Effect of cadmium on the accumulation of arsenic in a marine green alga,Dunaliellasp.

To investigate the effect of cadmium on the accumulation of arsenic by Dunaliella sp., the arsenic accumulated in the alga was determined as a function of time for coexistence of the algae with arsenic and cadmium, with batch methodology. Growth of Dunaliella sp. was affected by addition of arsenic (Na₂HAsO₄.7H₂O) and cadmium (CdCl.2.5H₂O). Growth inhibition of Dunaliella sp. was accelerated by coexistence of arsenic and cadmium. The content of arsenic in Dunaliella sp. became a maximum at 15 h after exposure. The arsenic content in the cells was influenced by addition of cadmium to the solution; the arsenic content in the alga derived from growth in a 10 mg As dm ^?3 solution decreased from 2.7 mg g^?1 in the absence of cadmium to 0.35 mg g^?1 for the addition of 100 mg Cd dm^?3. Dunaliella sp. accumulated cadmium in large quantities but, in conditions of coexistence with arsenic and cadmium, the cadmium content in cells decreased with an increase in the concentration of arsenic in the growth medium Cadmium accumulation by Dunaliella sp. was observed in dead cells although arsenic accumulation was not observed. About 85% of arsenic in the cells was in the water-soluble fraction. On the other hand, about 42% of cadmium in the cells was in the water-soluble fraction, and about 55% was in a fraction soluble in cold trichloroacetic acid.     

Cadmium complexation by aspartate. NMR studies and crystal structure of polymeric Cd(AspH)NO3

Two cadmium compounds containing the aspartate ligand are described, with compositions Cd(AspH)NO₃ and Cd(Asp). The crystal structure of the first shows it is a two dimensional polymer in which each cadmium is coordinated to seven oxygen atoms, four from carboxylates and three from the nitrate moiety which acts both as a chelate and as a bridging ligand. For Cd(Asp), ¹¹¹Cd NMR studies suggests the presence of CdNH₂ interaction.     

SI-traceable certification of the amount content of cadmium below the ng g–1 level in blood samples by isotope dilution ICP–MS applied as a primary method of measurement

The development and implementation of a method for the certification of cadmium in blood samples at low ng g^–1 and sub ng g^–1 levels is described. The analytical procedure is based on inductively coupled plasma isotope dilution mass spectrometry (ICP–IDMS) applied as a primary method of measurement. Two different sample digestion methods, an optimized microwave digestion procedure using HNO₃ and H₂O₂ as oxidizing agents and a high-pressure asher digestion procedure, were developed and compared. The very high salt content of the digests and the high molybdenum content, which can cause oxide-based interferences with the Cd isotopes, were reduced by a chromatographic matrix separation step using an anion-exchange resin. All isotope ratio measurements were performed by a quadrupole ICP–MS equipped with an ultrasonic nebulizer with membrane desolvator. This sample introduction set-up was used to increase sensitivity and minimize the formation of oxides (less MoO⁺ interference with the Cd isotopes). Because of the very low Cd concentrations in the samples and the resulting need to minimize the procedural blank as much as possible, all sample-processing steps were performed in a clean room environment. Detection limits of 0.005 ng g^–1 Cd were achieved using sample weights of 2.7 g. The method described was used to re-certify the cadmium content of three different blood reference materials from the Community Bureau of Reference (BCR) of the European Commission (BCR-194, BCR-195, BCR-196). Cadmium concentrations ranged between ～0.2 ng g^–1 and ～12 ng g^–1. For these materials, SI-traceable certified values including total uncertainty budgets according to ISO and Eurachem guidelines were established.     

Synthesis and characterization of a new cadmium complex based on 1,1-diamino-2,2-dinitroethylene

A new cadmium complex of 1,1-diamino-2,2-dinitroethylene (FOX-7) was synthesized and structurally determined. Central Cd²⁺ is coordinated by six nitrogens from four NH₃ molecules and two FOX-7^? anions to form an octahedral structure. The thermal decomposition of Cd(NH₃)₄(FOX-7)₂ was studied with differential scanning calorimeter and TG–DTG methods. The apparent activation energy and pre-exponential constant of the exothermic process are 220.6 kJ M^?1 and 10^17.86 s^?1, respectively. Cd(NH₃)₄(FOX-7)₂ is sensitive.     

Chemical separation of enriched cadmium target from copper backing in cyclotron production of radioisotope 111In

A radiochemical purification procedure was developed for the separation of enriched cadmium (¹¹¹Cd and ¹¹²Cd) from natural copper that used as backing; and was based upon the chromatographic adsorption. The separation of copper from cadmium was studied in this work. The ions were selectively separated from aqueous solution. Ion-exchange chromatography was employed as a column (1.5 cm i.d. and 15 cm length) with AG1-X8 resin (chloride form, 100–200 mesh) and a flow rate of 1–2 ml/min throughout the separation. 6 M HCl media was used for the adsorption of Cd and Cu on the resin. Then, Cu was eluted by 2 M HCl and Cd by 100 ml 0.5 M HNO₃. The amount of Cu and Cd ions in the final solution (0.5 M HNO₃) were measured by pulse polarographic method and the concentration of Cu was found to be <0.1 ppm. The Cd was quantitatively recovered and the recovery yield from ion-exchange chromatography was greater than 96 %.     

Co-microprecipitation/flotation of trace amounts of cadmium from environmental samples through its complexation with iodide and neutralization with cetyltrimethylammonium bromide in the presence of perchlorate ions

ABSTRACT

A fast, cost-effective and reliable method is presented for separation and preconcentration of trace amounts of cadmium based on co-precipitation and flotation prior to its flame atomic absorption (AAS) spectrometric determination. Cadmium (II) was complexed with iodide and neutralized with cetyltrimethylammonium bromide (CTAB) in the presence of perchlorate ions. This resulted in the formation of a bulky precipitate containing the ternary complex of CdI₄(CTA)₂, floating on the top of the solution. The aqueous layer was then simply drained out, the floated layer was dissolved in 1.0 mL of acetonitrile, and its Cd content was determined by flame atomic absorption spectrometry. The parameters affecting the designed separation method such as KI, CTAB, and ClO₄^? concentration, pH, ionic strength, volumes of sample and dissolving solvent, and extraction time were studied and optimized. For preconcentration of 200 mL of the sample, the calibration graph was linear in the range of 1–30 μg L^?1 of cadmium with a correlation coefficient of 0.9997, enhancement factor of 194 and a limit of detection of 0.18 μg L^?1. The relative standard deviation for seven replicate determinations at 20 μg L^?1 levels of cadmium was found to be 2.1%. The effect of the presence of different common cations and anions on the separation and determination of Cd(II) by the developed method was studied. The method was successfully applied to the determination of trace amounts of Cd(II) ions in different types of real samples including tap water, polluted industrial wastewater, dust, and soil with the recoveries in the range of 95.3 to 103.4.     

A new three‐dimensional anionic cadmium(II) dicyanamide network

A new cadmium dicyanamide complex, poly[tetramethylphosphonium [μ‐chlorido‐di‐μ‐dicyanamido‐κ⁴N¹:N⁵‐cadmium(II)]], [(CH₃)₄P][Cd(NCNCN)₂Cl], was synthesized by the reaction of tetramethylphosphonium chloride, cadmium nitrate tetrahydrate and sodium dicyanamide in aqueous solution. In the crystal structure, each Cd^II atom is octahedrally coordinated by four terminal N atoms from four anionic dicyanamide (dca) ligands and by two chloride ligands. The dicyanamide ligands play two different roles in the building up of the structure; one role results in the formation of [Cd(dca)Cl]₂ building blocks, while the other links the building blocks into a three‐dimensional structure. The anionic framework exhibits a solvent‐accessible void of 673.8 ų, amounting to 47.44% of the total unit‐cell volume. The cavities in the network are occupied by pairs of tetramethylphosphonium cations.     

Determination of cadmium in oyster tissue using isotope dilution inductively coupled plasma mass spectrometry: comparison of results obtained in the standard and He/H2 cell modes

An inductively coupled plasma quadrupole mass spectrometer equipped with an octopole collision/reaction cell was used for the determination of cadmium in oyster tissue samples using isotope dilution inductively coupled plasma mass spectrometry. The oyster samples in question were found to contain Mo and Zr. In our feasibility study on a Cd standard solution (10 μg L⁻¹) containing a matrix of Mo (1000 μg L⁻¹) or Zr (250 μg L⁻¹), the potentially interfering species (MoO⁺ or ZrO⁺) present at the analytical mass of cadmium concerned (m/z 111, 112 or 114) was reduced effectively through the use of a mixture of He and H₂ as cell gases. The accuracy of the method was validated by the analysis of a matrix-matched certified reference material (CRM) of NIST SRM 1566b. The CRM was analyzed under the standard and He/H₂ cell modes. Two isotopic pairs of ¹¹⁴Cd/¹¹¹Cd and ¹¹²Cd/¹¹¹Cd were selected for quantification purposes. The recoveries of cadmium obtained in the two cell modes were compared with each other. The validated method was applied successfully to the APMP.QM-P5 pilot study for international comparability purposes.     

Vibrational spectral studies of solutions at elevated temperatures and pressures. X. Raman spectral study of aqueous cadmium bromide solutions at 25 and 200°C

The Raman spectra of cadmium bromide solutions with bromide to cadmium mole ratios varying from 1.0 to 9.74 were studied at 200°C. Factor analysis revealed that three complexes contributed to the spectra. From a comparison with previous results at 25°C these species were identified as CdBr₂, CdBr ₃ ^– , and CdBr ₄ ^2– cadmium existed as the tetrabromo complex, CdBr ₄ ^2– , at mole ratios greater than 5.99. A formation constant of 7±2 was determined for CdBr ₄ ^2– at 200°C. No evidence of Cd(H₂O) ₆ ²⁺ or CdBr⁺ was found, although electroneutrality dictates that one or both of these species must exist at low mole ratios.     

Effect of hydrogen bonding of solvent on the thermodynamic stability of cadmium ethylenediamine complexes

Changes in the stability of the cadmium(ii) ethylenediamine complexes in mixed water—DMSO solvents were studied by pH-metry and calorimetry. Complex cations [Cd(en)]²⁺, [Cd(en)₂]²⁺, and [Cd(en)₃]²⁺ are formed in aqueous solutions, and the [Cd(en)₄]²⁺ complex with a partially dentate ligand is stable in DMSO. An increase in the DMSO content in a solvent increases the stability of the complexes. The maximum increase in logK is observed for coordinatively saturated compounds. The thermodynamics of complexation is discussed from the viewpoint of solvation approach. Principal differences in the influence of aqueous-alcohol and aqueous-aprotic solvents on the stability of the metal amino complexes were revealed. Protolytic solvents exert a destabilizing effect on the multiligand complexes, because the coordination sphere is involved in H bonding.     

Determination of indium in metallic tin and cadmium by substoichiometric neutron activation analysis

The paper deseribes the determination of indium in metallic tin and cadmium metals by the direct method, which is a variant of substoichiometric radioactivation analysis. It is based on substoichiometric extraction of indium diethyldithiocarbamate into carbon tetrachloride. Indium in tin metal was determined by^116mIn (T=54 min), while^115mIn (T=4.5 h), formed by the reaction¹¹⁴Cd(n, γ)¹¹⁵Cd was used for cadmium samples. The irradiated sample was dissolved and the radioactivity of^116mIn or^115mIn, A, was measured. After the separation of indium from the matrix, a known amount of indium, m, was separated substoichiometrically and the radioactivity, a, was measured. Indium was calculated as M_x=m A/a. If a known amount of the element, M, is added to the irradiated sample in advance, the equation for calculation is given as M_x-m A/a−M. By this method, indium can be determined without any consideration of self-shielding and secondary nuclear reaction of the matrix.     

Author index to volume 51

Absolute cross sections for the quenching of Cd(³P₁) and Cd(³P₀) by acetylene, ethylene, propene, cis-2-butene and four fluoroethylenes have been determined by a phase-shift method. It was found that acetylene and olefins quench the triplet cadmium at almost gas-kinetic encounter, while the quenching rates for fluoroethylenes were found to decrease with the increase in the number of substituted fluorine atoms. It was also observed that these molecules do not cause intramultiplet mixing between Cd(³P₁) and Cd(³P₀). The causes of the decrease of the reactivities of fluoroethylenes are discussed.     

The synthesis of nucleus-shell Cd(OH)<Subscript>2</Subscript>/CdS structures by chemical precipitation from aqueous solutions

The region of stable coexistence of Cd(OH)₂ and CdS as a function of pH and the concentration of the complex-forming agent (ammonia) was determined by thermodynamic analysis with the purpose of the preparation of Cd(OH)₂ cadmium hydroxide particles surrounded by cadmium sulfide CdS shells. In this region, powders were obtained by chemical precipitation during various precipitation times from aqueous solutions. X-ray diffraction was used to track the growth of the CdS nanophase of a disordered structure and hexagonal Cd(OH)₂ phase consumption with time. It was found by complexonometry that part of cadmium formed insoluble structures as a result of the formation of continuous nanosized CdS shells on single crystalline Cd(OH)₂ particles. A comparative analysis of the experimental data was used to determine the kinetics of formation of nucleus-shell Cd(OH)₂/CdS particles in the system.     

Comparison of Cadmium Cd2+ and Lead Pb2+ Binding by Fe2O3@SiO2‐EDTA Nanoparticles – Binding Stability and Kinetic Studies

This study describes the synthesis and characterization of ethylenediaminetetraacetic acid (EDTA) functionalized magnetic nanoparticles of 20 nm in size – Fe₃O₄@SiO₂‐EDTA – which were used as a novel magnetic adsorbent for Cd(II) and Pb(II) binding in aqueous medium. These nanoparticles were obtained in two‐stage synthesis: covering by tetraethyl orthosilicate and functionalization with EDTA derivatives. Nanoparticles were characterized using TEM, FT‐IR, and XPS methods. Metal ions were detected under optimized experimental conditions using Differential Pulse Anodic Stripping Voltammetry (DPASV) and Hanging Mercury Drop Electrode (HDME) techniques. We compared the ability of Fe₃O₄@SiO₂‐EDTA to bind cadmium and lead in concentration of 553.9 μg L^?1 and 647.5 μg L^?1, respectively. Obtained results show that the adsorption rate of cadmium binding was very high. The equilibrium for Fe₃O₄@SiO₂‐EDTA‐Cd(II) was reached within 19 min while for the Fe₃O₄@SiO₂‐EDTA‐Pb(II) was reached within 25 minutes. About 2 mg of nanoparticles was enough to bind 87.5 % Cd(II) and 54.1 % Pb(II) content. In the next step the binding capacity of Fe₃O₄@SiO₂‐EDTA nanoparticles was determined. Only 1.265 mg of Fe₃O₄@SiO₂‐EDTA was enough to bind 96.14 % cadmium ions while 5.080 mg of nanoparticles bound 40.83 % lead ions. This phenomenon proves that the studied nanoparticles bind Cd(II) much better than Pb(II). The cadmium ions binding capacity of Fe₃O₄@SiO₂‐EDTA nanoparticles decreased during storage in 0.5 M KCl solution. Two days of Fe₃O₄@SiO₂‐EDTA storage in KCl solution caused the 32 % increase in the amount of nanoparticles required to bind 60 % of cadmium while eight‐days storage caused further increase to 328 %. The performed experiment confirmed that the storage of nanoparticles in solution without any surfactants reduced their binding capacity. The best binding capacity was observed for the nanoparticles prepared directly before the electrochemical measurements.     

New two- and three-coordinate cadmium(II) dialkylamides

Some adducts of the known two-coordinate cadmium disilylamide, Cd[N(SiMe₃)₂]₂, have been studied by ¹H, ²⁹Si, and ¹¹³Cd nuclear magnetic resonance spectroscopy. The physical and spectral properties of three new Cd(NR₂)₂ species are also described.     

A two‐dimensional anionic CdII polymer constructed through dicyanamide coordination bridges

In the search for potential ferroelectric materials, molecular‐based one‐, two‐ and three‐dimensional cadmium(II) organic–inorganic compounds have been of interest as they often display solid–solid phase transitions induced by a variation in temperature. A new cadmium dicyanamide complex, poly[4‐dimethylamino‐1‐ethylpyridin‐1‐ium [tri‐μ‐dicyanamido‐κ⁶N¹:N⁵‐cadmium(II)]], {(C₉H₁₅N₂)[Cd(C₂N₃)₃]}_n, was synthesized by the reaction of 4‐dimethylamino‐1‐ethylpyridin‐1‐ium bromide, cadmium nitrate tetrahydrate and sodium dicyanamide in aqueous solution. In the crystal structure, each Cd^II cation is octahedrally coordinated by six terminal N atoms from six anionic dicyanamide (dca) ligands. Neighbouring Cd^II cations are linked together by dicyanamide bridges to form a two‐dimensional coordination polymer. The organic cations are not involved in the formation of the supramolecular network.     

π-Arene complexes of the main group elements. II. Complexes of cadmium(II) and zinc(II)

π-Arene complexes of cadmium(II) and zinc(II) have been prepared from the first time. The 1:1 complexes Cd(AsF₆)₂. Arene(Arene=hexaethylor hexamethylbenzene, pentamethylbenzene, durene, $\text{p}$-xylene or benzene), Cd(SbF₆)₂. Arene(Arene = hexamethylbenzene, toluene or benzene) and Zn(SbF₆)₂. Arene(Arene = hexamethylbenzene or pentamethylbenzene) are synthesized from the strong acid salt and arene in liquid sulfur dioxide. ¹H and ¹³C NMR spectra are consistent with localized bonding of the arene to the metal cation. Exchange-averaged vn]¹³C chemical shifts for the systems Cd(AsF₆)₂-arene-SO₂ confirm the 1:1 stoichiometry in solution and suggest that the stabilities of the complexes are in the approximate range 0.48 – 2.1 M^?1 for the series benzene-hexamethylbenzene. For the system Cd(AsF₆)₂-C₆Me₆-SO₂, a detailed ¹¹³Cd NMR study is consistent with the solution stoichiometry and stability determined from ¹³C NMR. In general, complexation to an arene produces deshielding of the ¹¹³Cd resonance of Cd(AsF₆)₂.     

Construction of Modified Carbon Paste Electrode for Highly Sensitive Simultaneous Electrochemical Determination of Trace Amounts of Copper (II) and Cadmium (II)

A chemically modified electrode was constructed for rapid, simple, accurate, selective and highly sensitive simultaneous determination of Cu(II) and Cd(II) using square wave anodic stripping voltammetry. The electrode was prepared by incorporation of SiO₂ nanoparticles, coated with a newly synthesized Schiff base, in carbon paste electrode. The limit of detection was found to be 0.28 ng mL^?1 and 0.54 ng mL^?1 for Cu(II) and Cd(II), respectively. The proposed chemically modified electrode was used for the determination of copper and cadmium in several foodstuffs and water samples.     

Interaction between threonine and cadmium cation in [Cd(Thr)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>]<Superscript>2+</Superscript> (<Emphasis Type="Italic">n</Emphasis> = 1–3) complexes: density functional calculations

Structures corresponding to energy minima and the binding of cadmium cation to threo- nine (Thr) in model systems [Cd(Thr) _n ]²⁺ (n = 1–3) were studied theoretically. Quantum chemical computations were performed within the framework of the density functional theory using the B3LYP, BLYP, and P functionals. In the optimized structures of the complexes [CdThr]²⁺ and [Cd(Thr)₂]²⁺, threonine acts as a bidentate ligand and cadmium binds to oxygen atoms of carbonyl and hydroxyl groups with the formation of one and two six-mem- bered rings, respectively. In the complex [Cd(Thr)₃]²⁺, cadmium binds to three nitrogen atoms and three oxygen atoms of carbonyl groups in three Thr molecules to form three five-mem- bered rings.