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. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH ≤2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5 μm diameter wire is 0.7 μm. The detection limits for the As(III) and Sb(III) are below 0.1 nM using 2 min and 10 min deposition times respectively. As(III) and Sb(III) can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As(0) to As(III) was found to proceed through a transient As(III) species. Adsorption of this species on the gold electrode at potentials where Sb(III) diffused away is used for selective deposition of As(III). Addition of EDTA removes the interfering effect of manganese when analysing As(III). Imposition of a desorption step for Sb(III) analysis is required. Total inorganic arsenic (iAs=As(V)+As(III)) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6<pH<2 using E(dep)=-1 V. Total inorganic antimony (iSb=Sb(V)+Sb(III)) is determined at pH 1 using E(dep)=-1.8 V without interference by As. The methods were tested in samples from the Irish Sea (Liverpool Bay). As(III) was determined on-board ship immediately after sampling. As(III) concentrations were found to range from 0.44 to 1.56 nM and were higher near the coast. Sb(III) was below the detection limit (<0.1 nM Sb(III)), iAs was comprised between 8 and 25 nM while iSb varied from 0.5 to 1.7 nM.

Salaün P ，Gibbon-Walsh KB ，Alves GM ，Soares HM ，van den Berg CM ... -  《-》

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

Salaün P ，Planer-Friedrich B ，van den Berg CM 《-》

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). Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As(V) in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (~1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of -1.3 V. Deposition of As(0) from dissolved As(V) caused elemental Mn to be re-oxidised to Mn(II) in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As(V) is subsequently quantified using an ASV scan. As(III) interferes and should be quantified separately at a more positive deposition potential of -0.9 V. Combined inorganic As is quantified after oxidation of As(III) to As(V) using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As(V) using a deposition time of 180 s.

Gibbon-Walsh K ，Salaün P ，van den Berg CM 《-》

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

Salaün P ，Gibbon-Walsh K ，van den Berg CM 《-》

Unexpectedly high levels of antimony (III) in the pentavalent antimonial drug Glucantime: insights from a new voltammetric approach.

Salaün P ，Frézard F 《-》