Grégoire Lagger

Facilitated ion transfer reactions across oil|water interfaces : Part II. Use of the convoluted current for the calculation of the association constants and for an amperometric determination of the stoichiometry of MLjz+ complexes

Cyclic voltammetric experiments for reversible ion transfers across the aqueous/organic interface facilitated by a neutral macrocyclic ligand are presented for complexation reactions of 1:1 to 1:4 ion-to-ligand stoichiometries. The convoluted current is taken into account to derive general theoretical equations relating the half-wave potential to the initial concentrations of both the metal Mz+ and the ligand L. Analytical relationships are obtained for both limiting cases of ligand and, respectively, metal excess and for any type of reaction mechanisms. Likewise, considerations on the convoluted current provide a condition on the transition point between the diffusion regimes where either the metal or the ligand limits the transfer, which constitutes an amperometric determination of the complex stoichiometry. It is shown that the half-wave potential depends on the various over-all association constants, on the partition coefficient of the ligand and on the initial concentrations of both Mz+ and L. This dependence is the same for the TIC, TOC and TID mechanisms, but differs in the case of the ACT mechanism. The theoretical predictions are corroborated by the results deduced from various calculated voltammograms and are verified experimentally for the transfer of Pb2+ assisted by the thioether ligand 1,4,7,10-tetrathiacyclododecane at the water/1,2-DCE interface. Thanks to the simulation, it is shown that the experimental current waves are due to 1:1 and 1:2 complex formation and that the first association constant in the organic phase is log K-1(0) approximate-to 5

Electrochemical extraction of heavy metal ions assisted by cyclic thioether ligands

Abstract The ion transfer characteristics of a series of divalent heavy metal species have been studied at the polarised water|1,2-dichloroethane interface. Both direct and cyclic thioether assisted transfer mechanisms have been investigated by voltammetric measurements. Half-wave potentials and Gibbs energies for direct ion transfer processes follow the order, Pb2+

Biomarkers of oxidative stress and its association with the urinary reducing capacity in bus maintenance workers

BackgroundExposure to particles (PM) induces adverse health effects (cancer, cardiovascular and pulmonary diseases). A key-role in these adverse effects seems to be played by oxidative stress, which is an excess of reactive oxygen species relative to the amount of reducing species (including antioxidants), the first line of defense against reactive oxygen species. The aim of this study was to document the oxidative stress caused by exposure to respirable particles in vivo, and to test whether exposed workers presented changes in their urinary levels for reducing species.MethodsBus depot workers (n = 32) exposed to particles and pollutants (respirable PM4, organic and elemental carbon, particulate metal content, polycyclic aromatic hydrocarbons, NOx, O3) were surveyed over two consecutive days. We collected urine samples before and after each shift, and quantified an oxidative stress biomarker (8-hydroxy-2-deoxyguanosine), the reducing capacity and a biomarker of PAH exposure (1-hydroxypyrene). We used a linear mixed model to test for associations between the oxidative stress status of the workers and their particle exposure as well as with their urinary level of reducing species.ResultsWorkers were exposed to low levels of respirable PM4 (range 25-71 μg/m3). However, urinary levels of 8-hydroxy-2-deoxyguanosine increased significantly within each shift and between both days for non-smokers. The between-day increase was significantly correlated (p < 0.001) with the concentrations of organic carbon, NOx, and the particulate copper content. The within-shift increase in 8OHdG was highly correlated to an increase of the urinary reducing capacity (Spearman ρ = 0.59, p < 0.0001).ConclusionsThese findings confirm that exposure to components associated to respirable particulate matter causes a systemic oxidative stress, as measured with the urinary 8OHdG. The strong association observed between urinary 8OHdG with the reducing capacity is suggestive of protective or other mechanisms, including circadian effects. Additional investigations should be performed to understand these observations.

Amperometric tape ion sensors for cadmium(II) ion analysis

This paper describes a novel tape platform ion sensing methodology specific to the detection of cadmium(II) ions in aqueous solution based on assisted ion transfer reactions across a polarized water/organic gel micro-interface. The tape ion sensors were constructed to incorporate the micro-water/polyvinylchloride-2-nitrophenylethyl ether (PVC-NPOE) gel interfaces referred to as ionodes. The sensors have overall thicknesses less than 300 microm, allowing their packaging in a disposable tape format. The detection methodology is based on the selective assisted transfer of the cadmium ion in aqueous phase by ETH 1062 present in the PVC-NPOE gel layer and was first investigated using cyclic voltammetry. Quantitative analysis of cadmium(II) ions in aqueous solution using the tape sensors was then conducted under stop-flow conditions. Detection limits as low as 20 ppb (178 nM) for Cd(II) ions in very small volumes as low as a single 20 microl droplet without any sample preconcentration was achieved in an analysis time of approximately 20s, which could be easily employed for the direct measurement of Cd(II) ion levels in various field applications. The tape ion sensor can also be used in a flow-cell geometry to preconcentrate Cd(II) ions from aqueous samples and further improve the detection limit.

Excimer laser-induced electrochemical activity in carbon ink films

The effects on the microscopic and electrochemical properties of composite ink films after exposure to UV radiation from a 193 nm excimer laser source were investigated. The work considered two carbon ink types, a commercial screen ink material and a preparation consisting of micro-spherical glassy carbon with polystyrene. A scanning electron microscopy study of these ink film surfaces has concluded that laser treatments selectively etch the organic binding polymer from the composite surface thereby exposing sub-layers of carbon particulates. The photoablative processes by which the UV radiation interacts with materials not only remove the ink polymer, thereby increasing the surface area, but also chemically modify the carbon surface resulting in an increased rate of electron transfer. The cyclic voltammetric characteristics of potassium hexacyanoferrate(III) and ferrocene carboxylic acid at these modified ink films are analysed using the methodology proposed by Amatore et al. (J. Electroanal. Chem, 147 (1983) 39).

Contact Galvani potential differences at liquidjliquid interfaces Part II. Contact diffusion potentials in microsystems

The purpose of this work is to study diffusion potentials (i.e., liquid junction potentials) established between two static or flowing solutions in microsystems. One of the motivations of investigating the diffusion potential distribution is to be able to establish a potential gradient in a cell without introducing electrodes and using a potentiostat. By using finite element simulations, different geometries (i.e., microhole, Y-channel mixing and microtube injection) have been studied numerically. The calculations have allowed systematic studies of the influence of concentration ratio, flow rate and detector position. It is shown that the diffusion potential can be a useful way to quantify the degree of mixing or filling of solutions in microsystems. The theoretical part has been corroborated by experimental measurements of potential differences across a parallel flow channel, taking into account the diffusion potential and differences in the electrode potentials. It is apparent that the theoretical model gives a good fit to the experimental results.

Micro-glassy carbon inks for thick-film electrodes

Reference LEPA-ARTICLE-1997-016View record in Web of Science Record created on 2005-11-07, modified on 2017-05-12

Mercury Free Determination of Lead by Differential Pulse Anodic Stripping Voltammetry onto Silver Plated Rotograved Carbon Electrodes

Reference LEPA-ARTICLE-2001-019doi:10.1002/1521-4109(200102)13:2 3.0.CO;2-IView record in Web of Science Record created on 2005-11-07, modified on 2017-05-12

Hydro-voltaic cells. Part I. Concentration cells

The diffusion potential differences established between two laminar flows of electrolyte solutions of different concentrations are exploited to generate an electric current. It is shown that when a single redox couple is present in two flowing electrolyte solutions, the diffusion potential difference can induce a redox reaction at electrodes placed on the opposite walls of the cell, the electrical current being extracted in an external circuit. This hydro-voltaic cell operates solely on a salt concentration gradient and a hydrodynamic flow. In this work, we have investigated the influence of the salt concentration gradient and the concentration of the redox couple on the generated power.

Rotograved Carbon Electrodes for Amperometric Cadmium and Lead Determination

Reference LEPA-ARTICLE-1999-023doi:10.1016/S0022-0728(99)00226-0View record in Web of Science Record created on 2005-11-07, modified on 2017-05-12