Determination of iodide and total iodine in estuarine waters by cathodic stripping voltammetry using a vibrating silver amalgam microwire electrode.

Iodide in natural waters is an important nutrient to aquatic organisms and its determination is of relevance to marine aquaculture. For this reason it is of interest to have a simple analytical method for determination of iodide in water samples. Iodide in seawater can be determined electrochemically by cathodic stripping voltammetry (CSV) with a mercury drop electrode which has environmental drawbacks.

Determination of chromium in estuarine waters by catalytic cathodic stripping voltammetry using a vibrating silver amalgam microwire electrode.

Chromium (Cr(VI)) in water can be determined by adsorptive catalytic cathodic stripping voltammetry in the presence of diethylenetriaminepentaacetic acid (DTPA) and nitrate on the hanging mercury drop electrode (HMDE). Predominately Cr(VI) is detected and the water is UV-digested to convert all Cr to Cr(VI) prior to analysis. We develop here an alternative to the HMDE by using a silver amalgam electrode based on a vibrating microwire.

Determination of lead and cadmium in seawater using a vibrating silver amalgam microwire electrode.

Silver amalgamated electrodes are a good substrate to determine lead (Pb) and cadmium (Cd) in seawater because they have properties similar to mercury but without the free mercury (Hg). Here a silver amalgamated microwire (SAM) electrode is optimised for the determination of Pb and Cd in coastal waters and uncontaminated ocean waters. The SAM was vibrated during the deposition step to increase the sensitivity, and electroanalytical parameters were optimised.

Sulfide determination in hydrothermal seawater samples using a vibrating gold micro-wire electrode in conjunction with stripping chronopotentiometry.

A rapid electrochemical stripping chronopotentiometric procedure to determined sulfide in unaltered hydrothermal seawater samples is presented. Sulfide is deposited at -0.25 V (vs Ag/AgCl, KCl 3M) at a vibrating gold microwire and then stripped through the application of a reductive constant current (typically -2 μA).

Apparatus for in situ monitoring of copper in coastal waters.

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.

Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode.

The oxidation potentials of As(0)/As(III) and Sb(0)/Sb(III) on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10-20 nM), Sb occurring at ~0.1 time that of As.

Pseudopolarography of copper complexes in seawater using a vibrating gold microwire electrode.

Copper (Cu) in seawater can be determined by anodic stripping voltammetry using a vibrating gold microwire electrode (VGME) with a much lower limit of detection than using a mercury electrode, enabling detection of labile Cu at trace level. The possibility of pseudopolarography of Cu using the VGME is investigated here and is calibrated against known chelating agents. The sensitivity much (15-fold) improved by application of a desorption step to remove adsorbed organic substances and excess anions.

Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode.

Direct electrochemical determination of arsenate (As(V)) in neutral pH waters is considered impossible due to electro-inactivity of As(V). As(III) on the other hand is readily plated as As(0) on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As(V) to As(III) was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn(II).

Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode.

In this work, a simple, rapid, reliable and low cost method for simultaneous electrochemical determination of As, Cu, Hg and Pb ions, on a vibrating gold microwire electrode combined with stripping voltammetry, is described for the first time. The multi-element detection was performed in the presence of oxygen by differential pulse anodic stripping voltammetry (DPASV) in HCl 0.1 M with NaCl 0.

Voltammetric determination of arsenic in high iron and manganese groundwaters.

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.

Beyond the hydrogen wave: new frontier in the detection of trace elements by stripping voltammetry.

Stripping voltammetry is limited in acidic conditions to relatively high deposition potentials because of the interfering effects of the hydrogen produced at the working electrode. We report here a simple procedure to perform reliable and sensitive trace metal analysis in such conditions. Measurements are made at a gold microwire electrode.

Arsenic speciation in natural waters by cathodic stripping voltammetry.

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.

Metal complexation by humic substances in seawater.

We determined the complex stability of copper, zinc, cobalt and aluminum with humic acid (HA) and fulvic acid (FA) in pH 8 seawater. The method is based on metal competition against iron, for which the complex stability with humic substances (HS) in seawater had been calibrated previously against EDTA. The conditional stability constants, log K'(Mn+HS) values, were found to decrease in the order of Cu > Zn > Co and Fe > Al.

Benthic fluxes of copper, complexing ligands and thiol compounds in shallow lagoon waters.

Benthic fluxes of copper, copper complexing ligands and thiol compounds in the shallow waters of Venice Lagoon (Italy) were determined using benthic chambers and compared to porewater concentrations to confirm their origin. Benthic copper fluxes were small due to small concentration differences between the porewaters and the overlying water, and the equilibrium concentration was the same at both sites, suggesting that the sediments acted to buffer the copper concentration. Thiol fluxes were approximately 10 x greater at 50-60 pmol cm(-2)h(-1), at the two sites.

Determination of humic substances in natural waters by cathodic stripping voltammetry of their complexes with iron.

A new voltammetric method is presented for the measurement of humic substances (HS) in natural waters. The method is based on catalytic cathodic stripping voltammetry (CSV) and makes use of adsorptive properties of iron-HS complexes on the mercury drop electrode at natural pH. A fulvic acid standard (IHSS) was used to confirm the voltammetric response (peak potential and sensitivity) for the HS for natural water samples.

Advantages of using a mercury coated, micro-wire, electrode in adsorptive cathodic stripping voltammetry.

A mercury coated, gold, micro-wire electrode is used here for the determination of iron in seawater by catalytic cathodic stripping voltammetry (CSV) with a limit of detection of 0.1 nM Fe at a 60s adsorption time. It was found that the electrode surface is stable for extended periods of analyses (at least five days) and that it is reactivated by briefly (2s) applying a negative potential prior to each scan.

Wavelength dependence of the photochemical reduction of iron in arctic seawater.

Chemiluminescence measurements of the photochemical reduction of iron in cold, high-latitude waters (79 degrees N) show that a significant fraction (20%) of the dissolved iron is reduced when exposed to sunlight. The reduction is immediately initiated and the transition to a steady-state concentration of approximately 200 pM photochemical Fe(II) is achieved within approximately 40 s. The photochemical Fe(ll) is reoxidized to Fe(III) in less than a minute upon blocking the sunlight, much faster than expected, which is ascribed to reaction with photochemically produced oxidants.

Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode.

The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously.

Voltammetric detection of mercury and copper in seawater using a gold microwire electrode.

A procedure is presented by which mercury and copper are determined simultaneously in seawater and dilute acid (0.01 M HCl) by anodic stripping voltammetry using gold microwire electrodes. It was found that anion (halide) adsorption is the cause for a gradual decrease in the height and potential of the mercury peak.

Chemical speciation of iron in seawater by cathodic stripping voltammetry with dihydroxynaphthalene.

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 microM, seawater at its original pH of 8, and equilibration overnight.

Microbenthic chamber with microelectrode for in-situ determination of fluxes of dissolved S(-II), I-, O2, Mn, and Fe.

A 2-mL microbenthic chamber was fitted with a microelectrode for the in-situ determination of benthic fluxes of S(-II), I-, O2, Mn(II), and Fe(I). Detection was by voltammetry using a battery operated potentiostat and a gold microelectrode. The chamber was fitted on a Perspex plate to be placed on sediments.

Determination of metal speciation by reverse titrations.

A new method is proposed to determine metal speciation by varying the concentration of a competing ligand at a constant metal concentration, with detection by cathodic stripping voltammetry. The free metal ion concentration is gradually lowered from its natural level while the method probes progressively deeper into the already complexed metal fraction: it is therefore a reverse titration rather than the forward titration which is used for conventional complexing ligand titrations. The sensitivity is greatest at the lowest free metal ion concentration, where it matters most, and the method can be carried out in a single sample aliquot in the voltammetric cell.