Quantitative Studies of Metal Ion Adsorption on a Chemically Modified Carbon Surface: Adsorption of Cd(II) and Hg(II) on Glutathione Modified Carbon

The adsorption behavior of model toxic metal cations namely Cd(II) and Hg(II) on carbon surfaces chemically modified by glutathione was investigated as a function of the concentration of Cd²⁺ and Hg²⁺ ions, time and the amount of modified carbon used. Square wave and linear sweep anodic stripping voltammetry was used to monitor the uptake of Cd(II) and Hg(II) ions respectively. Kinetic and adsorption isotherm studies reveal that both Cd(II) and Hg(II) ions undergo similar large adsorption with the modified glutathione carbon material (Glu‐carbon).     

Voltammetric Studies of Cadmium‐ and Zinc‐Containing Metallothioneins at Nafion‐Coated Mercury Thin Film Electrodes

Voltammetric studies of rabbit liver metallothioneins (MTs, containing both Zn and Cd ions) and Zn₇‐MT were carried out at Nafion‐coated mercury film electrodes (NCMFEs). The accumulation of MT molecules into the NCMFEs enhances the voltammetric signals and the electrostatic interaction between the Nafion membrane and MT facilitates facile electron transfer reactions. Two well‐defined redox waves, with reduction potential (E_pc) values at ?0.740 and ?1.173 V, respectively, were observed. The peak at E_pc =?0.740 V is attributable to the reduction of the Cd‐MT complex, whereas that at E_pc=?1.173 V was assigned to the reduction of the Zn‐MT complex. Zn₇‐MT exhibits only one redox wave with E_pc=?1.198 V. The NCMFE was found to be more advantageous than thin mercury film electrode (MFE), because the pristine metal ions in MTs (e.g., Cd²⁺ and/or Zn²⁺) are not significantly replaced by Hg²⁺. The NCMFE is also complementary to Nafion‐coated bismuth film electrode in that it has a greater hydrogen overpotential, which allows the reduction of the Zn‐MT complex to be clearly observed. Moreover, intermetallic compound formation between Cd and Zn appears to be less serious at NCMFEs. Consequently, the amounts of Cd and Zn deposited into the electrode upon the reduction reactions can be quantified more accurately.     

Anodic Stripping Voltammetry of Heavy Metals on a Metal Catalyst Free Carbon Nanotube Electrode

Anodic stripping voltammetry (ASV) determination of Pb²⁺, Cd²⁺, and Zn²⁺ was done using metal catalyst free carbon nanotube (MCFCN) electrodes. Osteryoung square wave stripping voltammetry (OSWSV) was selected for detection. The MCFCNTs are synthesized via Carbo Thermal Carbide Conversion method which leads to residual transition metal free in the CNT structure. The new material shows very good results in detecting heavy metal ions, such as Pb²⁺, Cd²⁺, and Zn²⁺. The calculated limits of detection were 13 nM, 32 nM and 50 nM for Pb²⁺, Cd²⁺ and Zn²⁺, respectively with a deposition time of 150 s.     

Electrochemical methods for quantification and characterization of metallothioneins induced in Mytilus galloprovincialis

The quantification of the purified metallothionein (MT) component, isolated from the digestive gland of cadmium-exposed Mytilus galloprovincialis, is described based on the analysis of Cd(II) and SH-groups content, applying electrochemical methods. Advantages and disadvantages of the Brdika procedure for the determination of the MT content is discussed. The saturation of binding positions of purified MT with Cd²⁺ ions can be directly followed voltammetrically. Irrespective of the MT concentration, the saturation with Cd²⁺ of in vivo induced mussel MT is achieved at a molar ratio of 5. Cd²⁺ ions are rapidly displaced from the Cd-Th complex after the addition of Pb²⁺ ions, which indicates the kinetically labile type of the complex.     

Application of Novel Zn‐Ferrite Modified Glassy Carbon Paste Electrode as a Sensor for Determination of Cd(II) in Waste Water

This paper describes the preparation of a new sensor based on Zn‐ferrite modified glassy carbon paste electrode and its electrochemical application for the determination of trace Cd(II) ions in waste waters using differential pulse anodic stripping voltammetry (DPASV). Different Zn/Ni ferrite nanoparticles were synthesized and characterized using scanning electron microscopy (SEM) and X‐ray powder diffraction (XRPD). The prepared ferrite nanoparticles were used for the preparation of Zn‐ferrite‐modified glassy carbon paste electrode (ZnMGCPE) for determination of Cd(II) at nanomolar levels in waste water at pH 5. The different parameters such as conditions of preparation, Zn²⁺/Ni²⁺/Fe²⁺ ratio and electrochemical parameters, percentage of modifier, accumulation time, pH and accumulation potential were investigated. Besides, interference measurements were also evaluated under optimized parameters. The best voltammetric response was observed for ZnFe₂O₄ modifier, when the percentage of modifier was 3 %, accumulation time 9 min, pH of supporting electrolyte 5 and accumulation potential ?1.05 V. Thus prepared electrode displays excellent response to Cd(II) with a detection limit of 0.38 ppb, and selective detection toward Cd(II) was achieved.     

Effects of surface-active substances in square-wave voltammetry and potentiometric stripping analysis of amalgam-forming metal ions

The influence of surface active substances (SAS) (Triton X-100, sodium dodecyl sulfate and dodecyl pyridinium chloride (DPC)) on the potentiometric stripping analysis (PSA), square-wave voltammetry (SWV) and anodic stripping square-wave voltammetry (ASSWV) of Cd²⁺, Cu²⁺, Zn²⁺ and Bi(III) are measured for various contact times and detergent concentrations. Diagnostic criteria for the presence of SAS in electrolytes are reported. Zinc ions accumulate in the adsorbed layer of DPC, probably as a ZnCl⁺ complex. An anomalous dependence of zinc SWV peak currents on the delay time is observed.     

Voltammetry and electrochemical stripping analysis for antimony in aqueous and nonaqueous media after extraction

Cyclic voltammetry of antimony was studied in aqueous media (HCl-LiCl) and in nonaqueous media after extraction with 20% tri-n-butylphosphate in toluene, with a rotating glassy carbon disc electrode. Reduction of antimony to the element in aqueous media is nearly reversible, but irreversible in nonaqueous media. Anodic stripping voltammetric and chronopotentiometric determinations were also studied in nonaqueous media; methanol and LiCI, NH₄SCN or NH₄NO₃, were used as base electrolytes. In nonaqueous media, antimony can be determined down to concentrations of 1O⁻⁸ M by stripping voltammetry, and lO⁻⁷ M by stripping chronopotentiometry. Electrochemical stripping determinations of 10⁻⁶ M antimony(III) were not affected by Co²⁺, Ni²⁺, Cd²⁺, Zn²⁺ or As³⁺ (5 · 10⁻³ M), ag⁺ (4 · 10⁺⁴ M in stripping voltammetry or 10⁻³ M in stripping chronopotentiometry), Hg²⁺ (5 · 10⁻⁴M), Pb²⁺ (3 · 10⁻⁴ M), Cu²⁺ (1.5 · 10⁻⁴ M)Sn²⁺ and Sn⁴⁺ (7 · 10⁻⁴ M), Fe³⁺ (4 · 10⁻⁴ M), Au³⁺ (5 · 10⁻⁵ M) and Bi³⁺ (1.5 · 10⁻⁵ M). Thestripping chronopotentiometric determination showed better selectivity.     

Assessing effects of pH,metal ion and natural organic matter on identification and determination of reduced glutathione by cathodic stripping voltammetry

The effects of pH, metal ions (i.e. Cu²⁺, Cd²⁺, Pb²⁺ and Zn²⁺) and natural organic matter (i.e. Suwannee River natural organic matter standard [SRNOM]) on determination of thiol (i.e. reduced glutathione [GSH]) by cathodic stripping voltammetry were evaluated. pH was the most critical parameter to influence GSH voltammogram (i.e. peak shape, position and height). In presence of Cu and Cd, secondary peaks were found at [metal]/GSH > 1 due to formation of GSH complexes at pH = 8.0 (Cu and Cd) and 2.5 (Cu only). On the other hand, Pb showed negligible influence on GSH voltammogram at pH 8.0 and 2.5 within [Pb]/[GSH] = 0.01–2.0. Zn significantly reduced GSH peak height at pH 2.5 at [Zn]/[GSH] = 0.01–2.0. SRNOM peak significantly overlapped with GSH peak at pH 8.0 and [SRNOM] > 1 mg L^?1 but was clearly separated from the GSH peak at pH 2.5. However, at pH 2.5, the presence of metal ions and/or SRNOM significantly underestimated GSH concentration (recovery = 21–69%), likely due to metal complexation with GSH and/or SRNOM adsorption onto Hg electrode. The effects of metal ions were minimised by the addition of EDTA. The interference induced by SRNOM adsorption was reduced as the [SRNOM] was reduced to 1 mg L^?1 and the recovery was improved to 98%.     

Calibrationless determination of cadmium, lead and copper in rain samples by stripping voltammetry at mercury microelectrodes: Effect of natural convection on the deposition step

Mercury microelectrodes were prepared by ex situ deposition of Hg onto Pt microdiscs. By exploiting the known properties of microelectrodes in stripping analysis, an absolute method based on a simple equation derived from the stripping charge and the microelectrode steady-state current was assessed for the simultaneous quantification of Cd²⁺, Pb²⁺ and Cu²⁺ concentrations. The method was tested with synthetic solutions containing known amounts of Cd²⁺, Pb²⁺ and Cu²⁺. Then, it was used to determine the labile and total fractions of these metal ions in rain samples. The labile fractions were measured from samples at their natural pH while the total concentrations were determined from samples at pH=2.     

Simultaneous Detection of Heavy Metals by Anodic Stripping Voltammetry Using Carbon Nanotube Thread

Carbon nanotube (CNT) threads are a type of CNT arrays that consist of super long CNTs. CNT threads inherit the advantages of CNTs, while avoiding the potential toxicity caused by individual CNTs. Electrodes based on CNT threads were fabricated and used for simultaneous detection of trace levels of Cu²⁺, Pb²⁺ Cd²⁺ and Zn²⁺ by anodic stripping voltammetry (ASV). The detection limits are 0.27 nM, 1.5 nM, 1.9 nM and 1.4 nM for Cu^2+, Pb²⁺, Cd²⁺ and Zn²⁺, respectively, in 0.1 M acetate buffer pH 4.5. The CNT thread electrode gives well‐defined, reproducible and sharp stripping signals for individual and simultaneous detection of heavy metals.     

The Fabrication and Characterization of a Bismuth Nanoparticle Modified Boron Doped Diamond Electrode and Its Application to the Simultaneous Determination of Cadmium(II) And Lead(II)

We report the simultaneous electroanalytical determination of Pb²⁺ and Cd²⁺ by square‐wave anodic stripping voltammetry (SWASV) using a bismuth nanoparticle modified boron doped diamond (Bi‐BDD) electrode. Bi deposition was performed in situ with the analytes, from a solution of 0.1 mM Bi(NO₃)₃ in 0.1 M HClO₄ (pH 1.2), and gave detection limits of 1.9 μg L^?1 and 2.3 μg L^?1 for Pb(II) and Cd(II) respectively. Pb²⁺ and Cd²⁺ could not be detected simultaneously at a bare BDD electrode, whilst on a bulk Bi macro electrode (BiBE) the limits of detection for the simultaneous determination of Pb²⁺ and Cd²⁺ were ca. ten times higher.     

Vibrational and scanning electron microscopy study of the mordenite modified by Mn, Co, Ni, Cu, Zn and Cd

The mordenite samples loaded with divalent nitrates of Mn, Co, Ni, Cu, Zn and Cd were investigated using FTIR and scanning electron microscopy (SEM) methods. It was found from FTIR spectra that in 3000-4000 cm⁻¹ region of mordenite samples with similar water concentration ions, Mn²⁺, Co²⁺, Cu²⁺, and Zn²⁺ tend to break hydrogen bonds formed between water molecules and zeolite framework, whereas Ni²⁺ and Cd²⁺ accommodate to hydrogen bonds. From SEM results it was concluded, that ions Mn²⁺, Co²⁺, Zn²⁺ form innersphere complexes with oxygens from Brönsted acid sites, whereas Ni²⁺ and Cd²⁺ associate with Brönsted acid sites without exchange of protons.     

Interfering influence of silver on the voltammetric behaviour of Cd2+ and Zn2+ ions on hmde in supporting electrolytes containing nitrates

A new kind of secondarily formed peaks was found in cyclic and stripping voltammetry in neutral sulphate, perchlorate and nitrate supporting electrolytes containing some divalent cations and a substance (for example O₂), the reduction of which gives as a by-product OH^? ions. The hydroxides deposited in the vicinity of the mercury electrode, in the course of a cathodic scan, react during the anodic scan according to the reaction Hg+Me(OH)₂=Hg(OH)₂+Me²⁺+2e forming a new, separate anodic peak.It was found that silver exerts a catalytic effect on the reduction of NO₃^? ions on the mercury electrode. In neutral nitrate supporting electrolyte containing Ag⁺ ions the hydroxides of some cations (Cd²⁺, Zn²⁺, Mn²⁺, Co²⁺ and Ni²⁺) were deposited during the cathodic scan or during the preelectrolysis. Afterwards, in the course of the anodic scan, a new peak, of the kind described above, was observed. The same effect was formerly interpreted, for Zn²⁺ and Cd²⁺, as evidence for the formation of intermetallic compounds, AgZn and AgCd.     

speciation of Cadmium(II) Using Donnan Dialysis and Differential-Pulse Anodic Stripping Voltammetry in a Flow-Injection System

Abstract

A flow-injection/Donnan dialysis/differential pulse anodic stripping voltammetry system was developed for the determination of free cadmium concentrations, [Cd²⁺], in solutions containing organically complexed Cd(II). A small dialysis cell with a strong cation-exchange membrane separating the sample and the receiver channels, was equilibrated in a flow-injection system. The ionic strength of sample and receiver solutions was 0.1 M, with NaNO₃ as the bulk electrolyte. By determining a constant fraction of the Cd²⁺ associated with the membrane phase, [Cd²⁺] of the samples could be measured.

Experimentally determined [Cd²⁺] corresponded well with those calculated, using tabulated stability constants, when citric acid, nitrilotriacetic acid, and oxalic acid were added as ligands. Thus, negatively charged and uncharged complexes were excluded from the membrane. Using the experimental design presented, [Cd²⁺]>5 × 10^×8 M could be determined, but there is a great potential for increasing the sensitivity of the method.

In solutions containing 1.0 μM Cd(II) and 200 mg fulvic acid/l, the inorganic fraction (Cd²⁺ CdNO₃ ⁺ decreased from 57% to 10% when the pH increased from 4.04 to 5.51. In a soil solution from an orthic podzol, having a high concentration of dissolved organic carbon (22.4 mM), the inorganic fraction constituted 53% of the total Cd(II) concentration.     

Cadmium(II) specifically interacts with cellular signaling to induce proto-oncogenes c-fos and c-jun in rat PC12 cells

Cadmium(II) compounds are carcinogens but only weakly mutagens. Because Cd(II) at low micromolar concentrations stimulates cell growth and induces some proto-oncogenes with several mammalian cell lines, the stimulation of cell proliferation is discussed as a major mechanism of the carcinogenicity of this metal. In the present work, the induction of the cellular proto-oncogenes c-fos and c-jun by Cd(II) was studied in rat PC12 cells. Several cellular signal transduction elements were tested as mediators of the proto-oncogene induction by cadmium. Cd(II) does not evoke mobilization of free intracellular Ca²⁺ in PC12 cells, and there was no impairment of the effect of Cd(II) by inhibitors of protein kinase A or of MAPK kinase. However, bisindolylmaleimide I, a specific inhibitor of protein kinase C abolished the proto-oncogene induction by Cd(II). Hence, a critical role for protein kinase C in the mitogenic effect of Cd(II) is inferred, and a substitution of structural Zn²⁺ ions by Cd²⁺ ions in this enzyme is discussed as the putative mechanism. Received: 30 July 1997 / Revised: 9 October 1997 / Accepted: 11 October 1997     

Cadmium(II) specifically interacts with cellular signaling to induce proto-oncogenes c-fos and c-jun in rat PC12 cells

Cadmium(II) compounds are carcinogens but only weakly mutagens. Because Cd(II) at low micromolar concentrations stimulates cell growth and induces some proto-oncogenes with several mammalian cell lines, the stimulation of cell proliferation is discussed as a major mechanism of the carcinogenicity of this metal. In the present work, the induction of the cellular proto-oncogenes c-fos and c-jun by Cd(II) was studied in rat PC12 cells. Several cellular signal transduction elements were tested as mediators of the proto-oncogene induction by cadmium. Cd(II) does not evoke mobilization of free intracellular Ca²⁺ in PC12 cells, and there was no impairment of the effect of Cd(II) by inhibitors of protein kinase A or of MAPK kinase. However, bisindolylmaleimide I, a specific inhibitor of protein kinase C abolished the proto-oncogene induction by Cd(II). Hence, a critical role for protein kinase C in the mitogenic effect of Cd(II) is inferred, and a substitution of structural Zn²⁺ ions by Cd²⁺ ions in this enzyme is discussed as the putative mechanism. Received: 30 July 1997 / Revised: 9 October 1997 / Accepted: 11 October 1997     

Non-conductive nanomaterial enhanced electrochemical response in stripping voltammetry: The use of nanostructured magnesium silicate hollow spheres for heavy metal ions detection

Nanostructured magnesium silicate hollow spheres, one kind of non-conductive nanomaterials, were used in heavy metal ions (HMIs) detection with enhanced performance for the first time. The detailed study of the enhancing electrochemical response in stripping voltammetry for simultaneous detection of ultratrace Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ was described. Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. The anodic stripping voltammetric performance toward HMIs was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detection limits achieved (0.186 nM, 0.247 nM, 0.169 nM and 0.375 nM for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺) are much lower than the guideline values in drinking water given by the World Health Organization (WHO). In addition, the interference and stability of the modified electrode were also investigated under the optimized conditions. An interesting phenomenon of mutual interference between different metal ions was observed. Most importantly, the sensitivity of Pb²⁺ increased in the presence of certain concentrations of other metal ions, such as Cd²⁺, Cu²⁺ and Hg²⁺ both individually and simultaneously. The proposed electrochemical sensing method is thus expected to open new opportunities to broaden the use of SWASV in analysis for detecting HMIs in the environment.     

The electrochemical stripping determination of tin in aqueous and nonaqueous media after its extraction

The anodic stripping voltammetric and chronopotentiometric determination of tin(IV) in aqueous and nonaqueous medium after its extraction using the rotating disc electrode made of glassy carbon with the mercury film was studied. The optimum composition of nonaqueous medium for the determination of tin is 0.2 M NaBr+5×10^?5M Hg²⁺ in 20 ml of the extract +30 ml of methanol. Tin(IV) was determined by anodic stripping voltammetry or chronopotentiometry down to the concentration 10^?7M. The selective determination of tin was studied. 10^?6M of tin(IV) was determined with an error ±4–5% even in the presence of metals: Co²⁺, Ni²⁺, Cd²⁺, Zn²⁺ (5×10^?3M), Ag⁺ and Pb²⁺ (5×10^?4M), Cu²⁺ (1.5×10^?4M), Sb³⁺ and Bi³⁺ (5×10^?5M).     

Synthesis and structure of enaminoketones of pyrazole containing 2-thione(selenone)benzimidazolyl fragments and their zinc and cadmium complexes

New ligand systems based on 4-formyl-5-hydroxypyrazole and 1-aminobenzimidazole derivatives are synthesized. The obtained enamines and their Zn²⁺ and Cd²⁺ metal complexes of composition ML₂ were investigated using the IR, heteronuclear (¹H, ¹³C, ¹⁵N, ⁷⁷Se, ¹¹³Cd) and two-dimensional NMR spectroscopy (COSY, HSQC, HMBC). The data of physicochemical investigations and quantum-chemical calculations showed that the ligands exist in the ketoamine tautomeric form. Quantum-chemical simulation of Zn(II) and Cd(II) complexes showed that the zinc complexes adopt the pseudo-tetrahedral and the cadmium complexes pseudo-octahedral configuration.     

Selective separations by reactive ion exchange: Part 4. Preconcentration of cadmium and zinc by in situ precipitation as hexacyanoferrate(II) salts on gel and macroporous ion-exchange resins

The in situ precipitation of traces of cadmium(II) and zinc(II) ions as hexacyanoferrates from aqueous matrices was studied on conventional polystyrene gel and macroporous cation- and anion-exchange resins. Coprecipitation with each other or with copper(II) ions present in binary cation resins or in solution, and the influence of added nonprecipitating ions of the same charge type such as magnesium(II) were investigated. Microporous (gel) cation exchangers gave reasonable recoveries and macroporous cation exchangers gave very good recoveries; but macroporous anion exchangers performed best, suggesting macroporous hexacyanoferrate(II) resin as an ideal phase for collection/preconcentration of traces of Cu²⁺, Cd²⁺, Zn²⁺, and possibly Co²⁺, Ni²⁺, and Pb²⁺ from waters. As expected, very low yields were obtained with conventional anion exchange resin in the hexacyanoferrate form. Uniform distribution of Cu²⁺, Zn²⁺, and Cd²⁺ over macroporous anion-exchange resin phases were established by means of electron probe scans and taken as evidence for the formation of a uniform, well-developed precipitate layer covering the entire resin particle surface.