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Constant M.g. Van Den Berg - One of the best experts on this subject based on the ideXlab platform.

  • arsenic speciation in natural waters by Cathodic Stripping Voltammetry
    Analytica Chimica Acta, 2010
    Co-Authors: Kristoff Gibbonwalsh, Pascal Salaun, Constant M.g. Van Den Berg
    Abstract:

    Abstract Contamination of groundwater with arsenic (As) is a major health risk through contamination of drinking and irrigation water supplies. In geochemically reducing conditions As is mostly present as As(III), its most toxic species. Various methods exist to determine As in water but these are not suitable for monitoring arsenic speciation at its original pH and without preparation. We present a method that uses Cathodic Stripping Voltammetry (CSV) to determine reactive As(III) at a vibrating, gold, microwire electrode. The As(III) is detected after adsorptive deposition of As(OH) 3 0 , followed by a potential scan to measure the reduction current from As(III) to As(0). The method is suitable for waters of pH 7–12, has an analytical range of 1 nM to 100 μM As (0.07–7500 ppb) and a limit of detection of 0.5 nM with a 60 s deposition time. The As speciation protocol involves measuring reactive As(III) by CSV at the original pH and acidification to pH 1 to determine inorganic As(III) + As(V) by anodic Stripping Voltammetry (ASV) using the same electrode. Total dissolved As is determined by ASV after UV-digestion at pH 1. The method was successfully tested on various raw groundwater samples from boreholes in the UK and West Bengal.

  • chemical speciation of iron in seawater by Cathodic Stripping Voltammetry with dihydroxynaphthalene
    Analytical Chemistry, 2006
    Co-Authors: Constant M.g. Van Den Berg
    Abstract:

    The chemical speciation of iron in seawater is determined by Cathodic Stripping Voltammetry using 2,3-dihydroxynaphthalene (DHN) as adsorptive and competing ligand. The optimized conditions include a DHN concentration of 0.5−1 μM, seawater at its original pH of 8, and equilibration overnight. The α-coefficient for DHN (=[FeDHN]/[Fe‘]) was calibrated against EDTA giving values of 166 for 0.5 μM DHN and 366 at 1 μM DHN and a value of 8.51 ± 0.07 for log K‘Fe‘DHN. The dissociation of the natural iron species FeL was found to have a characteristic reaction time of 50 min, indicating that titrations should be equilibrated overnight rather than the shorter periods sometimes used onboard ship. The method was applied to samples from the Pacific giving ligand concentrations of 1.1 and 1.6 nM for deep and surface waters, respectively, with an average value for log K‘FeL of 11.9 ± 0.3 compared to a value of 11.5 for the siderophore deferoxamine. The results are similar to those obtained previously for similar sample...

  • Determination of pyrithione in natural waters by Cathodic Stripping Voltammetry
    Analytica Chimica Acta, 2004
    Co-Authors: Doug S Mackie, Constant M.g. Van Den Berg, James W. Readman
    Abstract:

    Abstract A method was developed to determine the biocide pyrithione in natural waters. The method is based on Cathodic Stripping Voltammetry (CSV) in the presence of Triton-X-100, which is used to separate the peak from interfering thiol compounds. Optimised conditions include a Triton-X-100 concentration of 4 ppm and a pH adjusted to 9 using ammonia buffer. The adsorption potential for pyrithione was −0.10 V and the peak occurred at −0.2 to −0.3 V. Detection was by differential-pulse CSV. The detection limit in UV-digested seawater was 1.5 nM for a deposition time of 60 s. In principle, this limit of detection could be lowered by extending the adsorption time, but in practice this may not be possible due to interferences by other organic compounds (surfactants and thiol compounds) in natural waters.

  • Determination of Picomolar Levels of Iron in Seawater Using Catalytic Cathodic Stripping Voltammetry
    Analytical chemistry, 2001
    Co-Authors: Hajime Obata And, Constant M.g. Van Den Berg
    Abstract:

    A new procedure for the direct determination of picomolar levels of iron in seawater is presented. Cathodic Stripping Voltammetry (CSV) is preceded by adsorptive accumulation of the iron(III)−2,3-dihydroxynaphthalene (DHN) complex from seawater, containing 20 μM DHN at pH 8.0, onto a static mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is catalytically enhanced by the presence of 20 mM bromate. Optimized conditions include a 60-s adsorption period at −0.1 V and a voltammetric scan using sampled dc modulation at 10 Hz. In these conditions, a detection limit of 13 pM iron in seawater was achieved which can be lowered further by extending the adsorption time to 300 s. The new catalytic CSV method is ∼5 times more sensitive than existing CSV methods and was tested on samples from the Atlantic Ocean.

  • Determination of selenium by catalytic Cathodic Stripping Voltammetry.
    Analytica Chimica Acta, 2000
    Co-Authors: Britta Lange, Constant M.g. Van Den Berg
    Abstract:

    A procedure is described for the determination of selenium in natural waters using Cathodic Stripping Voltammetry in the presence of rhodium. Advantage is taken from a catalytic effect on the electrochemical reduction of protons in the presence of a mixed complex of selenide with rhodium and chloride, containing Cl‐Rh‐SeH species. The catalysis causes a very large peak-current at a negative peak potential for low (picomolar) selenium concentrations, close to the hydrogen wave. In addition to the selenium concentration, the peak height depends on the concentrations of acid (H C ) and chloride, and suffers from strong interference by organic surfactants. Optimised conditions include 0.3 M HCl, 75 ppb Rh(III) and a deposition potential of 0.2 V. UV-digestion was used to eliminate the interference caused by organic material and to convert Se(VI) to Se(IV). A3 detection limit of 2.4 pM Se(IV) was calculated from the standard deviation of a low selenium concentration (17 pM) using a deposition time of 50 s. © 2000 Elsevier Science B.V. All rights reserved.

Marko Branica - One of the best experts on this subject based on the ideXlab platform.

  • Square-wave Cathodic Stripping Voltammetry of hydrolyzed uranyl species
    Analytica Chimica Acta, 1995
    Co-Authors: Renata Djogić, Marko Branica
    Abstract:

    Abstract Adsorption of uranyl-hydroxo species has been studied using square-wave Cathodic Stripping Voltammetry (SWCSV). The peak of the uranyl ion between pH 5 and 8 has the characteristic features of a reduction complicated with reactant adsorption. The reduction process is totally irreversible, with an average transfer coefficient α = 0.47. The adsorbed species was found to be most probably UO 2 (OH) 0 2 , after correlation of the experimental results with the calculated ionic distribution in the solution. The experimental conditions for the lowest detection limit are given and it amounts to 2 × 10 −8 mol l −1 of uranyl hydroxo species. The maximum surface concentration is determined, to be Γ = (2.6 ± 0.1) × 10 −10 mol cm −2 .

  • Direct determination of dissolved uranyl(VI) in sea-water by Cathodic Stripping Voltammetry
    The Analyst, 1995
    Co-Authors: Renata Djogić, Marko Branica
    Abstract:

    The effect of the adsorption of uranyl species on the static mercury drop electrode is used for the electrochemical determination of dissolved uranium concentration in untreated and estuarine sea-water. The measurements were performed by square-wave Cathodic Stripping Voltammetry. The standard additions method is successfully applied for measurements of natural uranyl concentrations in water samples which were found to be in the range between 4.3 and 15 nmol l–1 depending on the sampling location with detection limits of 2.4 and 10 nmol l–1, respectively.

  • Cathodic Stripping Voltammetry of the copper–1,10‐phenanthroline complex
    Electroanalysis, 1995
    Co-Authors: Ivan Čuljak, Marina Mlakar, Marko Branica
    Abstract:

    Cathodic Stripping Voltammetry of copper, based on the accumulation and reduction of its complex with 1,10-phenanthroline (phen), has been studied. The complex is reduced in two steps from CuI–phen and CuII–phen to copper amalgam at potentials of −0.43 and −0.62 V vs. Ag/AgCl, respectively. The reduction processes are strongly dependent on the pH of the solution, as well as on the concentration of the metal ion and ligand. The reduction mechanism of both complexes was established. The detection limit for copper in 0.55 mol/LNaCl with 20 min accumulation at 0.0 V vs. Ag/AgCl, measuring the reduction peak of the CuI–phen complex at −0.43 V vs. Ag/AgCl by SWV, was found to be about 5 × 10−10 mol/L. The reaction parameters were calculated by square-wave Voltammetry (SWV), i.e., transfer coefficients α = 0.31 and α = 0.45, and the maximum surface concentrations Γ = (2.02 ± 0.08) × 10−11 mol/cm2 and Γ = (2.83 ± 0.12) × 10−12 mol/cm2. Measurements of the copper content in natural seawater samples were performed as well.

Tatsuhiko Tanaka - One of the best experts on this subject based on the ideXlab platform.

  • Cathodic Stripping Voltammetry of Selenium(IV) at a Silver Disk Electrode.
    Analytical chemistry, 1996
    Co-Authors: Takashi Ishiyama, Tatsuhiko Tanaka
    Abstract:

    A new, simple, and reproducible method is described for the determination of selenium(IV) based on differential pulse Cathodic Stripping Voltammetry. The optimized experimental conditions are as follows:  selenium(IV) ions in an acidic medium (0.06 M HCl−0.07 M HNO3) are electrodeposited on a rotating silver disk electrode as silver selenide at −0.4 V vs SCE for 30 min; the deposit is then Cathodically stripped in another solution (2 M NaOH) at a scan rate of 50 mV s-1 to −1.2 V vs SCE. The Cathodic Stripping results in only a single well-defined peak at about −0.95 V vs SCE. The calibration (peak height vs selenium concentration) graph is linear up to at least 40 ng mL-1 of selenium(IV) and passes through the origin, with a relative standard deviation of 2.7% for 20 ng mL-1 (n = 5). The detection limit (3σ) is 0.20 ng mL-1. The possible interferences have been evaluated. Dissolved oxygen does not affect the peak height of selenium. The electrode can be used repeatedly at least 20 times with excellent rep...

Renata Djogić - One of the best experts on this subject based on the ideXlab platform.

  • Square-wave Cathodic Stripping Voltammetry of hydrolyzed uranyl species
    Analytica Chimica Acta, 1995
    Co-Authors: Renata Djogić, Marko Branica
    Abstract:

    Abstract Adsorption of uranyl-hydroxo species has been studied using square-wave Cathodic Stripping Voltammetry (SWCSV). The peak of the uranyl ion between pH 5 and 8 has the characteristic features of a reduction complicated with reactant adsorption. The reduction process is totally irreversible, with an average transfer coefficient α = 0.47. The adsorbed species was found to be most probably UO 2 (OH) 0 2 , after correlation of the experimental results with the calculated ionic distribution in the solution. The experimental conditions for the lowest detection limit are given and it amounts to 2 × 10 −8 mol l −1 of uranyl hydroxo species. The maximum surface concentration is determined, to be Γ = (2.6 ± 0.1) × 10 −10 mol cm −2 .

  • Direct determination of dissolved uranyl(VI) in sea-water by Cathodic Stripping Voltammetry
    The Analyst, 1995
    Co-Authors: Renata Djogić, Marko Branica
    Abstract:

    The effect of the adsorption of uranyl species on the static mercury drop electrode is used for the electrochemical determination of dissolved uranium concentration in untreated and estuarine sea-water. The measurements were performed by square-wave Cathodic Stripping Voltammetry. The standard additions method is successfully applied for measurements of natural uranyl concentrations in water samples which were found to be in the range between 4.3 and 15 nmol l–1 depending on the sampling location with detection limits of 2.4 and 10 nmol l–1, respectively.

Takashi Ishiyama - One of the best experts on this subject based on the ideXlab platform.

  • Cathodic Stripping Voltammetry of Selenium(IV) at a Silver Disk Electrode.
    Analytical chemistry, 1996
    Co-Authors: Takashi Ishiyama, Tatsuhiko Tanaka
    Abstract:

    A new, simple, and reproducible method is described for the determination of selenium(IV) based on differential pulse Cathodic Stripping Voltammetry. The optimized experimental conditions are as follows:  selenium(IV) ions in an acidic medium (0.06 M HCl−0.07 M HNO3) are electrodeposited on a rotating silver disk electrode as silver selenide at −0.4 V vs SCE for 30 min; the deposit is then Cathodically stripped in another solution (2 M NaOH) at a scan rate of 50 mV s-1 to −1.2 V vs SCE. The Cathodic Stripping results in only a single well-defined peak at about −0.95 V vs SCE. The calibration (peak height vs selenium concentration) graph is linear up to at least 40 ng mL-1 of selenium(IV) and passes through the origin, with a relative standard deviation of 2.7% for 20 ng mL-1 (n = 5). The detection limit (3σ) is 0.20 ng mL-1. The possible interferences have been evaluated. Dissolved oxygen does not affect the peak height of selenium. The electrode can be used repeatedly at least 20 times with excellent rep...