Constant Van Den Berg | University of Liverpool (original) (raw)

Papers by Constant Van Den Berg

Analytical Proceedings, 1988

In situ effects of ocean acidification are increasingly studied at submarine CO2 vents. Here we p... more In situ effects of ocean acidification are increasingly studied at submarine CO2 vents. Here we present a preliminary investigation into the water chemistry and biology of cool temperate CO2 vents near Whakaari–White Island, New Zealand. Water samples were collected inside three vent shafts, within vents at a distance of 2 m from the shaft and at control sites. Vent samples contained both seawater pH on the total scale (pHT) and carbonate saturation states that were severely reduced, creating conditions as predicted for beyond the year 2100. Vent samples showed lower salinities, higher temperatures and greater nutrient concentrations. Sulfide levels were elevated and mercury levels were at concentrations considered toxic at all vent and control sites, but stable organic and inorganic ligands were present, as deduced from Cu speciation data, potentially mediating harmful effects on local organisms. The biological investigations focused on phytoplankton, zooplankton and macroalgae. In...

Eos Transactions American Geophysical Union

Analytica Chimica Acta, 1990

ABSTRACT

ACS Symposium Series, 1979

Page 1. 6 Conditional Stability Constants for Copper Ions with Ligands in Natural Waters CONSTANT... more Page 1. 6 Conditional Stability Constants for Copper Ions with Ligands in Natural Waters CONSTANT MG VAN DEN BERG and JAMES R. KRAMER Department of Geology, McMaster University, Hamilton, Ontario, Canada L8S 4M1 ...

Frontiers in Marine Science, 2017

The concentrations of dissolved copper (Cu d), copper-binding ligands, thiourea-type thiols, and ... more The concentrations of dissolved copper (Cu d), copper-binding ligands, thiourea-type thiols, and humic substances (HS Cu) were measured in estuarine waters adjacent to Sapelo Island, Georgia, USA, on a monthly basis from April to December 2014. Here we present the seasonal cycle of copper speciation within the estuary and compare it to the development of an annually occurring bloom of Ammonia Oxidizing Archaea (AOA), which require copper for many enzymes. Two types of complexing ligands (L 1 and L 2) were found to dominate with mean complex stabilities (log K ′ CuL) of 14.5 and 12.8. Strong complexation resulted in lowering the concentration of free cupric ion (Cu 2+) to femtomolar (fM) levels throughout the study and to sub-fM levels during the summer months. A Thaumarchaeota bloom during this period suggests that this organism manages to grow at very low Cu 2+ concentrations. Correlation of the concentration of the L 1 ligand class with a thiourea-type thiol and the L 2 ligand class with HS Cu provide an interesting dimension to the identity of the ligand classes. Due to the stronger complex stability, 82-99% of the copper was bound to L 1. Thiourea-type thiols typically form Cu(I) species, which would suggest that up to ∼90% copper could be present as Cu(I) in this region. In view of the very low concentration of free copper (pCu > 15 at the onset and during the bloom) and a reputedly high requirement for copper, it is likely that the Thaumarchaeota are able to access thiol-bound copper directly.

Limnology and Oceanography, 1999

Marine microalgae (Emiliania huxleyi) were grown in seawater enriched only with nitrogen and phos... more Marine microalgae (Emiliania huxleyi) were grown in seawater enriched only with nitrogen and phosphorus, without control of free metal concentrations using synthetic chelators. Complexing ligands and thiol compounds were determined by cathodic stripping volt-ammetry. Copper was added to these cultures, and ligands were produced in response to the copper addition. Parallel measurements of thiols showed that glutathione and other unidentified thiols (electrochemically similar to thioacetamide) were produced by the algae at rates and concentrations similar to those of the complexing ligands. Smaller amounts of thiols were produced when ligands including thiols were added to the culture. The results indicate that thiols can account for a major part or most of the copper-complexing ligands produced by these algae. Furthermore, a feedback mechanism exists in which the production of thiol-type complexing ligands is controlled by the free copper concentration, production already being stimulated by an increase of [Cu 2ϩ ] from 0.4 to 1.5 pM. Incubations with added exudates, thiols, and salicylaldoxime (SA) showed much reduced copper toxicity even though copper uptake was increased by the exudates and the SA. Culture experiments have shown that marine and freshwater phytoplankton release complexing ligands into culture medium (e.g., van den Berg et al. 1979; Imber and Robinson 1983), which may be important because the availability of metals to algae is known to depend on their chemical composition (e.g., Brand et al. 1983). Therefore, the interaction of phytoplankton with trace metals is reciprocal: the biota affect the trace metal chemistry and the trace metals affect the biota. Using marine algal cultures where the metal chemistry was controlled by a synthetic chelator (usually ethylenediaminetetraacetic acid [EDTA]), the biological uptake of copper has been shown to be related to the cupric ion concentration, [Cu 2ϩ ] (e.g., Brand et al. 1986); toxicity occurs at pM levels of Cu 2ϩ. The concentration of Cu 2ϩ is typically lowered by by 2-3 orders of magnitude by organic complexation in seawater to a [Cu 2ϩ ] of 0.03-0.3 pM, which is thought to be sufficiently high to meet algal nutritional requirements but is below copper toxicity levels (Sunda 1995).

Environmental Chemistry, 2014

Environmental context Identifying the source and stimuli responsible for organic ligands in seawa... more Environmental context Identifying the source and stimuli responsible for organic ligands in seawater is crucial to understanding trace metal availability. Voltammetric techniques were employed to characterise the water chemistry of seaweed cultures exposed to low levels of Cu or Zn over 7 days. The results suggest that seaweeds are a potential source of metal complexing ligands and Cu and Zn appear to stimulate ligand production; further research is required to determine if this is applicable to macroalgae and metals outside this study. It is widely accepted that organic ligands control metal speciation in seawater, although little is known about their source, stimuli or identity. To gain insight on the possible environmental controls of metal complexing ligands (L), three brown macroalgae common in Irish waters (Ascophyllum nodosum, Fucus vesiculosus and Laminaria hyperborea) were cultured under low levels of Cu (0, 7.86 or 15.7nM) or Zn (0, 15.2 or 91.7nM) exposure. Seaweed chloro...

Electroanalysis, 1994

The voltammetric determination of trace metals in seawater suffers from the interference of disso... more The voltammetric determination of trace metals in seawater suffers from the interference of dissolved oxygen and engine vibrations onboard ship. It is here attempted to overcome these interferences using a high-frequency (1 to 20 Hz) staircase modulation during the voltammetric scan (highperformance adsorptive cathodic stripping voltammetry, HPACSV). Comparative experiments using the square-wave modulation showed that this modulation was not effective at such a high frequenq. A comparison between various complexing agents (DMG and nioxime) and pH buffers (HEPES/NH40H, borate/NaOH, and TEA/NH40H) showed that the determination of nickel and cobalt was similarly improved by the high-speed potential scan in all conditions. Fast potential scans cause a large increase of the peak area and peak heights using staircase modulation. The peaks are wider, and the peak potentials are shifted toward negative values due to the ohmic drop, but the.analytica1 determination is not disturbed. Optimal sensitivity for the determination of cobalt and nickel in seawater was obtained using TEA buffer and DMG as the adsorptive ligand. The nioxime wave was found to interfere in the cobalt peak at high scan rates so that this ligand is not recommended for HPACSV. Comparative tests showed that the sensitivity for nickel and cobalt determinations was highly improved by the fast scan rates. Furthermore, the reduction current of dissolved oxygen was partially masked so that measurements could be taken without a previous purge of the sample. Finally, the scans were insensitive to the solution turbulence so measurements could be readily carried out onboard of an oceanographic vessel or without switching off the stirrer. Low levels of nickel (2 nM) could be determined in seawater by using a deposition time of 20 seconds and of 120 seconds for 0.05 nM cobalt from turbulent and unpurged solutions. A fast determination method for labile nickel and cobalt is proposed.

Electroanalysis, 1998

Existing electrochemical methods for the determination of iron require long deposition times to d... more Existing electrochemical methods for the determination of iron require long deposition times to determine low iron levels. Here a new method, based on catalytic cathodic stripping voltammetry, is described to determine subnanomolar levels of iron in seawater. The new method has a better baseline and is generally simplified, leading to a lower reagent blank and minimized sample handling compared to a previous catalytic method [1]. Optimized conditions include the addition of 20 M 1-nitroso-2-naphthol (NN), 40 mM bromate, and 0.01 M HEPPS pH buffer, giving measurements in pH 8 seawater. The detection limit is 0.08 nM Fe after an adsorption time of 30 s; the detection limit is lowered by increasing the adsorption time. The method can also be used to determine the redox speciation of iron: Fe III is determined specifically by masking Fe II with 2,2bipyridyl (Bp). The concentration of Fe II can then be calculated by difference from the total iron concentration.

Analytical Chemistry, 1987

Page 1. 924 Anal. Chem. 1987, 59, 924-928 AIDS FOR ANALYTICAL CHEMISTS Direct Determination of Ur... more Page 1. 924 Anal. Chem. 1987, 59, 924-928 AIDS FOR ANALYTICAL CHEMISTS Direct Determination of Uranium in Water by Cathodic Stripping Voltammetry Constant M. G. van den Berg* and Malcolm Nimmo Department ...

Analytical Chemistry, 1985

Complex ions of moiybdenum(V1) with 8-hydroxyqulnoilne (oxine) are shown to adsorb onto the hangi... more Complex ions of moiybdenum(V1) with 8-hydroxyqulnoilne (oxine) are shown to adsorb onto the hanging mercury drop electrode. This property forms the basls of a sensitive electrochemical technique by which dissolved molybdenum in seawater can be determined directly. The reduction current of adsorbed complex ions Is measured by differential pulse adsorption voltammetry, preceded by a period of 1 or 2 min of unstlrred collection at an adsorption potential of-0.2 V. I n the presence of 2 X lo-' M oxlne and at pH 2.5 the potential of the main reduction peak is located at-0.59 V. The peak current-molybdenum concentratlon relationship is linear up to 3 X lo-' M; the detection limit is 4 nM. Greater sensitivity is obtained after stlrred collection at pH 3.0 and with lo4 M oxine, but the cailbration curve is nonilnear. I n these conditions the limit of detectlon lies at lo-'' M after 10 min stlrred collection. The concentration of dissolved molybdenum in seawater typically lies in the range of (1.0-1.3) X

Analytica Chimica Acta, 2012

Innovative use of ligand competition to measure dissolved forms of complexed Fe II. Use of light ... more Innovative use of ligand competition to measure dissolved forms of complexed Fe II. Use of light waveguide capillary cell for low concentrations of Fe II. Method estimates concentration and conditional stability constants of Fe II ligands. Provides a new tool to study redox cycling of iron in natural aquatic systems.

Frontiers in Marine Science, 2016

P r o v i s i o n a l This Provisional PDF corresponds to the article as it appeared upon accepta... more P r o v i s i o n a l This Provisional PDF corresponds to the article as it appeared upon acceptance, after peer-review. Fully formatted PDF and full text (HTML) versions will be made available soon.

Analytical Chemistry, 1995

An automated method for on-site monitoring of uranium-(VI) in raftbate streams originating h m nu... more An automated method for on-site monitoring of uranium-(VI) in raftbate streams originating h m nuclear fuel reprocessing plants is described. An in-line stripping procedure (based on liquid/liquid extraction) was developed to extract U(VI) h m this stream, a solvent mixture of 20% tributyl phosphate and nitric acid in kerosene, into an aqueous sodium sulfate solution. Degradation products in the solvent mixture, especially dibutyl phosphate, give rise to very strong complexes and are responsible for moderate but constant U(VI) recoveries (-50%). Optimal conditions for in-line stripping comprise a mixing ratio of extractant (0.5 M sodium sulfate in water)/solvent mixture of-3 and a pumping rate of-0.4 mL min-' of the solvent mixture. The determination of U(VI) was by on-line cathodic stripping voltammmetty (o, preceded by adsorptive collection of the U(VI) as an oxine complex onto a hanging mercury drop electrode. Quantities of 1-2 mL of the aqueous extract were pumped into the voltammetric cell and diluted (1/5 to 1/10) with a background electrolyte containing 0.1 M PIPES buffer, 2 x M oxine, M EDTA, and 0.2 M hydrazine hydrate @H 9.0). The CSV peak for U(VI) was obtained at-0.68 Vwith a detection limit of 20 nM in the raftinate stream using an adsorption lime of 120-s. Both the inline stripping procedure and the on-line measurement were fully automated, with a relative standard deviation in the measurements of <5%. This study describes a method for the determination of hexavalent uranium (U0) in mixtures of tributyl phosphate m P) and kerosene. These solvents are used in the reprocessing of nuclear fuels. In this process, the "unbumt" uranium is separated from plutonium and other radioactive fission products. To this end, the "spent" fuel elements are dissolved in concentrated nitric acid, and the U O in the resulting solution is extracted, puriiled, and preconcentrated with a TBP/kerosene mixture (usually-20% TBP in kerosene) in a three-step procedure:' In the first step, u r a n i u m 0 and plutonium0 are separated together from the fission products; u r a n i u m 0 and plutonium0 are extracted into the organic phase, and the fission

Electroanalysis, 1999

Cathodic stripping voltammetry (CSV) is subject to interference by engine vibrations when used on... more Cathodic stripping voltammetry (CSV) is subject to interference by engine vibrations when used on-board ship. Scanning wave-forms utilizing high-frequency potential modulations can to some extent overcome this problem, but these cannot be used for catalytic CSV without major loss of sensitivity. To minimize the effects of vibrations an antivibration electrode support was developed based on a PVC plate suspended from elastic bands. The support was compared to the more simple expedient of placing the electrode on large rubber (``Hi-Fi'') feet. Successful damping was evaluated from ship-board determinations of iron in seawater by catalytic CSV. The rubber feet were found to lower the relative standard deviation (RSD) of these measurements to 34 % from 70 % without damping. The antivibration support was found to lower the RSD to an acceptable 10 % and was used extensively for voltammetry on-board ship.

Amino Acids, 2014

ABSTRACT A linear sweep voltammetric method is used for direct simultaneous determination of L-cy... more ABSTRACT A linear sweep voltammetric method is used for direct simultaneous determination of L-cysteine and L-cysteine disulfide (cystine) based on carbon ionic liquid electrode. With carbon ionic liquid electrode as a high performance electrode, two oxidation peaks for L-cysteine (0.62 V) and L-cysteine disulfide (1.3 V) were observed with a significant separation of about 680 mV (vs. Ag/AgCl) in phosphate buffer solution (pH 6.0). The linear ranges were obtained as 1.0-450 and 5.0-700 μM and detection limits were estimated to be 0.298 and 4.258 μM for L-cysteine and L-cysteine disulfide, respectively. This composite electrode was applied for simultaneous determination of L-cysteine and L-cysteine disulfide in two real samples, artificial urine and nutrient broth. Satisfactory results were obtained which clearly indicate the applicability of the proposed electrode for simultaneous determination of these compounds in complex matrices.

Marine Pollution Bulletin, 2008

Continental inputs of copper via rivers and sewage into the Vigo Ria were evaluated. The main flu... more Continental inputs of copper via rivers and sewage into the Vigo Ria were evaluated. The main fluvial input is not contaminated and the most degraded discharges occur on the southern margin of the middle ria. Continental inputs of copper and ligands to the ria are dominated by sewage treatment plants (136 mol Cu day(-1), 124 mol L day(-1)) supported by rivers (15 mol Cu day(-1), 21 mol L day(-1)). The dissolved fraction is the main channel of discharge for rivers (66%) with particulate matter being predominant in sewage (63%). Dissolved copper is organically complexed both in rivers (99.8%) and sewage (99.9%). This minor difference may be attributed to the fact that the stability of sewage complexes is greater than those in rivers. Moreover, ligand concentrations are higher in sewage than in rivers. Thus, the natural continental inputs of copper and ligands into the ria are magnified by anthropogenic inputs (5-15 and 3-5 times higher for copper and ligands, respectively).