Page 1. Communications Gas Electrode Method for Determination of Azide in Aqueous Samples From th... more Page 1. Communications Gas Electrode Method for Determination of Azide in Aqueous Samples From the Reprocessing Industry Johannes T. van Elteren*†a, Constant MG van den Berga and Trevor D. Martinb a Oceanography ...
Page 1. Analyst, June 1994, Vol. 11 9 1349 Preconcentration of Chromium(iii) from Sea-water by Ad... more Page 1. Analyst, June 1994, Vol. 11 9 1349 Preconcentration of Chromium(iii) from Sea-water by Adsorption on Silica and Voltammetric Determination Marc Bowemart* and Constant M. G. van den Berg? Oceanography Laboratory, The University, Liverpool, UK L69 3BX ...
Borate anions, B(OH)(-)(4), are known to associate with alkali and alkaline-earth metal cations i... more Borate anions, B(OH)(-)(4), are known to associate with alkali and alkaline-earth metal cations in sea-water. The borate cation ion-pairs are of the general form MB(OH)((n-1)+)(4), where M(n+) is the cation. In this work, the cation borate stability constants (K*(MB)) have been evaluated for Na(+), Li(+), Mg(2+), Ca(2+) and Sr(2+) where K*(MB) = [MB(OH(4))((n-1)+)]/[M(n+)][B(OH)(-)(4)]. The K*(MB) values were obtained from values found for the stability constant of boric acid (K*(B)) in various electrolyte media at 25 degrees and an ionic strength of 0.7. Acid-base potentiometric titrations were performed in the electrolyte media with a standard Pt/H(2) electrode and a junctionless Ag/AgCl reference electrode to monitor the emf. A non-approximative equation was used to linearize the titration data. The values obtained were: K*(Lib) = 0.89 +/- 0.02, K*(NaB) = 0.44 +/- 0.01, K*(MgB) = 13.6 +/- 0.7, K*(CaB) = 11.4 +/- 0.15, K*(SrB) = 3.47 +/- 0.06. The values for K*(MB) correlate with the charge-density parameter z(2)/(r + 0.85), where r is the radius of the cation. The speciation of boron in sea-water was predicted from the K*(MB), data for the major cations present.
... of the stability constants of Fe–AL complexes. CLE/CSV of ligands in natural waters requires ... more ... of the stability constants of Fe–AL complexes. CLE/CSV of ligands in natural waters requires calibration of the complex stability of iron with the added competing ligand (α Fe′AL in Eq. 1, where α Fe′AL = K′ Fe′AL x[AL]). ...
... measurement. The detection limit of MnO2 is related to its concentration, number of adsorptio... more ... measurement. The detection limit of MnO2 is related to its concentration, number of adsorption sites, and the metal binding constant (van den Berg and Dharmvanij, 1984). In this case this is equivalent to a K'CL value of about 400. ...
Page 1. I шмиш ELSEVIER Marine Chemistry 59 (1998) 283-300 ===== Variability in the speciation of... more Page 1. I шмиш ELSEVIER Marine Chemistry 59 (1998) 283-300 ===== Variability in the speciation of iron in the northern North Sea Martha Gledhill a ', Constant MG van den Berg a*, Rob F. Nolting b, Klaas R. Timmermans ...
ABSTRACT Preliminary measurements of sulfide in seawater using cathodic stripping voltammetry and... more ABSTRACT Preliminary measurements of sulfide in seawater using cathodic stripping voltammetry and a hanging mercury drop electrode (HMDE) in batch-mode showed that the sulfide peak decreased rapidly with time. This decrease was not caused by O2, H2O2 or IO3−, and the sulfide peak was not stabilised by trace metal additions. A home-made flow-cell was constructed to enable the determination of sulfide in seawater using voltammetry with an HMDE. A stable sulfide peak was obtained by flow-analysis with voltammetric detection, with a precision of 2.8% and detection limit of 0.5 nM at a 60 s adsorption time. Several thiol compounds were found to produce a peak at, or very close to, the peak potential for sulfide. Their interference was evaluated by allowing the sulfide peak in conventional (batch) voltammetry to decay. Comparative experiments showed that waste metallic mercury is responsible for removal of sulfide in batch-mode analysis due to formation of insoluble mercuric sulfide salts causing the rapid decay of the sulfide peak. The problem is circumvented by using flow-analysis to determine sulfide.
Apparatus is designed and tested to determine metals in situ in seawater. Voltammetry with a vibr... more Apparatus is designed and tested to determine metals in situ in seawater. Voltammetry with a vibrating gold microwire electrode (VGME) is combined with a battery powered potentiostat and a processor board and is tested for in situ monitoring of copper (Cu) in coastal waters. The VGME was combined with solid state reference and counter electrodes to make a single vibrating probe which was rated up to a depth of 40 m. The measuring mode for Cu was square-wave anodic stripping voltammetry whilst dissolved oxygen (DO) was monitored by a linear sweep scan in a negative potential direction. The working electrode was reactivated between measurements using a suitable potential sequence. The novelties of this work are the field-testing of apparatus incorporating a VGME for copper monitoring, which eliminates the need for pumping and reagents, but has sufficient sensitivity for low ambient levels of copper, and the use of a novel potential sequence to stabilise the response over a long time period. The apparatus has a measuring time of about 6 weeks and a measuring frequency of 12 h(-1). Measurement is reagent-free and power use is low as no pump is required. Experiments are carried out to test the stability of response of the system at various temperatures and its robustness with respect to long-term copper monitoring. Preliminary data were obtained during autonomous deployment over several weeks on a buoy in the Irish Sea. Vertical movement of the buoy caused individual measurements to have a variability of about 15%. It was found that longer term variability of the electrode could be minimised by normalisation of the Cu response over that of DO as the response was related to diffusion through the electrode surface which was similarly affected. The detected fraction of Cu (labile Cu) amounted to 1.5-4 nM during different deployments at a total Cu concentration of ∼10 nM. The same ratio was found by voltammetry in samples taken to the laboratory. The new apparatus has demonstrated that metals in coastal waters can be monitored at trace level, much facilitating the monitoring of outfalls and local water contamination. Because of its sensitivity the apparatus would be of use in estuarine as well as coastal waters, with the aim of monitoring intermittent variability in the copper concentration.
International Journal of Environmental Analytical Chemistry, 1998
Intern. J. Envimn.A~l. Chem..Vol.l1(1),pp. 1-17 Reprints available directly from Ihe publisher Ph... more Intern. J. Envimn.A~l. Chem..Vol.l1(1),pp. 1-17 Reprints available directly from Ihe publisher Photocopying permitted by license only ... 0 1998 OPA (OvaMPs Publishers Association) Amsterdam NV Published by license under the Gordon and Breach Science P ublish imprint. Printed ...
Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry ... more Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry (CSV), is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV. This work presents the CSV method to determine As(III) in high-iron or -manganese groundwaters in the field with only minor sample treatment. The method was field-tested in West-Bengal (India) on a series of groundwater samples. Total arsenic was subsequently determined after acidification to pH 1 by anodic stripping voltammetry (ASV). Comparative measurements by ICP-MS as reference method for total As, and by HPLC for its speciation, were used to corroborate the field data in stored samples. Most of the arsenic (78±0.02%) was found to occur as inorganic As(III) in the freshly collected waters, in accordance with previous studies. The data shows that the modified on-site CSV met...
Page 1. Communications Gas Electrode Method for Determination of Azide in Aqueous Samples From th... more Page 1. Communications Gas Electrode Method for Determination of Azide in Aqueous Samples From the Reprocessing Industry Johannes T. van Elteren*†a, Constant MG van den Berga and Trevor D. Martinb a Oceanography ...
Page 1. Analyst, June 1994, Vol. 11 9 1349 Preconcentration of Chromium(iii) from Sea-water by Ad... more Page 1. Analyst, June 1994, Vol. 11 9 1349 Preconcentration of Chromium(iii) from Sea-water by Adsorption on Silica and Voltammetric Determination Marc Bowemart* and Constant M. G. van den Berg? Oceanography Laboratory, The University, Liverpool, UK L69 3BX ...
Borate anions, B(OH)(-)(4), are known to associate with alkali and alkaline-earth metal cations i... more Borate anions, B(OH)(-)(4), are known to associate with alkali and alkaline-earth metal cations in sea-water. The borate cation ion-pairs are of the general form MB(OH)((n-1)+)(4), where M(n+) is the cation. In this work, the cation borate stability constants (K*(MB)) have been evaluated for Na(+), Li(+), Mg(2+), Ca(2+) and Sr(2+) where K*(MB) = [MB(OH(4))((n-1)+)]/[M(n+)][B(OH)(-)(4)]. The K*(MB) values were obtained from values found for the stability constant of boric acid (K*(B)) in various electrolyte media at 25 degrees and an ionic strength of 0.7. Acid-base potentiometric titrations were performed in the electrolyte media with a standard Pt/H(2) electrode and a junctionless Ag/AgCl reference electrode to monitor the emf. A non-approximative equation was used to linearize the titration data. The values obtained were: K*(Lib) = 0.89 +/- 0.02, K*(NaB) = 0.44 +/- 0.01, K*(MgB) = 13.6 +/- 0.7, K*(CaB) = 11.4 +/- 0.15, K*(SrB) = 3.47 +/- 0.06. The values for K*(MB) correlate with the charge-density parameter z(2)/(r + 0.85), where r is the radius of the cation. The speciation of boron in sea-water was predicted from the K*(MB), data for the major cations present.
... of the stability constants of Fe–AL complexes. CLE/CSV of ligands in natural waters requires ... more ... of the stability constants of Fe–AL complexes. CLE/CSV of ligands in natural waters requires calibration of the complex stability of iron with the added competing ligand (α Fe′AL in Eq. 1, where α Fe′AL = K′ Fe′AL x[AL]). ...
... measurement. The detection limit of MnO2 is related to its concentration, number of adsorptio... more ... measurement. The detection limit of MnO2 is related to its concentration, number of adsorption sites, and the metal binding constant (van den Berg and Dharmvanij, 1984). In this case this is equivalent to a K'CL value of about 400. ...
Page 1. I шмиш ELSEVIER Marine Chemistry 59 (1998) 283-300 ===== Variability in the speciation of... more Page 1. I шмиш ELSEVIER Marine Chemistry 59 (1998) 283-300 ===== Variability in the speciation of iron in the northern North Sea Martha Gledhill a ', Constant MG van den Berg a*, Rob F. Nolting b, Klaas R. Timmermans ...
ABSTRACT Preliminary measurements of sulfide in seawater using cathodic stripping voltammetry and... more ABSTRACT Preliminary measurements of sulfide in seawater using cathodic stripping voltammetry and a hanging mercury drop electrode (HMDE) in batch-mode showed that the sulfide peak decreased rapidly with time. This decrease was not caused by O2, H2O2 or IO3−, and the sulfide peak was not stabilised by trace metal additions. A home-made flow-cell was constructed to enable the determination of sulfide in seawater using voltammetry with an HMDE. A stable sulfide peak was obtained by flow-analysis with voltammetric detection, with a precision of 2.8% and detection limit of 0.5 nM at a 60 s adsorption time. Several thiol compounds were found to produce a peak at, or very close to, the peak potential for sulfide. Their interference was evaluated by allowing the sulfide peak in conventional (batch) voltammetry to decay. Comparative experiments showed that waste metallic mercury is responsible for removal of sulfide in batch-mode analysis due to formation of insoluble mercuric sulfide salts causing the rapid decay of the sulfide peak. The problem is circumvented by using flow-analysis to determine sulfide.
Apparatus is designed and tested to determine metals in situ in seawater. Voltammetry with a vibr... more Apparatus is designed and tested to determine metals in situ in seawater. Voltammetry with a vibrating gold microwire electrode (VGME) is combined with a battery powered potentiostat and a processor board and is tested for in situ monitoring of copper (Cu) in coastal waters. The VGME was combined with solid state reference and counter electrodes to make a single vibrating probe which was rated up to a depth of 40 m. The measuring mode for Cu was square-wave anodic stripping voltammetry whilst dissolved oxygen (DO) was monitored by a linear sweep scan in a negative potential direction. The working electrode was reactivated between measurements using a suitable potential sequence. The novelties of this work are the field-testing of apparatus incorporating a VGME for copper monitoring, which eliminates the need for pumping and reagents, but has sufficient sensitivity for low ambient levels of copper, and the use of a novel potential sequence to stabilise the response over a long time period. The apparatus has a measuring time of about 6 weeks and a measuring frequency of 12 h(-1). Measurement is reagent-free and power use is low as no pump is required. Experiments are carried out to test the stability of response of the system at various temperatures and its robustness with respect to long-term copper monitoring. Preliminary data were obtained during autonomous deployment over several weeks on a buoy in the Irish Sea. Vertical movement of the buoy caused individual measurements to have a variability of about 15%. It was found that longer term variability of the electrode could be minimised by normalisation of the Cu response over that of DO as the response was related to diffusion through the electrode surface which was similarly affected. The detected fraction of Cu (labile Cu) amounted to 1.5-4 nM during different deployments at a total Cu concentration of ∼10 nM. The same ratio was found by voltammetry in samples taken to the laboratory. The new apparatus has demonstrated that metals in coastal waters can be monitored at trace level, much facilitating the monitoring of outfalls and local water contamination. Because of its sensitivity the apparatus would be of use in estuarine as well as coastal waters, with the aim of monitoring intermittent variability in the copper concentration.
International Journal of Environmental Analytical Chemistry, 1998
Intern. J. Envimn.A~l. Chem..Vol.l1(1),pp. 1-17 Reprints available directly from Ihe publisher Ph... more Intern. J. Envimn.A~l. Chem..Vol.l1(1),pp. 1-17 Reprints available directly from Ihe publisher Photocopying permitted by license only ... 0 1998 OPA (OvaMPs Publishers Association) Amsterdam NV Published by license under the Gordon and Breach Science P ublish imprint. Printed ...
Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry ... more Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry (CSV), is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV. This work presents the CSV method to determine As(III) in high-iron or -manganese groundwaters in the field with only minor sample treatment. The method was field-tested in West-Bengal (India) on a series of groundwater samples. Total arsenic was subsequently determined after acidification to pH 1 by anodic stripping voltammetry (ASV). Comparative measurements by ICP-MS as reference method for total As, and by HPLC for its speciation, were used to corroborate the field data in stored samples. Most of the arsenic (78±0.02%) was found to occur as inorganic As(III) in the freshly collected waters, in accordance with previous studies. The data shows that the modified on-site CSV met...
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