Square-wave voltammetric stripping analysis of thallium(III) at a poly(4-vinylpyridine)/mercury film electrode

A poly(4-vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square-wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion-exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface-active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illustrated.     

Square-wave anodic stripping voltammetric determination of thallium(I) at a Nafion/mercury film modified electrode

A Nafion/mercury film electrode (NMFE) was used for the determination of trace thallium(I) in aqueous solutions. Thallium(I) was preconcentrated onto the NMFE from the sample solution containing 0.01 M ethylenediaminetetraacetate (EDTA), and determined by square-wave anodic stripping voltammetry (SWASV). Various factors influencing the determination of thallium(I) were thoroughly investigated. This modified electrode exhibits good resistance to interferences from surface-active compounds. The presence of EDTA effectively eliminated the interferences from metal ions, such as lead(II) and cadmium(II), which are generally considered as the major interferents in the determination of thallium at a mercury electrode. With 2-min preconcentration, linear calibration graphs were obtained over the range 0.05-100 ppb of thallium(I). An even lower detection limit, 0.01 ppb, were achieved with 5-min accumulation. The electrode is easy to prepare and can be readily renewed after each stripping experiment. Applicability of this procedure to various water samples is illustrated.     

Mixed polyelectrolyte coatings on glassy carbon electrodes: Ion-exchange, permselectivity properties and analytical application of poly-l-lysine-poly(sodium 4-styrenesulfonate)-coated mercury film electrodes for the detection of trace metals

The present work describes the preparation, optimization and characterization of mixed polyelectrolyte coatings of poly-l-lysine (PLL) and poly(sodium 4-styrenesulfonate) (PSS) for the modification of thin mercury film electrodes (MFEs). The novel-modified electrodes were applied in the direct analysis of trace metals in estuarine waters by square-wave anodic stripping voltammetry (SWASV). The effects of the coating morphology and thickness and also of the monomeric molar ratio PLL/PSS on the cation-exchange ability of the PLL–PSS polyelectrolyte coatings onto glassy carbon (GC) were evaluated using target cationic species such as dopamine (DA) or lead cation. Further, the semi-permeability of the PLL–PSS-coated electrodes based both on electrostatic interactions and on molecular size leads to an improved anti-fouling ability against several tensioactive species. The analytical usefulness of the PLL–PSS-mixed polyelectrolyte coatings on thin mercury film electrodes is demonstrated via SWASV measurements of trace metals (lead, copper and cadmium at the low nanomolar level; accumulation time of 180 s) in estuarine waters containing moderate levels of dissolved organic matter, resulting in a fast and direct methodology requiring no sample pretreatment.     

Effect of surface-active compounds on voltammetric stripping analysis at the mercury film electrode

The effects of various organic compounds on the differential-pulse anodic-stripping voltammetric response at the in-situ plated mercury film electrode are explored. These effects vary from metal to metal and from one organic compound to another. The most pronounced effects are observed in measurements of copper. The main effect of the organic compound is to depress the peak current rather than change the peak shape or potential. The differences between the organic interferences observed at the mercury film electrode and those reported at the hanging mercury drop electrode are explained by the different morphology and geometry of the two electrodes. The implications of these interferences for the reliability and feasibility of stripping measurements in natural waters are discussed. Gelatin, camphor, humic acid, starch, agar, sodium dodecyl sulphate and albumin were used as representative organic compounds, and cadmium, lead, and copper as test metal ions.     

Luminescent bacteria-based sensing method for methylmercury specific determination

A bacterial biosensor method for the selective determination of a bioavailable organomercurial compound, methylmercury, is presented. A recombinant luminescent whole-cell bacterial strain responding to total mercury content in samples was used. The bacterial cells were freeze-dried and used as robust, reagent-like compounds, without batch-to-batch variations. In this bacteria-based sensing method, luciferase is used as a reporter, which requires no substrate additions, therefore allowing homogenous, real-time monitoring of the reporter gene expression. A noninducible, constitutively light-producing control bacterial strain was included in parallel for determining the overall cytotoxicity of the samples. The specificity of the total mercury sensor Escherichia coli MC1061 (pmerRBlux) bacterial resistance system toward methylmercury is due to a coexpressed specific enzyme, organomercurial lyase. This enzyme mediates the cleavage of the carbon–mercury bond of methylmercury to yield mercury ions, which induce the reporter genes and produce a self-luminescent cell. The selective analysis of methylmercury with the total mercury strain is achieved by specifically chelating the inorganic mercury species from the sample using an optimized concentration of EDTA as a chelating agent. After the treatment with the chelating agent, a cross-reactivity of 0.2% with ionic mercury was observed at nonphysiological ionic mercury concentrations (100 nM). The assay was optimized to be performed in 3 h but results can already be read after 1 h incubation. Total mercury strain E. coli MC1061 (pmerRBlux) has been shown to be highly sensitive and capable of determining methylmercury at a subnanomolar level in optimized assay conditions with a very high dynamic range of two decades. The limit of detection of 75 ng/l (300 pM) allows measurement of methylmercury even from natural samples.     

Novel Screen-Printed Gold Nano Film Electrode for Trace Mercury(II) Determination Using Anodic Stripping Voltammetry

Integrating the screen printing technique with the vacuum evaporation method, we developed a novel and disposable screen-printed gold film electrode (SPGFE) in the present work. First, a conductive silver layer, a connection graphite-carbon layer, and an insulating polymer layer were successively printed onto a flexible polyethylene terephthalate (PET) substrate. Then, a gold thin film was achieved on the scheduled vacant site by use of the vacuum evaporation method. In order to enhance the electroanalytical performance of the SPGFE, the thickness of the gold film was controlled in the range of 70–80 nm under optimum conditions. The fabricated SPGFE was applied to detect trace mercury(II) based on the square-wave anodic stripping voltammetry (SWASV). The results indicated that the proposed SPGFE exhibited higher sensitivity to trace mercury(II) than the gold disc electrode. The stripping current was linearly related to the concentration of mercury(II) in the range of 16–280 µg/L (R² = 0.9919) and 1.2–8.0 µg/L (R² = 0.9977), with a detection limit of 0.8 µg/L (S/N = 3) under 180 s accumulation. The SPGFE was further used to detect mercury in real samples, and the obtained results revealed a good agreement with those of inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectroscopy (AAS). The highly sensitive and environmental friendly electrode, as another type of “mercury-free” electrode, holds great promise in stripping measurements.     

Determination of metal ions extracted by DTPA in a soil treated with effluent using an Hg-electroplated-Pt microelectrode

Determinations of Cu, Fe, Mn and Zn were performed in an oxisol soil treated with effluent originated from a biodigester septic cesspool. The extracts were obtained from a DTPA/TEA (pH 7.3) solution and analysed by electroanalytical methodologies using square wave anodic stripping voltammetry (SWASV) for the analysis of Cu, Mn and Zn and square wave voltammetry (SWV) for Fe analysis, both of them with a thin mercury film microelectrode (ME-Hg). DTPA (diethylenetriaminepentaacetic acid) complexes with Cu, Mn and Fe show electroactivity in the potentials range close to the ones for the free ions in solution, but the Zn complex did not show any electroactivity at the potential range analysed. SWASV/ME-Hg and SWV/ME-Hg results were in good agreement (r² = 0.996) with the flame atomic absorption spectroscopy (FAAS) analyses, demonstrating that electroanalytical methodologies can be used for micronutrient determinations in soil extracts without serious interferences of the matrix components. Some characteristics of the complex formed between DTPA-metals are explored by EPR experiments.     

The determination of copper at thin film electrodes by constant current stripping potentiometry

A comparison of the determination of copper by constant current stripping potentiometry (CCSP) at mercury and gold films has been carried out. The preferred solution conditions for the mercury film study were determined to be 0.1M ammonium acetate at pH 4.5 and 0.1M HCl for the gold film study. The influence of chloride on the stripping signal was investigated and it was found that for the mercury film conditions, well-formed stripping signals could be obtained up to a chloride concentration of 0.5 M which permitted the ready determination of copper in seawater. With the gold film, high chloride concentrations affected both the film stability and the glassy carbon surface and repeatable results were difficult to obtain. The optimized CCSP methods were applied to various aqueous samples including tap water, seawater, TCLP (acetic acid) extracts as well as TCLP extracts using groundwater and ocean water. Based on the results obtained for these various matrices, it was concluded that there are several advantages favoring the mercury film. The interference from organic components in the sample matrix on the general applicability of CCSP for the determination of copper at either a mercury or gold film is discussed.     

Optimization of square wave anodic stripping voltammetry (SWASV) for the simultaneous determination of Cd,Pb, and Cu in seawater and comparison with differential pulse anodic stripping voltammetry (DPASV)

Square wave anodic stripping voltammetry (SWASV) was optimized for the simultaneous determination of Cd, Pb and Cu in coastal seawater samples. Background subtraction was adapted to improve peak detection and quantification. Optimum background voltammograms were obtained by applying a 7.5 s equilibration potential at -975 mV (vs. Ag/AgCl, 3M KCl) before starting the background scan. Voltammetric scan parameters were optimized to obtain maximum sensitivity while retaining good peak resolution and discrimination from background. Optimal parameters were: frequency 100 Hz, pulse amplitude 25 mV, current sampling delay time 2 ms, step height 8 mV. The sensitivity of optimized SWASV proved to be more than double that of differential pulse anodic stripping voltammetry (DPASV), and analysis time was halved. Samples containing around 13 (Cd), 30 (Pb), 200 (Cu) ng/l (typical averages of the coastal area of the Marche region) can be analyzed using a 5 min deposition time and the total analysis time using three standard additions is about 1 h and half, excluding the mercury film preparation and the outgassing of the sample, which can be made in parallel using a second cell cup.     

Renewable silver amalgam film electrodes in electrochemical stripping analysis—a review

The success of a voltammetric sensing procedure depends mainly on the proper choice of the working electrode. This is because its ability to accumulate the analyte determines the sensitivity of the method. The main criterion of the selection of the proper working electrode is the available potential window. A variety of conductive materials have been used for the preparation of working electrodes. Of these, two kinds of mercury electrodes—hanging mercury drop and film—were used because of their excellent voltammetric performance and, in particular, their high overpotential of hydrogen reduction. The significant drawbacks of mercury electrodes, however, are the toxicity of the material and the instability of liquid mercury films. To overcome these disadvantages, less toxic mercury-containing materials have been used, such as amalgams and amalgam film electrodes. This group includes renewable silver amalgam film electrodes used for electrochemical stripping sensing purposes. These electrodes have successfully been applied for anodic, adsorptive, cathodic, catalytic voltammetric, and potentiometric stripping determination of trace amounts of inorganic cations and organic compounds in various natural matrices. In this review, the electrode design, characteristics, and application of two kinds of renewable silver amalgam film electrodes are discussed in detail.     

Simultaneous determination of oxygen and mercury in inorganic and organic mercury compounds

Oxygen and mercury in inorganic and organic mercury compounds are determined simultaneously by a modification of the Schütze-Unterzaucher method. The determination of mercury is not influenced by the presence of sulphur and nitrogen in the samples. In 13 inorganic and organic mercury compounds, oxygen has been determined with an error of less than 0.4% and mercury with an error of less than 0.5%.     

Determination of mercury in industrial materials by atomic absorption spectrometry after thermal volatilisation

The pyrolysis of samples containing copper, lead, iron, sulphur compounds and organic carbon is applied to separate mercury prior to its determination by a.a.s. Amalgamation on gold collectors followed by thermal desorption, or trapping in an absorption solution followed by reduction/aeration were used depending on the mercury content in the materials. Appropriate additives to the samples and filters are used to ensure complete release of mercury and removal of interfering pyrolysis products.     

Determination of alkylmercury compounds in fish tissue with an atomic absorption spectrometer used as a specific gas chromatographic detector

Atomic absorption spectrometry is used as a specific gas chromatography detector in the determination of alkylmercury compounds in fish. An electrical furnace “cracks” the organic mercury molecules in the Chromatographic effluent. An extraction procedure has been developed which improves the precision of the method. The detection limit is 0.3 ppm of mercury for 0.5-g samples.     

Fast ultrasound-assisted treatment of urine samples for chronopotentiometric stripping determination of mercury at gold film electrodes

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HC1 and H₂O₂ for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators.     

Perfluorinated anion-exchange polymer mercury film electrode for anodic stripping voltammetric determination of zinc(II): effect of model organic compounds

The determination of zinc ion (1-60 ng ml⁻¹) by anodic square-wave stripping voltammetry on an anion-exchange perfluorinated polymer Tosflex mercury film electrodes (TMFE) was evaluated. The detection limit was 0.1 ng ml⁻¹ Zn(II). The effect of various organic compounds (gelatin, albumin, starch, camphor, humic acid, Triton X-100, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)) is explored. The results indicate that due to the size-exclusion and ion-exchange properties of Tosflex film, the TMFE is considerably more resistant to organic interference than the bare mercury film electrode.     

Determination of copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

The determination of zinc,cadmium, lead and copper in a single sea-water sample by differential pulse anodic stripping voltammetry

A comparative study is described of the anodic stripping voltammetry of sea water at its natural pH and at acetate-buffered pH, with a mercury film electrode. The reproducibility of the oxidation current peaks for copper and lead is improved and the electrode memory effect decreases, when the sample is acetate-buffered (pH 5.8). Determinations of zinc at the natural pH of sea water are inaccurate, because of the formation of Zn—Cu and Zn—Ni intermetallic compounds in the mercury film. The formation of such compounds can be prevented by the addition of gallium ions to acetate-buffered samples. A procedure for the determination of Cu, Pb, Cd and Zn in sea water is described.     

The analysis of organic mercury compounds using liquid chromatography with on-line atomic fluorescence spectrometric detection

A new method for the analysis of organic mercury compounds is reported. The organomercurials are separated by high-performance liquid chromatography (HPLC). The compounds are converted to mercury(0) in a continuous-flow system by means of an oxidizing and a subsequent reducing solution. The elemental mercury generated is swept into the cell of an atomic fluorescence spectrometer (AFS) by a stream of argon. The compositions of the oxidizing solution, which contains peroxodisulphate and copper(II) in dilute sulphuric acid, and the reducing solution, which contains alkaline tin(II) chloride, were optimized, as were the gas–liquid separator (GLS), the condensing system and the geometry of the reaction coils. The method is applied to extracts of certified reference material (CRM) and to river sediments. High concentrations of methylmercury were found in the sediment samples. At one location, the presence of ethylmercury is derived from the sample chromatogram.     

Application of adsorptive stripping voltammetry to the speciation and determination of iron(III) and total iron in wines

An analytical procedure for the determination of iron(III) and total iron in wines based on adsorptive stripping voltammetry is described. Iron(III) was determined by using Solochrome Violet Red as chelating agent while catechol was used for the determination of the total iron content. Each chelate was adsorbed on the hanging mercury electrode and the reduction current of the accumulated chelate was measured. The results obtained from the application of this procedure to wine samples are discussed.     

Application of chromatographic and electrophoretic methodology to the speciation of organomercury compounds in food analysis

Trace metals such as mercury, especially its organic compounds, are an important risk to the environment and to man due to their accumulation in the food chain. For this reason, the routine determination of the very toxic methylmercury, and of other organic and inorganic mercury compounds in marine and land animals, vegetables, fruits and fresh water is of increasing importance in health and environmental control programmes throughout the world. The majority of speciation methods for organomercurials involve a series of fundamental steps for the identification and quantification of samples of biological origin: extraction or isolation from the matrix; derivatisation and concentration; detection; separation of different species of interest and of interference. Each of these steps, as part of the chromatographic analysis of MeHg and of other organomercurials is revised in this study using food samples.