Determination of cadmium in environmental materials by fast neutron activation analysis

Cadmium is determined by activation analysis with fast neutrons, obtained by irradiation of a thick beryllium target with 14.5-MeV deutrons. Cadmium-111m, formed via the ¹¹²Cd(n, 2n)^111mCd and ¹¹¹Cd(n, n′)^111mCd reactions, is separated by liquid—liquid extraction with zinc dithyldithiocarbamate in chloroform and measured with a Ge(Li) γ-spectrometer. For low concentrations, cadmium is precipitated as cadmium ammonium phosphate after the extraction. NBS and BCR reference materials were analyzed: for concentrations between 3 and 500 μg g^?1, the relative standard deviation ranges from 5 to 3% The results obtained for sewage sludge are compared with those obtained by reactor neutron activation analysis.     

Instrumental neutron activation analysis of tree rings for dendrochemical studies

Instrumental neutron activation analysis (INAA) was employed to determine zinc, cadmium and potassium concentrations in the growth rings of ponderosa pine (Pinus ponderosa Dougl.) trees growing along the shores of Lake Roosevelt in Washington State, U.S.A. where mineral processing activities have resulted in high burdens of zinc and cadmium in the lake sediments. The tree growing along the contaminated waterway display elevated concentrations of zinc in its growth rings relative to a tree growing along an uncontaminated tributary of Lake Roosevelt. Cadmium concentrations in the growth rings from both sites are similar from 1988 to 1993. Water quality data indicate an increased concentration of cadmium in the lake from 1984 to 1988. The increased concentrations of cadmium in the lake water were reflected in apparent increases in concentrations of cadmium in individual rings of the tree sampled at the contaminated site. This suggests that translocation of cadmium in the sapwood of heartwood-forming species does not occur in the short term, and thus may not be a limiting factor in using trees as environmental monitors for cadmium. In addition, five-year tree ring segments were analyzed and subsequently reanalyzed as individual single-year ring segments. The analytical data obtained for the pooled individual rings are essentially the same as for the five-year segments, demonstrating the utility of NAA for dendrochemical studies.     

Determination of traces of cadmium in alloy steels by anodic stripping voltammetry

Concentrations of cadmium of the order of 0.1 ppm in alloy steels containing large concentrations of chromium and nickel (ca. 17 and 13% respectively), about 0.1% of copper and a number of metals at low concentrations, were determined by anodic stripping voltammetry with a hanging mercury-drop electrode in 1M hydrochloric acid. Cadmium was separated on Dowex 50W-X8 cation-exchanger in a medium at pH 1.3 containing excess of EDTA. Mercury-film electrodes cannot be used for this determination, because the peak for cadmium is distorted by evolution of hydrogen on the electrode support. The relative standard deviation of the determination of 0.44 ppm of cadmium in steel is 3.2% and the confidence limits for 95% probability are 0.44 +/- 0.02 ppm. The error in the cadmium recovery does not exceed + 8%.     

Comparison of three Mexican aluminosilicates for the sorption of cadmium

Summary The sorption of cadmium from aqueous solutions was evaluated in three Mexican aluminosilicates (two zeolites and one clay). The effects of pH and contact time on the sorption process were examined. Cadmium was analyzed by neutron activation analysis in the exchanged aluminosilicates. The sorption of cadmium by aluminosilicates was the same in the pH range from 4 to 8, considering the standard deviation. Kinetic studies were carried out and showed a rapid sorption of cadmium in the first 5 hours but the equilibrium was reached in about 20 hours. The sorption kinetics of cadmium ions was best described by the second-order Ritchie modified model. The experimental results obtained in different concentrations and at room temperature for both zeolites were fitted with classical isotherms of Freundlich, Langmuir and Freundlich-Langmuir models. The sorption pattern followed the Langmuir-Freundlich model.     

Determination of Cd(II) in Some Foodstuffs by Anodic Stripping Pulse Voltammetry (ASPV) using Glassy Carbon Electrode

Abstract

Cadmium in the presence of 0.04 M NaCl as the electrolyte was determined using stripping voltammetry with superimposed constant amplitude pulses of negative polarity (SVPNP) or positive polarity (SVPPP), and differential pulses stripping voltammetry using rotating disc glass carbon electrode (RDGCE). The SVPNP was found to give the greatest sensitivity. The anodic peak was obtained at potential ?850 to ?795 mV due to the oxidation of cadmium to cadmium(II). Linear calibration curves were obtained in the concentration range between 1.5×10^?9–2×10^?10 M. The relative standard deviation is 4.25% at very low concentration of 2×10^?10 M. This method was successfully applied to the determination of cadmium in some foodstuffs (wheat and its products, vegetables) after acid digestion.     

Reversibility of cadmium sorption to calcite revisited

Cadmium sorption to calcite was studied in aqueous solution at calco-carbonic (CO(2)-H(2)O-CaCO(3)) equilibrium and at concentrations below the solubility product of otavite (<10(-7) mol L(-1)). Experiments were conducted in a stirred flow-through reactor, lasting for 15 and 60 h at flow rates of 1.6 and 0.5 mL min(-1), respectively. Under both flow conditions, the cadmium breakthrough curves reached steady state after a flow time of about 50 reactor volumes, but different calcite saturation levels were achieved, which implied time-dependent sorption rates. Desorption of cadmium was induced by switching from Cd-containing to Cd-free solution in the reactor inflow. Reversibility of sorption was then evaluated by comparing amounts sorbed and desorbed over identical time intervals. On average, the desorption/sorption ratio was 95±10%. Desorption rates were close to those for sorption and showed the same time dependency: Initially, rates were fast and slowed down with time. "Irreversible" surface reactions such as solid-solution formation could not be inferred. In previous research, cadmium sorption was often shown to be partly irreversible. We surmise that calcite surface ripening is conditioned by the concentration of lattice-building ions in the EDL. At calco-carbonic equilibrium, these ion concentrations at the surface are lowest. Therefore, irreversible binding of cadmium is not favoured.     

Structural and optical investigations of SiO2-CdS core-shell particles

Cadmium sulfide nanoparticles (approximately 5 nm), chemically capped using thioglycerol molecules, have been anchored onto silica particles (approximately 80 nm) functionalized with 3-aminopropyltrimethoxysilane. Transmission electron microscopy clearly showed that at a low concentration of cadmium sulfide, nanoparticles were discretely and more or less uniformly attached onto the silica particles. At a high concentration of cadmium sulfide nanoparticles, an approximately 6-nm-thick compact shell of cadmium sulfide was formed on the silica particles. In both cases the nanocrystalline nature of cadmium sulfide particles was preserved, as is evident from X-ray diffraction and optical absorption spectra.     

Determination of trace cadmium in environmental water samples using ion-interaction reversed-phase liquid chromatography with fluorescence detection

An ion-interaction reversed-phase liquid chromatographic method has been developed for the determination of cadmium at low microg/l concentrations in environmental water samples. Cadmium and other matrix metals were separated through on-column complexation with 8-hydroxyquinoline sulphonate, using an octadecylsilica column and a mobile phase containing 15% acetonitrile, 10-13 mM tetrabutylammonium hydroxide, 5 mM 8-hydroxyquinoline 5-sulphonic acid and 10 mM acetic acid-acetate buffer (pH 4.8-5.4). Under the above conditions Cd(II) could be easily resolved from excess concentrations of matrix metals and could be detected at concentrations as low as 2 microg/l using fluorescence detection at 500 nm (based upon a 100-microl injection). The method showed a slightly curved detector response over the range of interest [up to 1 mg/l Cd(II)] and was successfully applied to the determination of trace Cd(II) in water samples containing large excesses of Mg(II) and Zn(II) and other matrix metals.     

Determination of heavy metals in environmental reference materials using solid sampling graphite furnace AAS

Summary Cadmium and nickel are determined in Coal, Coal Fly Ash and Urban Particulate Matter Reference Materials using solid sampling graphite furnace AAS. The evaluation of integrated absorbance is required to overcome the effect of the matrix on the rate of atomization. The homogeneity of the samples under investigation in the range between 0.3 mg and 1.5 mg sample weight is good enough to make possible relative standard deviations around 10% for cadmium and between 10 and 20% for nickel. Cadmium can be determined against reference solutions, the nickel results are slightly lower than the certified value if calibration is performed against aqueous solutions. Calibration against a solid reference is therefore recommended. Less sensitive resonance lines and an internal gas flow through the tube are required for some of the samples to keep the absorbance in the linear calibration range. The direct determination of chromium in these samples is hampered by the lack of less sensitive resonance lines. Due to high concentrations of chromium in the samples, direct determination without dilution of the sample e.g. by spectrally pure graphite powder is impossible. The peak for the refractory carbide forming element vanadium is strongly suppressed by the Coal and the Urban Particulate matrix. Integration of the signal within a reasonable time and at an atomization temperature of 2650 °C is impossible.

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Bestimmung von Schwermetallen in Umwelt-Referenzmaterialien mit Hilfe der Feststoff-Graphitrohrofen-AAS

     

Use of a nitrate-form anion exchange resin for the determination of traces of gold in copper and cadmium by neutron activation analysis

A method is described for the determination of traces of gold in copper and cadmium by neutron activation analysis, using anion exchange resin as a preconcentration agent: gold was separated from large amount of copper or cadmium with Cl-form Dowex 1X8 AG, 100–200 mesh, resin. To reduce the interfering activities, the resin was irradiated in NO ₃ ⁻ -form and washed with dilute hydrochloric acid after irradiation.¹⁹⁸Au in the resin was then counted with a Ge(Li) or NaI(Tl) detector. The chemical yields were more than 99%. The concentration factors of gold for copper and cadmium samples were 1.1×10⁸ and 2.7×10⁶, respectively. The analytical results of gold in 99.99% copper and 99.999% cadmium were 65 and 0.15 ppb, respectively. The blank was 0.05 ng Au per 200 mg of wet resin.     

Characteristics of Subtractive Anodic Stripping Voltammetry of Lead,Cadmium and Thallium at Silver‐Gold Alloy Electrodes

Silver‐gold alloy electrodes have been studied for the purpose of the quantitative determination of heavy metals by subtractive anodic stripping voltammetry, (SASV). The results have been compared with those obtained with the silver and gold electrodes. The 50/50 a/o Ag/Au alloy electrode is the most suitable for quantifying thallium in the presence of lead and cadmium. The separation of its peak from those of lead and cadmium is 200 mV, which is about twice the separation obtained on the pure metal electrodes and is also better than on mercury. The silver electrode is suitable for the simultaneous determination of thallium, lead and cadmium. The peaks of lead and cadmium overlap on the 50/50 alloy. Pure silver or pure gold can be used for simultaneous quantification of these two metals. The use of gold for quantifying lead and cadmium is more limited because the peak potential of cadmium is shifted in the negative direction as its concentration increases and at [Cd²⁺]>200 nM, the two peaks merge. SASV enables correction for background currents and is of utmost importance for obtaining well‐defined peaks. The peaks of lead, cadmium and thallium appear over a relatively narrow potential range (ca. 200 mV) on all the electrodes presented in this work. For this reason, the quantifying of a peak is based on the derivative at the inflection point of only one of its branches (ascending or descending). All SASV measurements were carried out without removal of oxygen.     

Determination of trace impurities in some nickel compounds by flame atomic absorption spectrometry after solid phase extraction using Amberlite XAD-16 resin

A simple flame atomic absorption spectrometric (FAAS) procedure for the determination of lead, bismuth, gold, palladium and cadmium as impurities in Raney nickel and nickel oxide was developed using a preconcentration step on an Amberlite XAD-16 resin packed column. Lead, bismuth, gold, palladium and cadmium were quantitatively recovered and separated from a solution containing 1 M HCl and 0.3 M NaI by the column system. Effects of the various parameters such as reagent concentrations, sample volume, matrix effects, etc. have been investigated. Under optimized conditions, the relative standard deviation of the combined method of sample treatment, preconcentration and determination with FAAS (n = 7) is generally lower than 12%. The limit of detection (3s, n = 20) was between 10–270 ng/g. The results were used for separation and preconcentration of five trace elements from nickel matrices.     

Adsorption of Cadmium onto Hematite: Temperature Dependence

Cadmium adsorption by hematite has been investigated at 25-100 degrees C. The evaluation of experimental data was made, using the three-plain ( identical withFe(+)ellipsis identical withFeO(-)ellipsiscounter plain) constant capacitance model. The structure of hematite surface and of cadmium complexes was also considered. The computer program for calculation of cadmium adsorption onto hematite at 25-100 degrees C in 0-1m NaNO(3) is available. Copyright 2001 Academic Press.     

Electrothermal atomic absorption spectrometric determination of ng g-1 levels of cadmium in bone after dithizone extractions

After removal of lipid and acid digestion of bone samples, cadmium is separated from the matrix by two extractions with dithizone in carbon tetrachloride. The first extraction at pH 3–3.5 removes cadmium from the matrix; the second extraction, at pH 8.5 in the presence of 2-hydroxyethylethylenediaminetriacetic acid, is needed to prevent suppression of the cadmium signal by zinc. Cadmium is finally measured in the back-extract into 0.24 M hydrochloric acid. Less than 10 ng g^-1 cadmium in fresh bone can be determined within a relative standard deviation of 10%.     

Quartz Crystal Microbalance for Selenite Sensing Based on Growth of Cadmium Selenite Crystals Immobilized on a Monolayer of Phosphorylated 11-Mercapto-1-Undecanol

 A quartz crystal microbalance (QCM) sensor for selenite ions in aqueous solution was constructed based on crystal formation of cadmium selenite, immobilized with a self-assembly monolayer (SAM) of phosphorylated 11-mercapto-1-undecanol (MUD) on a QCM gold electrode surface. The mass change caused by the selective adsorption of selenite ions on the cadmium selenite crystals at the solid/solution interface was detected by the QCM. The response (−ΔF) of the modified QCM oscillator increased with increasing selenite ion concentrations in sample solutions, ranging from 9.7×10⁻⁵ to 9.0×10⁻⁴ M at pH 7.4. The synthetic process of anchoring cadmium selenite crystals on the phosphorylated MUD organic film was also followed by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The atomic concentrations measured by XPS confirmed the crystal growth of cadmium selenite on the phosphorylated MUD SAM at the QCM gold electrode surface. From the AFM images, changes in surface topographic features were followed: the MUD SAM and phosphorylated MUD on the QCM gold electrode had similar surface roughness; however the difference for the cadmium selenite film on the phosphorylated MUD SAM was clearly seen. The observed QCM frequency change of the modified QCM oscillator per unit time was found to be proportional to the square of the supersaturation of cadmium selenite, indicating the crystal growth of cadmium selenite at the solid/solution interface. The modified QCM oscillator exhibited selectively strong QCM response to SeO₃ ²⁻ ion. In contrast, the responses to tested interfering anions were almost negligible. The order of anion selectivities of the present modified QCM sensor was SeO₃ ²⁻≫CO₃ ²⁻>SeO²⁻ ₄, SO₄ ²⁻, Br⁻, I⁻, NO₃ ⁻. These selectivities were basically attributable to the differences in solubility products and solubilities for the salts of each anion with cadmium (II) ion. Received May 12, 1998. Revision December 29, 1998.     

Determination of cadmium in biological and environmental samples by slurry electrothermal atomic absorption spectrometry

The retention of cadmium by the bacteria Escherichia coli and Pseudomonas putida was optimized in order to develop a rapid and selective preconcentration method for cadmium from biological and environmental samples prior to determination by electrothermal atomic absorption spectrometry. Living and lyophilized cells for both bacteria were used, but the method using dead cells shows better analytical capabilities. Cadmium from aqueous solutions is easily retained on the outer membrane of both bacteria in the pH range 4-10, although the selected working pHs for E. coli and P. putida were 5 and 9, respectively. Cadmium retained by the bacteria was dispersed in 3.5 M nitric acid and the slurry was introduced directly into the graphite tube. The best sensitivity and detection limit were obtained for E. coli (0.03 ng ml(-1) and 0.04 ng ml(-1) respectively, in the absence of any chemical modifier). A strong spectral interference from nickel chloride was found and methods to overcome it were developed. The proposed extraction procedure was tested by the determination of cadmium in different standard biological and environmental samples.     

生物吸附剂—虾壳吸附镉（Ⅱ）的实验研究

本文采用廉价的生物吸附剂一虾壳来吸附水中的Cd^2 ，研究溶液的pH值，初始Cd^2 离子浓度，虾皮不同粒度，外加盐等因素对Cd^2 的吸附特性的影响，探讨了经过一定浓度酸处理的虾壳对Cd^2 的吸附情况，得到了最佳的pH值，得出了适宜的吸附等温线经验方程。     

Determination of mineral balances in sheep offered feed with added cadmium and zinc

The optimum conditions for microwave digestion of herbage and faeces to determine mineral concentrations were obtained by varying sample mass, reagent and heating programme, and it was confirmed that the resulting element concentrations were the same as for certified reference material. The effects of feeding cadmium to sheep at a level that is typical of polluted regions (1 mg/kg) for ten days were investigated, as well as the possible amelioration of cadmium effects by adding 30 mg/kg Zn to the diet. Cadmium in the feed increased the cadmium balance and produced several mineral disturbances, in particular a reduction in sodium balance which is typical of renal tubular disorders. Including zinc in the diet as well as cadmium reduced the cadmium balance to a level similar to that of sheep that did not receive cadmium or zinc, which suggests that the zinc status is critical in determining whether cadmium in feed increases the cadmium balance in sheep. Received: 1 August 1997 / Revised: 8 December 1997 / Accepted: 10 December 1997     

Preparation and properties of uniform colloidal metal phosphates IV. Cadmium-, nickel-, and manganese(II)-phosphates

Colloidal dispersions of uniform spherical particles of cadmium phosphate, nickel basic phosphate, and manganese (II) phosphate were prepared by aging at elevated temperatures metal salt solutions and phosphoric acid or sodium dihydrogen phosphate in the presence of urea and sodium dodecyl sulfate. Uniform spheres were obtained only if urea and the surfactant were added within a given range of concentrations.The spherical particles were amorphous as prepared. Cadmium phosphate and nickel basic phosphate particles crystallized when calcined at appropriate temperatures. Manganese (II) phosphate particles underwent a phase transformation to crystalline plate-like solids when aged in doubly distilled water at room temperature.Supported by NFS grant CHE-8619509.Part of M. S. Thesis by L.L.S.     

Nondestructive analysis of the gold quarter liras

In this study, we have prepared seven Au-Cu standards in the concentration range of 18–24 (as carat) for nondestructive control of gold quarter liras. Some calibration curves for quantitative analysis of Au in the gold quarter liras that commercially present in Turkey have been plotted using these standard samples. The characteristic X-rays of Au and Cu emitted from these standard samples and the test sample with known composition are recorded by using a Ge(Li) detector. These calibration curves provide a nondestructive analysis of gold quarter liras with the uncertainties about 1.18%.