Pascal Salaün

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 0.5 M. This media was found optimum in terms of peak resolution, peak shape and sensitivities, and has a composition similar to seawater to which the method could potentially be applied. The gold microwire electrode presented well defined, undistorted, sharp and reproducible peaks for trace concentrations of Cu, Hg and Pb and As presented a reproducible peak with a small shoulder. Using a gold vibrating microwire electrode of 25 μm diameter and 30s deposition time, the detection limits of As, Cu, Hg and Pb were 0.07, 0.4, 0.07 and 0.2 μgL(-1), respectively. Possible effects of Al, Cd, Cr, Fe, Mn, Ni, Sb and Zn were investigated but did not cause any significant interferences. Finally, the method was applied for the simultaneous determination of these four metals in unpolluted river water samples and the results were validated by Atomic Absorption Spectroscopy with Electrothermal Atomization (AAS-EA) or by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

Critical review perspective: elemental speciation analysis methods in environmental chemistry – moving towards methodological integration

Environmental context. Elemental speciation defines mobility, accumulation behaviour and toxicity of elements in the environment. Environmental processes are then modelled using species information. Hence, it is important for environmental chemists to rely on unequivocal, precise and accurate analytical data for the identification and quantification of elemental species. Abstract. We review the application of speciation analysis used in environmental chemistry studies to gain information about the molecular diversity of elements in various environmental compartments. The review focuses on three major analytical methodologies: electrochemical, X-ray absorption spectroscopy, and methods that couple chromatography with mass spectrometric detection. In particular, the review aims to highlight the advantages and disadvantages of the three methods, and to demonstrate that both the chemistry of the element and the nature of the environmental compartment determine the choice of the preferred analytical technique. We demonstrate that these two factors can lead to technique-dependent shortcomings that contribute to the current gaps in knowledge of elemental speciation in the environment. In order to fill those gaps, multi-method approaches are urgently needed. Finally, we present a selection of recent studies that exhibit the potential to use complementary techniques to overcome method-dependent limitations in order to reduce ambiguities and to gain more confidence in the assignment of the molecular structure of elements in environmental samples.

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. 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 microM 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.

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.

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.

COST action TD1407: network on technology-critical elements (NOTICE)—from environmental processes to human health threats

The current socio-economic, environmental and public health challenges that countries are facing clearly need common-defined strategies to inform and support our transition to a sustainable economy. Here, the technology-critical elements (which includes Ga, Ge, In, Te, Nb, Ta, Tl, the Platinum Group Elements and most of the rare-earth elements) are of great relevance in the development of emerging key technologies—including renewable energy, energy efficiency, electronics or the aerospace industry. In this context, the increasing use of technology-critical elements (TCEs) and associated environmental impacts (from mining to end-of-life waste products) is not restricted to a national level but covers most likely a global scale. Accordingly, the European COST Action TD1407: Network on Technology-Critical Elements (NOTICE)—from environmental processes to human health threats, has an overall objective for creating a network of scientists and practitioners interested in TCEs, from the evaluation of their environmental processes to understanding potential human health threats, with the aim of defining the current state of knowledge and gaps, proposing priority research lines/activities and acting as a platform for new collaborations and joint research projects. The Action is focused on three major scientific areas: (i) analytical chemistry, (ii) environmental biogeochemistry and (iii) human exposure and (eco)-toxicology.

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. After applying a simple electrochemical conditioning procedure, hydrogen does not block the electrode, allowing reproducible analysis and smooth stripping signals to be obtained. Advantages of working inside the hydrogen wave are exemplified through the detection of the often considered electroinactive antimony(V). Sb(V) is detected in relatively low acidic conditions (pH ≤ 1) using low deposition potentials (≤-1.8 V). The detection limit is 5 pM (0.63 ppt), the lowest ever reported for an electroanalytical technique and one of the lowest analytical methods. The method is simple, robust, and free from the common arsenic interference due to selective electrochemical hydride generation of arsine over stibine during the deposition step. Analytical methods were optimized and tested on mineral, river, tap, and coastal seawater. Results favorably compare against Certified Reference Materials data (NASS-4 and SLRS-3) and ICPMS analysis. Deposition well below the hydrogen wave pushes the frontier of stripping voltammetry, and new analytical applications in this combined range of acidity and deposition potential are to be expected.

Hepatotoxicity of Pentavalent Antimonial Drug: Possible Role of Residual Sb(III) and Protective Effect of Ascorbic Acid

ABSTRACT Pentavalent antimonial drugs such as meglumine antimoniate (Glucantime [Glu; Sanofi-Aventis, São Paulo, Brazil]) produce severe side effects, including cardiotoxicity and hepatotoxicity, during the treatment of leishmaniasis. We evaluated the role of residual Sb(III) in the hepatotoxicity of meglumine antimoniate, as well as the protective effect of the antioxidant ascorbic acid (AA) during antimonial chemotherapy in a murine model of visceral leishmaniasis. BALB/c mice infected with Leishmania infantum were treated intraperitoneally at 80 mg of Sb/kg/day with commercial meglumine antimoniate (Glu) or a synthetic meglumine antimoniate with lower Sb(III) level (MA), in association or not with AA (15 mg/kg/day), for a 20-day period. Control groups received saline or saline plus AA. Livers were evaluated for hepatocytes histological alterations, peroxidase activity, and apoptosis. Increased proportions of swollen and apoptotic hepatocytes were observed in animals treated with Glu compared to animals treated with saline or MA. The peroxidase activity was also enhanced in the liver of animals that received Glu. Cotreatment with AA reduced the extent of histological changes, the apoptotic index, and the peroxidase activity to levels corresponding to the control group. Moreover, the association with AA did not affect the hepatic uptake of Sb and the ability of Glu to reduce the liver and spleen parasite loads in infected mice. In conclusion, our data supports the use of pentavalent antimonials with low residue of Sb(III) and the association of pentavalent antimonials with AA, as effective strategies to reduce side effects in antimonial therapy.

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. The notorious tendency of solid electrodes to be affected by memory effects was overcome by a conditioning interval between measurements that stabilized the electrode response. Model ligands, including EDTA, humic substances (HS), and glutathione (examples of natural ligands) were analyzed to calibrate the half-wave shift to complex stability. The half-wave shift on the VGME is much greater (~2×) than that on the mercury drop electrode which is attributed to several parameters including a much (5-fold) thinner diffusion layer on the VGME. Experiments showed that the same procedure is suitable for pseudopolarography of zinc. Application of the new method to samples from the Irish Sea showed Cu occurring in several complexes, all strongly bound, and some occurring in the electrochemically reversible region of the pseudopolarogram. The humic substance complex of Cu was also found to occur in the reversible region of the pseudopolarogram. The pseudopolarograms of Cu in seawater were unaffected by sample filtration and did not require purging to remove dissolved oxygen, suggesting that this method can be readily used as part of an in situ measuring system.

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. 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 method for As(III) is a good measure of water contamination with As. The EDTA was also found to be effective in stabilising the arsenic speciation for longterm sample storage at room temperature. Without sample preservation, in water exposed to air and sunlight, the As(III) was found to become oxidised to As(V), and Fe(II) oxidised to Fe(III), removing the As(V) by adsorption on precipitating Fe(III)-hydroxides within a few hours.