Cadmium(II) binding by soil-derived fulvic acid measured by anodic stripping voltammetry

Titrations of aqueous solutions of soil fulvic acid (30, 45, and 60 mg l^-1) with cadmium ion solutions at pH 6 and 7 reveal unusual shapes in the stripping current (i_s) vs. total cadmium ion (C_cd²⁺) curves. The expected inflections occur in the titration curves at 8–16 μM. at pH 6 and 12–26 μM at pH 7. In addition, there is an initial rapid increase in i_s at very low C_cd²⁺. The initial rapid increase in current is attributed to labile cadmium—fulvic acid complexes that contribute to i_s by rapid dissociation. Subsequent addition of cadmium ion results in moderately labile complexes and i_s becomes partially kinetically controlled. The stripping current was corrected for kinetic current contributions from dissociation of complexes, and total ligand concentrations, conditional stability constants, and upper slopes were calculated from data well past the titration end-point. The use of upper slopes after kinetic current corrections as in situ calibration curves, allowed calculations of equilibrium cadmium concentrations. The data show that both kinetic current corrections and in situ calibration curves are necessary to avoid substantial errors in calculations of equilibrium cadmium concentrations from anodic stripping voltammetric experiments.     

Thermal studies of cobalt(II), nickel(II) and copper(II) 3-substituted-4-salicylideneamino-5-mercapto-1,2,4-triazole complexes

Complexes of Co^II, Ni^II and Cu^II with 3-substituted-4-salicylideneamino-5-mercapto-1,2,4-triazole have been prepared and characterized by elemental analysis, electronic, i.r., e.s.r. and t.g. studies. T.g. studies show that the complexes thermally degrade in two steps. Kinetic and thermodynamic parameters were computed from the thermal decomposition data. The activation energies of both the thermal degradation steps lie in the 0.24–42.67 kJ mol⁻¹ range. This revised version was published online in June 2006 with corrections to the Cover Date.     

Continuous flow and flow injection stripping voltammetric determination of silver(I), mercury(II), and bismuth(III) at a bulk modified graphite tube electrode

The epoxy-impregnated graphite tube electrode bulk modified with 2-mercaptobenzoxazole, employed in a wall-jet configuration, was found to be useful for the continuous flow and flow injection stripping voltammetric determinations of Ag^I, Hg^II and Bi^III. For continuous flow, detection limits for Ag^I, Hg^II and Bi^III were 1.8 × 10⁻¹⁰ M, 1.9 × 10⁻⁹ M and 9.5 × 10⁻⁹ M, respectively (10 min accumulation, S/N = 3). Precisions for 5.00 × 10⁻⁹ M Ag^I, 1.00 × 10⁻⁸ M Hg^II and 1.00 × 10⁻⁷ M Bi^III were 10.5%, 5.77 % and 7.90% (relative standard deviations, n = 6), respectively. In the case of flow injection stripping, with a 500 μL injection loop, detection limits of 0.59 ng, 2.0 ng and 120 ng were obtained for Ag^I, Hg^II and Bi^III, respectively (S/N = 3). Selected metal ions, inorganic and organic substances were investigated for interferences. The electrode was tested with a certified sample and then applied to the determinations of the metal ions in a urine and a sea-water sample.     

Application of sampled-d.c. anodic stripping voltammetry to metal/fulvic acid equilibria

The use of anodic stripping voltammetry (ASV) to determine the labile metal fraction in metal/ fulvic acid equilibrium systems is discussed. A method is described for distinguishing between the contributions of processes in the reduction and oxidation steps to the observed anodic (stripping) current. This method, which facilitates separate examination of the two processes, is based on timed addition of fulvic acids during the deposition step, on pH control, and on measurement of sampled-d.c. ASV peak areas (Faradaic charge) for metal/fulvic acid solutions. Results are presented for copper(Il) and lead(Il) complexes with six colloid-free soil-derived fulvic acids. In contrast to differential-pulse ASV, the stripping current measured by sampled-d.c. ASV showed no measurable contribution from ligand adsorption on the mercury drop. For heterogeneous ligand systems, such as fulvic acid, use of stripping peak heights over-estimates the fraction of non-labile metal complex because peak broadening results from the range of complexes formed in the anodic step.     

Carbon-fiber microsensor for in vivo monitoring of trace zinc(II) based on electrochemical stripping analysis

The optimization and characterization of a microsensor for trace zinc based on stripping voltammetry at a single carbon-fiber microelectrode are reported. Despite the absence of a mercury coverage, the carbon-fiber stripping sensor displays a significant hydrogen overvoltage in the physiological pH and a well-defined zinc stripping peak (at ca. −1.17 V). 5 s deposition periods allow convenient quantitation of zinc over the 100–1000 ng/ml (ppb) range. Detection limits of 0.8 ng/ml (1.2×10⁻⁸ M) and 20 ng/ml (3.0×10⁻⁷ M) zinc were estimated in connection to 60 and 1 s deposition, respectively. The response is reversible with the stripping/measurement step completely removing the accumulated zinc. Measurement frequencies as high as 30 runs per min can thus be realized (in connection to 1 s deposition and measurement steps). The influence of relevant variables of the deposition and stripping steps is examined. The attractive behavior of the stripping-voltammetric microsensor offers great promise for in vivo monitoring of trace levels of zinc.     

New complexes of iron(III), cobalt(II), nickel(II) and copper(II) with Schiff bases derived from 2-aminocyclopent-1-ene-1-dithiocarboxylic acid

Summary Fe^III, Co^II, Ni^II and Cu^II, complexes of a new Schiff base ligand, prepared by condensing 2-aminocyclopent-1-ene-1-dithiocarboxylic acid with benzaldehyde (ACB), and also Cu^II and Ni^II complexes of a second Schiff base ligand prepared by condensing 2-aminocyclopent-1-ene-1-dithiocarboxylic acid with salicylaldehyde (ACS), have been prepared and characterized by elemental analyses, conductivity measurements, magnetic and spectral (electronic, i.r. and e.p.r.) studies. The i.r. spectra suggest that both ACB and ACS are acting as bidentate ligands, coordinating through one of the sulphur atoms and through the azomethine nitrogen atom. The magnetic moment of the Fe^III complex indicates spin crossover behaviour. Square planar structures have been assigned to the Cu^II and Ni^II complexes and a tetrahedral structure to the Co^II complex. The e.p.r. spectra of the Cu^II complexes suggest a square planar environment with rhombic distortion around the Cu^II ion.     

Structural studies on cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) complexes of 1-malonyl-bis(4-phenylthiosemicarbazide)

Summary Several new complexes of the title ligand (H₂MPTS) with Co^II, Ni^II, Cu^II, and Cd^II have been prepared. Structural assignments of the complexes have been made based on elemental analysis, molar conductivity, magnetic moment and spectral (i.r.,¹H n.m.r., reflectance) studies. The compounds are non-conductors in dimethylsulphoxide. The neutral molecule is coordinated to the metal(II) sulphate as a bidentate ligandvia the two carbonyl groups. The ligand reacts with the metal(II) chlorides with the liberation of two hydrogen ions, behaving as a bianionic quadridentate (NONO) donor. Enolization is confirmed by the pH-titration of H₂ MPTS and its metal(II) complexes against NaOH. A distorted octahedral structure is proposed for the Cu^II complex, while a square planar structure is suggested for both Co^II and Ni^II complexes. The stoichiometry of the complexes formed in EtOH and buffer solutions, their apparent formation constants and the ranges for obedience to Beer's law are reported for Co^II, Ni^II and Cu^II ions. The ligand pK values are calculated. The antimicrobial activity of H₂ MPTS and its Co^II, Ni^II, Cu^II and Mn^II complexes is demonstrated.     

Novel five- and six-coordinate zinc (II), cadmium (II) and mercury(II) complexes of macrocyclic ligands

Summary Complexes of 2,6-dipicolinic acid hydrazide, DPH, with Zn^II, Cd^II and Hg^II have been prepared and characterized by elemental analysis, i.r. and electronic spectra and by electrical conductance measurements. The ligand is terdentate, having coordination sites at two deprotonated amide-nitrogen and pyridine-nitrogen atoms. The Zn^II and Hg^II complexes are pentacoordinate whereas the Cd^II complexes are hexacoordinate and have trigonal bipyramidal and pseudooctahedral stereochemistries, respectively. The Zn, Cd and Hg ions induce cyclization of DPH complexes upon reaction with-diketones. The complexes of macrocyclic ligands so formed have the same stereochemistries as those of DPH.     

Cathodic stripping voltammetry and adsorptive stripping voltammetry of selenium(IV)

Cathodic stripping voltammetry of selenium(IV) in 0.1 M hydrochloric acid media yielded a nonlinear calibration graph for the concentration range 10^?9?10^?8 M. In this concentration range, adsorptive stripping voltammetry based on adsorption of the selenium/3,3′-diaminobenzidine complex on the surface of the hanging mercury drop electrode at the deposition potential of +0.05 V (vs. SCE) is more convenient. A linear calibration graph is obtained for selenium concentrations of 3×10^?9?3×10?8 M, with an accumulation time of 300 s.     

Water hyacinth modified carbon paste electrode for simultaneous electrochemical stripping analysis of Cd (II) and Pb (II)

In this study, we demonstrated a highly sensitive electrochemical sensor for the simultaneous detection of Pb (II) and Cd (II) in aqueous solution using carbon paste electrode modified with Eichhornia crassipes powder by square wave anodic stripping voltammetry. The effect of modifier composition, pH, preconcentration time, reduction potential and time, and type of supporting electrolyte on the determination of metal ions were investigated. Pre-concentration on the modified surface was performed at open circuit. The modified electrode exhibited well-defined and separate stripping peaks for Pb (II) and Cd (II). Under optimum experimental conditions, a linear range for both metal ions was from 10 to 5000 μg L^?1 with the detection limits of 4.9 μg L^?1, 2.1 μg L^?1 for Cd(II) and Pb (II), respectively. The modified electrode was found to be sensitive and selective when applied to determine trace amounts of Cd (II) and Pb (II) in natural water samples.     

Effects of complexants and surfactants on the deposition and stripping steps in chronopotentiometric stripping analysis and anodic stripping voltammetry: implications for operationally defined speciation measurements

The influence of humic substances, Triton X-100 and red wine on the deposition and stripping steps in anodic stripping voltammetry and chronopotentiometric stripping analysis (CPSA) of Cu(II) and Pb(II) was investigated. Fulvic acid and Triton X-100 had an impact only on the stripping step; humic acid and red wine influenced both steps. Failure to establish the impact of matrix components on the individual deposition and stripping steps could result in erroneous interpretation of metal ion speciation.     

Flow potentiometric stripping analysis for mercury(II) in urine,sediment and acid digest of biological material

In flow potentiometric stripping analysis for mercury in urine, the samples are acidified with concentrated nitric acid and heated to boiling for 10 min. After cooling, the samples are buffered by the addition of concentrated ammonia and then pre-electrolysed at a gold working electrode for 90 s at -0.25 V vs. SCE at a flow rate of 1.75 ml min^-1. The stripping solution is 1 M sodium bromide solution acidified with 0.1 M hydrochloric acid and containing chromium(VI). The detection limit at one sigma level is 0.05 μM. Orchard leaves, sediment and fish muscles are digested in nitric acid at 140°C for 30 min prior to buffering with ammonia and potentiometric stripping analysis for 200 s at -0.20 V vs. SCE at a flow rate of 1.75 ml min^-1.     

Flow potentiometric stripping analysis for mercury(II)

The optimum experimental conditions, with respect to sample and stripping solution composition, in computerised flow potentiometric stripping analysis for mercury(II) with a gold working electrode are described. When pre-electrolysis -was done in a sample to which ammonia and iodide had been added and stripping was done in an acidified bromide solution containing chromium(VI), a detection limit of 2 nM (0.4 μg kg^-1) was obtained after 90 s of pre-electrolysis, the dynamic range being almost three decades. Copper(II) interfered when present in a 1000-fold excess and silver(I) when present in a 5-fold excess over mercury(II).     

Effect of mercury(II) on metal complex labilities determined by direct-current anodic stripping voltammetry on a thin mercury film electrode

The labilities of copper, lead and cadmium complexes with fulvic acid, nitrilotriacetic acid and an iron-humic acid colloid were studied on a preplated thin mercury film electrode and with in-situ plating of mercury on a glassy carbon electrode. In the presence of mercury(II) the apparent labilities based on direct-current anodic stripping voltammetric peak-area measurements increased for each of the cadmium and lead species and for the copper iron-humic acid colloid species. In contrast, for the copper complexes with nitrilotriacetic acid and fulvic acid the lability was not measurably altered by mercury(II); it is inferred that they do not undergo rapid metal exchange with mercury(II).     

N-acetyl-DL-leucinate cobalt(II), nickel(II) and zinc(II) complexes

Summary Complexes of the type M(AcLeu)₂ · B₂ (M = Co^II, Ni^II or Zn^II; B = H₂O, py, 3-pic, 4-pic; AcLeu =N-acetyl-DL-leucinate ion) and M(AcLeu)₂ B (M = Co^II or Zn^II and B = o-phen) were prepared and investigated by means of magnetic and spectroscopic measurements. The i.r. spectra of all the complexes are consistent with bidentate coordination of the amino acid to the metal ion. The room temperature solid state electronic spectra indicate that the symmetry of this species is closer toD _4h and that MO₆ and MO₄N₂ chromophores are present in the M(AcLeu)₂ · 2 H₂O and M(AcLeu)₂B_n · x H₂O (B = py, 3-pic, 4-pic, n=2 and x=0 for M = Ni^II; B = o-phen, n=1 and x=0 for M = Co^II; B = py, 3-pic, 4-pic, n=1 and x=1 for M = Co^II) complexes, respectively. By comparing the Dq values of the amino acid and those of other N-substituted amino acids previously studied, a spectrochemical series of the the cobalt(II) and nickel(II) complexes is proposed. The¹ H n.m.r. spectra of the zinc(II) complexes confirm the proposed stereochemistry.     

Kinetics of the complexation of manganese(II), cobalt(II) and zinc(II) with DL-isocitric acid

The kinetics of complexation of Mn^II, Co^II and Zn^II by isocitric acid have been studied by the stopped flow method at 15,25 and 35°C, ionic strength 0.20 M (NaClO₄) and pH range 4.50–6.35. Under these experimental conditions, one process is observed for each system within a few seconds. A mechanism is proposed to account for the observed behaviour, which is associated with participation of the OH group in complex formation. Activation energies are also reported. TMC 2593     

Chelated complexes of cadmium(II), cobalt(II), copper(II), mercury(II), nickel(II), uranyl(II) and zinc(II) with benzil bis(4-phenylthiosemicarbazone)

Summary Complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Hg^II and UO ₂ ^II with benzil bis(4-phenylthiosemicarbazone), H₂BPT, have been synthesized and their structures assigned based on elemental analysis, molar conductivity, magnetic susceptibility and spectroscopic measurements. The i.r. spectra suggest that the ligand behaves as a binegative quadridentate (NSSN) (Co^II, Cu^II, Hg^II and UO ₂ ^II complexes) or as a binegative quadridentate-neutral bidentate chelating agent (Ni^II, Zn^II and Cd^II complexes). Octahedral structures for the Co^II and Ni^II complexes and square-planar structure for the Cu^II complex are suggested on the basis of magnetic and spectral evidence. The crystal field parameters (Dq, B and _B) for the Co^II complex are calculated and agree fairly well with the values reported for known octahedral complexes. The ligand can be used for the microdetermination of Ni^II ions of concentration in the 0.4–6×10^–4 mol l^–1 range and the apparent formation constant for the species generated in solution has also been calculated.     

Selenium-coated carbon electrode for anodic stripping voltammetric determination of copper(II)

We describe a new and promising type of selenium film electrode for anodic stripping voltammetry. This method is based on formation of copper selenide onto an in-situ formed selenium-film carbon electrode, this followed by Osteryoung square-wave anodic stripping voltammetry. Copper(II) is also in-situ electroplated in a test solution containing 0.01 mol L^-1 hydrochloric acid, 0.05 mol L^?1 potassium chloride and 500 µg L^?1 Se(IV) at a deposition potential of ?300 mV. The well-defined anodic peak current observed at about 200 mV is directly proportional to the Cu(II) concentration over the range from 1.0 to 100 µg L^?1 under the optimized conditions. The detection limit (three sigma level) is 0.2 µg L^?1 Cu(II) at 180 s deposition time. Relatively less interferences are shown from most of metal ions except for antimony(III). The method can be applied to analyses of river water and oyster tissue with good accuracy.     

Interaction of manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) with acetylhydrazine, formed in situ; first crystal structure of tris(acetylhydrazine) nickel(II) perchlorate

A series of transition metal complexes of the type [M(ah)₃](ClO₄)₂ (1–6) [M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II and Zn^II, ah = acetylhydrazine] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with acetylhydrazine formed in situ by the reaction of hydrazine hydrate and acetylsalicylic acid methyl ester. The chelating behaviour of acetylhydrazine and overall geometry of these complexes have been spectroscopically investigated by means of FT-IR, ¹H-n.m.r. and electronic spectral techniques, as well as by elemental analysis data, molar conductance values and magnetic susceptibility measurements. Single X-ray structure determination of complex (4) revealed three acetylhydrazine ligands coordinated to nickel ion in a bidentate manner maintaining an octahedral environment. In all other complexes too, an octahedral geometry has been proposed on the basis of results obtained by various physico-chemical studies.     

Simultaneous determination of mercury(II), copper(II) and bismuth(III) in urine by flow constant-current stripping analysis with a gold fibre electrode

Urine samples are treated with concentrated nitric acid and potassium permanganate ar 70°C for 10 min prior to injection. The flow electrode system consists of a 10-μm diameter gold fibre working electrode, a glassy carbon reference electrode and a platinum counter electrode. In the fully automated constant-current stripping procedure, the gold fibre is first covered with a fresh gold film after which the sample is electrolyzed for 1 min prior to stripping in 0.1 M hydrochloric acid with a current of 0.1μA. The procedure is repeated on a spiked sample after which the sample analyte concentrations are evaluated and presented digitally and graphically on a printer/plotter. The results obtained for bismuth, copper and mercury in a urine reference sample were 36.9, 39.7 and 47.7 μg l^?1 with standard deviations (n=10) of 3.2, 4.2 and 2.1, respectively. The certified values for copper and mercury were 45 and 51 μg l^?1; no certified value was available for bismuth.