summary The thin-layer chromatographic behavior of 57 metals on a weakly acidic cation exchanger, carboxymethyl (CM) cellulose, has investigated systematically in sulfuric acid (0.01–1.0 M) and the acidic ammonium sulfate media. Thin-layer plates of a microcrystalline cellulose, Avicel SF, were also used to compare with the chromatographic behavior of the metals in the acidic sulfate system. The Rf values obtained for many metals tested on CM-cellulose plates increase with increasing concentration of sulfuric acid. Most of metals tested are distributed chromatographically on the CM-cellulose in the low acid concentration. The characteristic retention of many metals, including sulfato-complexes forming metals, on the CM-cellulose can be observed in ammonium sulfate solutions of a low concentration of the acid. Useful multicomponent separations of analytical interest on CM-cellulose layers are presented to demonstrate the use of Rf measurements for predicting separations in the acid and the acidic ammonium sulfate systems.     

Improved recovery of trace amounts of gold (III), palladium (II) and platinum (IV) from large amounts of associated base metals using anion-exchange resins

The adsorption and desorption behaviors of gold (III), palladium (II) and platinum (IV) were surveyed in column chromatographic systems consisting of one of the conventional anion-exchange resins of large ion-exchange capacity and dilute thiourea solutions. The noble metals were strongly adsorbed on the anion-exchange resins from dilute hydrochloric acid, while most base metals did not show any marked adsorbability. These facts made it possible to separate the noble metals from a large quantity of base metals such as Ag (I), Al (III), Co (II), Cu (II), ¶Fe (III), Mn (II), Ni (II), Pb (II), and Zn (II). Although it used to be very difficult to desorb the noble metals from the resins used, the difficulty was easily overcome by use of dilute thiourea solutions as an eluant. In the present study, as little as 1.00 μg of the respective noble metals was quantitatively separated and recovered from as much as ca. 10 mg of a number of metals on a small column by elution with a small amount of dilute thiourea solution. The present systems should be applicable to the separation, concentration and recovery of traces of the noble metals from a number of base metals coexisting in a more extended range of amounts and ratios.     

Electrochemical study of heavy metals and metallothionein in yeast Yarrowia lipolytica

The bioaccumulation of heavy metals (cadmium, nickel, cobalt and zinc) and the effect of these metals on the production of metallothionein and metallothionein-like proteins (MT) in Yarrowia lipolytica was studied by electrochemical methods. The concentrations of heavy metals were determined by differential pulse voltammetry (DPV). A combination of the constant current chronopotentiometric stripping analysis (CPSA) and adsorptive transfer stripping technique (AdTS) was used to determine the content of MT in cells. Both the bioaccumulation of heavy metals and the production of MT in different cell compartments of Y. lipolytica exposed to heavy metals were monitored. The LD(50) of each metal was determined from the number of viable cells in yeast cultures: LD(50)Cd (37.5 microM), LD(50)Ni (570 microM), LD(50)Co (700 microM), and LD(50)Zn (1800 microM). The highest concentrations of heavy metals were found in the cell wall and membrane debris while the lowest concentrations were detected in the cytoplasm. Cadmium and nickel showed the most significant effect on the production of MT. This study provides new insights into the ecophysiology of microorganisms and demonstrates the potential use of these electrochemical methods in biotechnology.     

Improved recovery of trace amounts of gold (III), palladium (II) and platinum (IV) from large amounts of associated base metals using anion-exchange resins

The adsorption and desorption behaviors of gold (III), palladium (II) and platinum (IV) were surveyed in column chromatographic systems consisting of one of the conventional anion-exchange resins of large ion-exchange capacity and dilute thiourea solutions. The noble metals were strongly adsorbed on the anion-exchange resins from dilute hydrochloric acid, while most base metals did not show any marked adsorbability. These facts made it possible to separate the noble metals from a large quantity of base metals such as Ag (I), Al (III), Co (II), Cu (II), Fe (III), Mn (II), Ni (II), Pb (II), and Zn (II). Although it used to be very difficult to desorb the noble metals from the resins used, the difficulty was easily overcome by use of dilute thiourea solutions as an eluant. In the present study, as little as 1.00 microg of the respective noble metals was quantitatively separated and recovered from as much as ca. 10 mg of a number of metals on a small column by elution with a small amount of dilute thiourea solution. The present systems should be applicable to the separation, concentration and recovery of traces of the noble metals from a number of base metals coexisting in a more extended range of amounts and ratios.     

Thermal stabilization of inorganic and organically- bound tellurium for electrothermal atomic absorption spectrometry

The thermal stabilization of inorganic tellurium(IV) and organically-bound tellurium for electrothermal atomic absorption spectrometric determination of the element was studied with the use of the isotope tellurium-127m. Of the 19 metals and potassium iodide tested, 15 metals had a stabilizing effect on inorganic tellurium; among the 9 metals tested with organically-bound tellurium, only 3 exhibited an effect. The most effective metals for stabilizing inorganic tellurium were cadmium, copper, palladium, platinum and zinc, while the best agents for stabilization of organically-bound tellurium were silver, palladium and platinum; in the presence of palladium and platinum, tellurium in both forms could be heated in the graphite tube to 1050°C without losses. Attempts were made to determine tellurium in human whole blood and garlic, but the concentrations were found to be below the detection limits of 3 ng ml^-1 and 140 ng g^-1, respectively.     

Liquid/liquid extraction of metal ions with a polythioether derivative in its reduced bis-mercapto form or its oxidized disulphide form

A linear tetrathioether with thiol groups at both ends, 3,6,9,12-tetrathio-12,14-tetradecanedithiol (TTTD), and its oxidized form, HTCH, a cyclic polythioether containing a disulphide group, were synthesized. The extraction of metal ions by HTCH in the presence of picrate ions is similar to that by a typical thiacrown, 1,4,7,10,13,16-hexathiacyclooctadecane, which has the same number of cyclic sulphur atoms, but is different from that with TTTD. Class ab metals and class b metals react with TTTD. However, most reaction products of these metals are not extracted but form precipitates, except for copper (II), which is ? 99% extracted. These results suggest that the selective separation of metals is possible by the combined use of HTCH and TTTD.     

Direct determination of metals in milligram masses and microlitre volumes by direct-current argon-plasma emission spectrometry with sample introduction by electrothermal vaporization

The development of an electrothermal vaporization and direct-current argon-plasma emission spectrometric system which allowed the determination of metals in microlitre volumes and milligram masses is described. For the five metals investigated, the concentration detection limits were comparable to those for conventional pneumatic nebulization of solutions, and the mass detection limits were superior. The use of an ashing stage was found to reduce enhancement by sodium in the determination of copper and manganese by the plasma method. The system was shown to give accurate results for complex biological, nutritional, water and geological samples.     

A Novel Mechanism for the Extraction of Metals from Water to Ionic Liquids

We present a novel mechanism for the extraction of metals from aqueous phases to room-temperature ionic liquids (ILs) by use of a high-temperature salt as an extraction agent. The mechanism capitalizes on the fact that charged metal complexes are soluble in ILs; this allows for extraction of charged complexes rather than the neutral species, which are formed by conventional approaches. The use of a well-chosen extraction agent also suppresses the competing ion-exchange mechanism, thus preventing degradation of the ionic liquid. The approach permits the use of excess extractant to drive the recovery of metals in high yield. This work presents both a thermodynamic framework for understanding the approach and experimental verification of the process in a range of different ILs. The method has great potential value in the recovery of metals, water purification and nuclear materials processing.     

Sorption preconcentration in combined methods for the determination of noble metals

Combined methods for the determination of noble metals with the use of sorption preconcentration with complexing, anion-exchange, and other sorbents are reviewed. Characteristics of sorbents, techniques of sorption preconcentration, and techniques for the preparation of a concentrate for determination are considered. Features of instrumental methods for the determination of noble metals in the analysis of different materials are discussed. Examples of the use of sorption preconcentration in combined methods for the determination of noble metals are given from publications between 1996–2005.     

Low-temperature synthesis of phthalocyanine and its metal complexes

Conditions for synthesizing unsubstituted phthalocyanine and its metal complexes from phthalonitrile at low temperatures (0–50°C) are optimized. Phthalocyanine and phthalocyaninates are produced under these conditions using activated Rieke metals, metals on inert substrate, sources of “soluble” metals in the form of unstable metal complexes, zeolites, solid-phase electrosynthesis of phthalonitrile, and UV irradiation. The use of pyrophoric metals is found to be the most efficient due to a large number of defects in their structure favoring the initial stage of phthalonitrile cyclization on a metal matrix. The suggested mechanism of formation of phthalocyanine macrocycle assumes participation of metal agglomerates occurring in activated metals.     

Cleansing contaminated seawaters using marine cyanobacteria: evaluation of trace metal removal from the medium

The use of microbial biomass in biosorption is already being studied as a potential alternative to (or combined with) conventional processes, where several algae and microorganisms have already shown promising ability to uptake metals. Cyanobacteria (blue-green algae) are widespread organisms, with specific properties, such as high nutrient removal capacity and tolerance to highly variable conditions which make them well-suited for wastewater and remediation purposes. The main aim of this work was to evaluate the use of a marine cyanobacterium LEANCYA 21 (Synechocystis sp.), collected from the Portuguese southern border, for the removal of selected trace metals when in natural seawater culture medium. It was observed, for the first time, that this particular strain is capable of uptaking Pb, Ni and Zn (at nM levels) from seawater solutions using small amounts of biomass. Uptake values for Pb were up to 90% (0.75 mg g^?1 biomass) in 6 h. The specific biosorption curves of Ni and Zn showed that these metals follow a first order kinetics biosorption in batch conditions. Solutions containing multimetals have revealed that Ni uptake is affected by the presence of Pb and Zn. The calculated specific absorption values were high enough to predict a possible application in aquaculture where such low levels of metals may inhibit microalgae growth.     

Preparation of Silver Nanoparticles‐Based Sensors for the Electrochemical Detection of Thiourea in Leaching Solutions of Waste Electrical and Electronic Equipment

Waste of electrical and electronic equipment is an interesting secondary resource of base and precious metals. Particularly the use of thiourea‐leaching in acidic medium was proposed for noble metals recovery. In this work, a novel and easy‐to‐use electrochemical sensor was developed, aimed to test thiourea from leaching solutions containing significant thiourea and copper amounts. The sensor was constructed using silver nanoparticles (AgNPs) deposited on screen‐printed electrodes. Its performance was studied in a synthetic leaching solution; changes in the overall surface charge of AgNPs resulting in changes in the charge‐transfer resistance for the copper ions were evaluated by electrochemical impedance spectroscopy.     

Investigation of heavy metals mobility in shrimp aquaculture sludge—Comparison of two sequential extraction procedures

Influence of heavy metals was investigated by conducting various tests on the samples collected from aquaculture shrimp in Selangor, Malaysia. The concentration of heavy metals in the sludge and potential of mobility based on its association forms was studied. Two sequential extraction methods (five stages Tessier method and three steps BCR method) were used to determine the binding forms of the metals.From the analysis, Ca, Fe and Mn were found to be highest concentrated metals compared to Zn, Cu, Cr, Cd and Pb in aquaculture shrimp sludge. From the sequential extraction, Cd, Mn and Pb were mostly found in exchangeable/carbonate form, showed its susceptibility to be leached easily. Also Cu and Zn were extracted predominantly in oxidizable form. All metal concentrations (except Cd, Zn and Cu) were extracted to be higher in residual fraction in this method. The results of BCR method are totally similar to the five stages Tessier method. By comparing the percent of recovery, the BCR method was better than Tessier method. Nevertheless for both methods the percent of their recoveries were acceptable. For Pseudototal metal digestion, although the concentration of Cd is less than other heavy metals, it is very harmful as a fertilizer because Cd is one of the heavy metals that might be in the leaf or fruit of plants. Also for investigation of Ca in the sludge, this element was measured and high amounts of that show sludge is useful for growing of plant. The results of direct digestion of heavy metals show that with the control of Cd in this sludge we can use this sludge as fertilizer in soils for agriculture but it is better if it is used for fruitless plants.     

High frequency titrations involving chelation with ethylenediaminetetraacetic acid: Complexation with rare earths

High frequency titrations have been utilized in studying the chelation of rare earth metals with ethylenediaminetetraacetic acid. The use of high frequency titrations for the determination of rare earth metals has also been studied. A procedure is proposed based on direct titrations with disodium ethylenediaminetetraacetate in buffered solutions. Excellent end-points are obtained and the method is accurate in the absence of other metals that might react with the titrant.