Paolo Ugo

Determination of Trace Mercury in Saltwaters at Screen-Printed Electrodes Modified with Sumichelate Q10R

The results of a study on the determination of trace levels of mercury in natural saltwaters using screen-printed carbon electrodes modified with Sumichelate Q10R, a chelating resin containing dithiocarbamate groups, which binds mercury strongly and selectively are reported. Cyclic voltammetric measurements indicate that mercury(II) is preconcentrated by complexation at the modified electrode, giving peak currents which are about one order of magnitude higher than those obtained at an unmodifed screen-printed electrode. The voltammetric pattern is characterized by a broad reduction peak to which a sharp and well-resolved reoxidation peak is associated. Trace (subnanomolar) concentrations of mercury can be determined at the screen-printed modified electrode by adopting a complexation-anodic stripping procedure with detection via differential pulse voltammetry. The method is characterized by a low detection limit (3j blank/sensitivity) of 12 pM with 20 min complexation and 5 min reduction at ‐0.5 V. Excess copper interferes in the analysis of mercury only when present in more than hundred-fold excess. Data concerning the application of modified screen-printed electrodes to the analysis of mercury in water samples from the channels of Venice (Italy) are presented and discussed.

Ionomer-coated electrodes and nanoelectrode ensembles as electrochemical environmental sensors: Recent advances and prospects

This Minireview focuses on recent advances in the use of ionomer-coated electrodes and nanoelectrode ensembles for the determination of redox ions at trace concentration level with special stress on applications for environmental monitoring. After an overview on the most recent developments of ionomer-coated electrodes, attention is directed towards their use for speciation analysis in environmental samples. In particular, some examples such as the selective determination of inorganic and metallorganic species of different toxicity and the redox state speciation of multiply charged ions are discussed. The second part of the Minireview deals with the development and electroanalytical use of a new kind of nanostructured electrode, named nanoelectrode ensembles, which are prepared by template synthesis within the pores of microporous guest membranes. Advantages, peculiarities, and limits of such devices are discussed together with perspectives for their use in electroanalytical sensing at trace and ultratrace concentration levels in environmental samples.

Voltammetric determination of trace mercury in chloride media at glassy carbon electrodes modified with polycationic ionomers

Abstract The perfluorinated polycationic polymer Tosflex ® is used for preparing polymer modified electrodes able to preconcentrate and detect the anionic complex HgCl 2− 4 , which is the prevailing inorganic Hg(II) species in sea water and other chloride media. The study of the ion-exchange voltammetric behaviour of the tetrachloromercurate(II) complex at Tosflex-modified electrodes indicates the efficient incorporation of the analyte into the polymeric coating to which a remarkable positive shift in the reduction potential of HgCl 2− 4 to Hg 0 is associated. The partition and selectivity coefficient values for the ion-exchange equilibrium involved are calculated from voltammetric data. When using an ion-exchange preconcentration step under open circuit conditions followed by a cyclic voltammetry detection step, a detection limit in the 10 −8 M range is achieved, the exact figure depending on the scan rate employed. The application of a reducing potential during the preconcentration (i.e., using a mixed ion-exchange + Faradaic preconcentration regime) and the use of differential pulse voltammetry, lower the relevant detection limit by about three orders of magnitude. Results concerning optimization of the experimental parameters as well as lowering of the influence of possible interferents, such as copper and competing anions, are reported. Finally, an analytical procedure for exploiting the peculiar properties of Tosflex-modified electrodes for the determination of mercury in coastal waters samples is proposed and experimentally tested.

Ion-Exchange Voltammetry at Polymer Film-Coated Nanoelectrode Ensembles

Ensembles of nanoscopic disk-shaped electrodes have been shown to offer enhancements in electroanalytical detection limits relative to electrodes of macroscopic dimensions (e.g., disk electrodes with diameters of ∼1 mm). Enhancements in electroanalytical detection limits have also been observed at macroscopic electrodes that have been coated with films of ion-exchange polymers. In this paper we combine these two concepts. We demonstrate that a nanoelectrode ensemble (NEE) that has been coated with a thin film of the Kodak ion-exchange polymer AQ 55 shows enhanced electroanalytical detection limits relative to the uncoated NEE and to the coated macroscopic electrode. To our knowledge, this is the first investigation of the electrochemistry, and the electroanalytical advantages, of polymer film-coated NEEs.

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 1. Application to Wine

Differential-pulse anodic stripping voltammetry with a mercury microelectrode is used for the determination of zinc, cadmium, lead and copper in wine at its natural pH without pretreatment. The effects of the matrix on the stripping peaks are studied in detail by varying the concentration of the metals. Intermetallic (CuZn) interferences and the effects of oxygen are described. The results obtained for the labile metal contents varied from 2 μg l−1 for cadmium to 148 μg l−1 for zinc; standard addition plots were linear over about two orders of magnitude above these levels, demonstrating the negligible effect of organic matter. Acidification of the sample with hydrochloric acid to pH 1 allowed the total metal contents to be determined. The reliability of the method was tested by comparison with the results obtained with atomic absorption spectrometry; the differences were within 10–20%.

Nanoelectrode ensembles as recognition platform for electrochemical immunosensors

In this study we demonstrate the possibility to prepare highly sensitive nanostructured electrochemical immunosensors by immobilizing biorecognition elements on nanoelectrode ensembles (NEEs) prepared in track-etch polycarbonate membranes. The gold nanodisk electrodes act as electrochemical transducers while the surrounding polycarbonate binds the antibody-based biorecognition layer. The interaction between target protein and antibody is detected by suitable secondary antibodies labelled with a redox enzyme. A redox mediator, added to the sample solution, shuttles electrons from the nanoelectrodes to the biorecognition layer, so generating an electrocatalytic signal. This allows one to fully exploit the highly improved signal-to-background current ratio, typical of NEEs. In particular, the receptor protein HER2 was studied as the target analyte. HER2 detection allows the identification of breast cancer that can be treated with the monoclonal antibody trastuzumab. NEEs were functionalized with trastuzumab which interacts specifically with HER2. The biorecognition process was completed by adding a primary antibody and a secondary antibody labelled with horseradish peroxidase. Hydrogen peroxide was added to modulate the label electroactivity; methylene blue was the redox mediator generating voltammetric signals. NEEs functionalized with trastuzumab were tested to detect small amounts of HER2 in diluted cell lysates and tumour lysates.

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l−1 Cu, 0.38 μg l−1 Pb, 0.01 μg l−1 Cd and 0.95 μg l−1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.

Determination of mercury in process and lagoon waters by inductively coupled plasma-mass spectrometric analysis after electrochemical preconcentration: comparison with anodic stripping at gold and polymer coated electrodes

Abstract A combined electrochemical-inductively coupled plasma-mass spectrometry (EC-ICP-MS) method for the determination of trace mercury in water samples is presented. It takes advantage of the electrochemical preconcentration of mercury onto a gold spiral electrode followed by ICP-MS analysis after the electrochemical reoxidation of deposited mercury in pure supporting electrolyte. The advantages of the EC-ICP-MS approach with respect to conventional ICP-MS, are the increased sensitivity and the elimination of the effect of interfering substances eventually present in the sample. EC-ICP-MS is applied to the determination of nanomolar and subnanomolar concentrations of mercury(II) ions in real samples such as process waters (from a chlor-alkali plant) and lagoon waters (from Venice channels). Analytical performances obtained by EC-ICP-MS are discussed and compared with those obtained by anodic stripping voltammetry at gold and at Tosflex-coated glassy carbon electrodes.

Conical nanopore membranes: solvent shaping of nanopores

We have undertaken a systematic investigation of the influence of ethanol on the shape of conical pores produced by the track-etch technique in poly(ethylene terephthalate) films. We have found that the cone angle of the conical nanopore generated is dependent on the amount of ethanol present in an alkaline etching solution. By varying the percentage of ethanol in the etch solution, precise control over the geometry of the conical nanopore and nanomaterials templated within these pores can be attained. We prove this by plating gold nanocones within the various conical nanopores prepared, dissolving the membrane to liberate the nanocones, and imaging the nanocones using scanning electron microscopy. The results of these investigations are reported here.

Oxidation potentials of electrolyte solutions for lithium cells

Abstract The oxidation potentials, E ox , of several solutions of interest for nonaqueous Li cells have been measured by linear sweep voltammetric experiments. A correlation is found between E ox and the basicity of the solvents, expressed by their donor numbers (DN). Esters and sulfones have higher resistance to oxidation than ethers, which possess the highest DN values. All solutions have E ox > 4 V vs Li/Li + . However, some reactivity between positive electrodes and solutions has been observed below this potential.