Ramon Oliver

Degradation of atrazine by electrochemical advanced oxidation processes using a boron-doped diamond anode.

Solutions of 30 mg L(-1) of the herbicide atrazine have been degraded by environmentally friendly electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) using a small open and cylindrical cell with a boron-doped diamond (BDD) anode. AO has been carried out either with a stainless steel cathode or an O(2) diffusion cathode able to generate H(2)O(2). Hydroxyl radicals ((*)OH) formed at the BDD surface in all EAOPs and in the bulk from Fentons reaction between added Fe(2+) and electrogenerated H(2)O(2) in EF and PEF are the main oxidants. All treatments yielded almost overall mineralization, although the rate for total organic carbon (TOC) removal is limited by the oxidation of persistent byproducts with (*)OH at the BDD surface. In AO, TOC abatement is enhanced by parallel electrochemical reduction of organics at the stainless steel cathode, while in PEF, it also increases from additional photolysis of intermediates by UVA light under the synergistic action of (*)OH in the bulk. The effect of current and pH on the degradative behavior of EAOPs has been examined to determine their optimum values. Atrazine decay always follows a pseudo-first-order reaction, being more rapidly destroyed from (*)OH in the bulk than at the BDD surface. Aromatic intermediates such as desethylatrazine, desethyldesisopropylatrazine, and cyanuric acid and short linear carboxylic acids such as formic, oxalic, and oxamic have been identified and quantified by reversed-phase and ion-exclusion HPLC, respectively. Released inorganic ions such as Cl(-), NO(3)(-), and NH(4)(+) have been followed by ionic chromatography.

Cellular Adhesion, Proliferation and Viability on Conducting Polymer Substrates

This work reports a comprehensive study about cell adhesion and proliferation on the surface of different electroactive substrates formed by pi-conjugated polymers. Biological assays were performed considering four different cellular lines: two epithelial and two fibroblasts. On the other hand, the electroactivity of the three conducting systems was determined in physiological conditions. Results indicate that the three substrates behave as a cellular matrix, even though compatibility with cells is larger for PPy and the 3-layered system. Furthermore, the three polymeric systems are electro-compatible with the cellular monolayers.

Mineralization of desmetryne by electrochemical advanced oxidation processes using a boron-doped diamond anode and an oxygen-diffusion cathode.

The mineralization of acidic aqueous solutions of the herbicide desmetryne has been studied by electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation with electrogenerated H(2)O(2) (AO-H(2)O(2)), electro-Fenton (EF) and photoelectro-Fenton (PEF) with UVA light. Electrolyses were conducted in an open and cylindrical cell with a boron-doped diamond (BDD) anode and an O(2)-diffusion cathode for H(2)O(2) generation. The main oxidizing species are ()OH radicals formed at the BDD surface in all treatments and in the bulk from Fentons reaction between added Fe(2+) and electrogenerated H(2)O(2) in EF and PEF. A poor mineralization was attained using AO-H(2)O(2) by the slow oxidation of persistent by-products with ()OH at the BDD surface. The synergistic action of ()OH in the bulk enhanced the degradation rate in EF, although almost total mineralization was only achieved in PEF due to the additional ()OH generation and photolysis of intermediates by UVA irradiation. The effect of current, pH and herbicide concentration on the mineralization degree and mineralization current efficiency of each EAOP was examined. Desmetryne decay always followed a pseudo first-order kinetics, being more rapidly destroyed in the sequence AO-H(2)O(2)<EF<PEF. In all EAOPs, ammeline and cyanuric acid were identified as persistent heteroaromatic by-products and oxamic and formic acids were detected as generated carboxylic acids. The generation of cyanuric acid mainly by oxidation with ()OH at the BDD surface is the predominant path for desmetryne degradation. The initial nitrogen of desmetryne yielded NO(3)(-) ion in low proportion and NH(4)(+) ion in much lesser extent, suggesting that its major part was lost as volatile N-derivatives.

Determination of polyphenols in wines by liquid chromatography with UV spectrophotometric detection

This paper describes a new chromatographic method for the determination of polyphenolic compounds in wines. The method is based on the separation of analytes by reversed-phase mode in a C18 column (2.6 μm particle size) and UV absorption spectroscopy. The elution gradient is generated from 0.1% formic acid aqueous solution and acetonitrile as an organic modifier. Experimental conditions including pH, percentage of organic modifier and elution gradient profile have been thoroughly optimized using experimental design. A multi-objective function has been defined as a criterion for obtaining a satisfactory compromise among number of compounds separated, resolution and analysis time. Multi-detection at 280, 310 and 370 nm has been utilized in order to work under the most appropriate wavelengths for each compound. Figures of merit including linearity ranges, precisions, detection limits and recoveries have been established under selected experimental conditions using synthetic standards and commercial red wines. The method has been applied to analyze red wines from various Spanish regions.

Electropolymerization of 2,5-di-(-2-thienyl)-pyrrole in ethanolic medium. Effect of solution stirring on doping with perchlorate and chloride ions

Abstract The electrochemical behavior of 2,5-di-(-2-thienyl)-pyrrole (SNS) on Pt has been studied from a 10 mM monomer solution in 0.2 M LiClO 4 +ethanol or in 0.2 M LiCl+ethanol by cyclic voltammetry, chronopotentiometry and chronoamperometry. The monomer exhibits two similar consecutive oxidation processes. Uniform, adherent and electroactive films of dark-blue poly(SNS) doped with ClO 4 − or with Cl − are obtained at low potentials related to the first process. Reproducible film weights are found at 0.700 V versus Ag|AgCl during 360 s. The increase in transport rate of reactants by stirring the solution with a magnetic bar at 150 rpm accelerates the SNS electropolymerization, allowing to collect much more polymer weight than from the quiescent solution. The productivity of poly(SNS) doped with Cl − determined by ‘ex situ’ ultramicrogravimetry increases notably under stirring, although its percentage in Cl − is similar to that found under quiescent conditions. This is ascribed to the production of a major proportion of longer linear molecules in polymer, consistent with its higher conductivity when it is synthesized under stirring. This effect is not so clear for the poly(SNS) doped with ClO 4 − due to the little influence of stirring upon its productivity and conductivity. The detection of short linear oligomers in the soluble fractions of polymers in thioglycerol by mass spectrometry-fast atom bombardment allows to propose a radical polycondensation as initial electropolymerization mechanism.

Determination of HIV drugs in biological matrices: A review

The present paper reviews the recent advances on the determination of antiretroviral drugs against the human immunodeficiency virus (HIV). Methods have been reviewed with special emphasis on the principal analytical strategies for dealing with clinical samples as well as the determination of the newest drugs. The most critical steps of the analytical procedures including the sample treatment, separation and validation have been discussed. Finally, a brief description of representative applications is given.

Reversed-phase liquid chromatographic method with spectrophotometric detection for the determination of antiretroviral drugs

In the present paper, a new chromatographic method for the determination of acquired immune deficiency syndrome (AIDS) drugs in plasma samples is proposed. The method consists of solid-phase extraction for sample pretreatment and further chromatographic analysis. Drugs have been separated on a C(18) column using an elution gradient based on an increase in the acetonitrile percentage. Analytes have been detected spectrophotometrically at 240, 250, 260 and 280nm. Chromatographic conditions have been thoroughly optimized using experimental design and multicriteria functions. Analytical parameters of the method have been established for both synthetic and plasma samples. Limits of detection are around 5ngmL(-1) for reverse transcriptase inhibitors (nucleoside and non-nucleoside) and 20ngmL(-1) for protease inhibitors. The method has been validated through a spiking/recovery procedure at three concentration levels. Results obtained are highly satisfactory, with recovery values around 100% for all drugs. The method has been applied to the determination of various drug mixtures of medical interest in plasma samples.

Electrochemical Behavior of the Cd(II)/Cd(Hg) System in Aqueous Mixtures of Diols and Triols

The electrochemical behavior of the Cd(II)/Cd(Hg) couple (Cd(II) concentration ) in aqueous mixtures of 1,4‐butanediol (BD) and glycerol (GL) containing has been studied. The reversible half‐wave potentials, the diffusion coefficients, and the Walden products for Cd(II) have been determined by polarography, whereas the diffusion coefficient of Cd in mercury, the transfer coefficient for Cd(II) electroreduction, and the apparent standard rate constants have been obtained by cyclic voltammetry. The standard free energies of transfer of 1 mole of Cd(II) ions from water to BD‐water and to GL‐water mixtures are found to be always negative, indicating a higher stability of Cd(II) in organic‐aqueous mixtures than in pure water. The break‐up of these values into electrostatic and chemical contributions shows that all organic‐aqueous mixtures used here are more basic than pure water, and that Cd(II) solvation increases with the mole fraction of BD or GL. The structural properties of the liquid mixtures are analyzed using the Walden products at different BD or GL levels. The changes in the kinetics of the Cd(II)/Cd(Hg) system with solvent composition are discussed in terms of existing models. Results obtained are compared with those previously reported in aqueous mixtures of ethylene glycol and 1,2‐propanediol.

Medium effect on the electrochemical behaviour of the Zn2+/Zn(Hg) system in aqueous 1,2-propanediol solutions

The electrochemical behaviour of the Zn2+/Zn(Hg) couple has been studied in aqueous mixtures of 1,2-propanediol (PD) containing 5.0 × 10−2 mol dm−3 LiClO4 as background electrolyte by polarography and cyclic voltammetry. The reversible half-wave potentials, the diffusion coefficients and the Walden products for Zn2+, as well as the transfer coefficients and the apparent standard rate constants for the Zn2+/Zn(Hg) system, were determined. The standard Gibbs energies of transfer of 1 mol of Zn2+ ions from water to PD-water mixtures (ΔG0t) were calculated from the reversible half-wave potentials referred to the Fic+/Foc scale and their values were always negative, indicating a higher stability of Zn2+ in aqueous PD solutions than in pure water due to the preferential solvation of Zn2+ by PD. The analysis of the variation of the Walden product with solvent composition indicates an enhancement of the solvent structure in the water-rich region. It was found that the changes in the kinetics of the Zn2+/Zn(Hg) system with PD mole fraction depend mainly on the surface phase composition. The mechanism of the cathodic and anodic processes of this system under irreversible conditions is discussed.