University of North Florida
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Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Alain Walcarius

Abbrev:
Walcarius, A.
Other Names:
Address:
Laboratorie de Chimie Physique Pour L'Environnement, Unite Mixte de Recherche Umr 7564, CNRS - Universite H. Poincare Nancy I, 405, Rue de Vandoeuvre, F-54600, Villers-Les-Nancy , France
Phone:
+33-3-8391-6343
Fax:
+33-3-8327-5444

Citations 6

"Flow Injection Indirect Amperometric Detection Of Ammonium Ions Using A Clinoptilolite-modified Electrode"
Sens. Actuat. B 1999 Volume 56, Issue 1-2 Pages 136-143
A. Walcarius, V. Vromman and J. Bessiere

Abstract: A copper ion-doped clinoptilolite-modified carbon paste electrode was evaluated as an amperometric sensor for non-electroactive ammonium cations in flow injection analysis. The electrochemical activity of copper was prevented in electrolyte solutions containing size-excluded cations such as tetrabutylammonium, while the presence of non-size-excluded cations such as ammonium gave rise to appreciable responses. Consequently, the injection of ammonium samples at the electrode surface (into a carrier stream made of tetrabutylammonium bromide solution) resulted in peak currents proportional to the concentration of the analyte NH4+. After optimization of the experimental conditions, very reproducible results (standard deviations < 1%, n = 10) were obtained, linear calibration was achieved in the 2 X 10^-5 M to 1 X 10^-3 M concentration range, and the detection limit was 5 X 10^-6 M. The effect of interfering cations was also discussed and the sensors performance was evaluated for the analysis of ammonium in synthetic ground water.
Preconcentration

"Flow Injection Amperometric Detection At Enzyme-Modified Gold Nanoelectrodes"
Electroanalysis 2004 Volume 16, Issue 3 Pages 190-198
Marc Delvaux, Sophie Demoustier-Champagne, Alain Walcarius

Abstract: Gold nanotubular electrode ensembles were prepared by using electroless deposition of the metal within the pores of polycarbonate particle track-etched membranes. Glucose oxidase (Gox), used as a model enzyme, has been immobilized onto preformed self-assembled monolayers (mercaptoethylamine or mercaptopropionic acid) on electroless gold via cross-linking with glutaraldehyde or covalent attachment by carbodiimide coupling. Flow-injection analysis systems in flow-through or wall-jet configurations using these Gox-modified nanoelectrodes are described. The influence of different experimental parameters (i.e., applied potential, flow rate, interferents) on the analytical response of the sensor to glucose has been evaluated. Under optimized conditions, very reproducible results (standard deviations <4%, n=38) were obtained, linear calibration was achieved in the 2 x 10^-4 M to 3 x 10^-2 M concentration range and the detection limit was 2 x 10^-4 M. Moreover, no significant interferences from species like ascorbic and uric acids were observed at a potential of +0.9 V.

"Amperometric Detection Of Nonelectroactive Cations In Electrolyte-free Flow Systems At Zeolite Modified Electrodes"
Electroanalysis 1999 Volume 11, Issue 6 Pages 393-400
A. Walcarius, P. Mariaulle, C. Louis, L. Lamberts

Abstract: An electrochemical detector was designed and constructed, based upon a thin-layer cell with a working electrode prepared from carbon paste modified with copper-(or silver-) exchanged zeolite particles. This electrode was then evaluated as a sensor for nonelectroactive cations in an electrolyte-free flow injection system and as an amperometric detector for suppressed ion chromatography. In the absence of supporting electrolyte, a higher signal-to-background ratio enhanced by about two order of magnitude the response obtained in electrolytic medium. Peak currents resulted from an important faradic component which was due to the electrochemical activity of the mediator-containing zeolites, while the capacitive counterpart was much lower. When applied to the analysis of alkali, alkaline earth metal and ammonium ions, in combination with a suppressed ion chromatography system, the zeolite-modified detector gave rise to reproducible amperometric responses. This resulted in chromatograms comparable to those obtained simultaneously by using a conductivity detector in series, and any extra-column effects were never observed. The most sensitive responses were achieved when using zeolites displaying the largest pore size, the highest ion exchange capacity, and the most mobile mediator, to ensure the highest exchange rates for the analytes within the zeolite framework.

"Application Of Electrodes Modified With Ion-exchange Polymers For The Amperometric Detection Of Non-redox Cations And Anions In Combination To Ion Chromatography"
Electrochim. Acta 2001 Volume 46, Issue 23 Pages 3543-3553
P. Mariaulle, F. Sinapi, L. Lamberts and A. Walcarius

Abstract: An amperometric sensor for non-electroactive ions was designed, evaluated in flow injection analysis, and applied as a novel detector in suppressed ion chromatography. It consists of a carbon paste electrode modified with either a polycationic or a polyanionic polymer containing a suitable charge transfer mediator (Fe(CN)63- or Cu2+), operating in an indirect amperometric mode. The detection mechanism involves ion exchange between the non-redox ionic analyte and the electroactive mediator, in the polymer particles located at the electrode surface, followed by the electrochemical transformation of the mediator species leached out of the polymer at the electrode / solution interface. As detection was achieved in the absence of added supporting electrolyte, the amperometric signal contains both faradic and capacitive components. Optimization was performed to get the highest faradic signals, by varying various experimental parameters (i.e. applied potential, composition of the electrode). These systems were then successfully applied to the analysis of mixtures of cations (Li+, Na+, K+, NH4+, Ca2+, Mg2+) and anions (F-, Cl-, NO2-, NO3-, SO42-, PO43-) subsequent to chromatographic separation. Good operational stability was observed, with typically less than 5% signal loss for 50 successive measurements.

"Rate Of Access To The Binding Sites In Organically Modified Silicates. 1. Amorphous Silica Gels Grafted With Amine Or Thiol Groups"
Chem. Mat. 2002 Volume 14, Issue 6 Pages 2757-2766
Alain Walcarius, Mathieu Etienne, and Jacques Bessi&eagrave;re

Abstract: The speed at which selected reactants are reaching active sites grafted on porous silica gels of various nature and porosity was evaluated using some model systems: protonation of aminopropyl-grafted silica (APS), mercury(II) binding on mercaptopropyl-grafted silica (MPS), and accumulation of copper(II) on APS. Data were obtained from batch experiments, by monitoring the consumption of reactant in solutions containing the solid phases as dispersed particles (average size: 60-150 mum). Various grafted solids were studied, with pore diameter ranging between 4 and 15 nm and organic group contents of typically 1.4-1.9 mmol g-1. Diffusion processes in the porous organically modified silicas were found to be dramatically restricted as compared to those observed in homogeneous solution (approximate to10(3)-10(4) times slower). They were dependent on several factors such as the pore size of the material and the size of the reactant, the density of grafted organic sites, and the nature of the starting silica gel. Evaluation of apparent diffusion coefficients was achieved by applying a simplified model based on spherical diffusion. This has allowed us to point out a significant decrease in the access rates upon gradual completion of reactions: as the reactant concentration in the vicinity of increasing amounts of grafted groups is raised progressively, there is less room available in the porous structure to enable the probe to reach rapidly the remaining active sites. The apparent diffusion coefficient was found to drop dramatically after typically 30-50% reaction completion, depending on the nature of the probe. This study allows highlighting the optimal conditions that should be required to ensure efficient application of grafted silica gels, that is, in the fields of catalysis or heavy metal extraction.

"Factors Affecting The Analytical Applications Of Zeolite Modified Electrodes: Indirect Detection Of Nonelectroactive Cations"
Anal. Chim. Acta 1999 Volume 388, Issue 1-2 Pages 79-91
A. Walcarius

Abstract: Carbon paste electrodes modified with several types of copper-doped zeolites were evaluated as sensors for nonelectroactive cations in a flow injection system. After having described the amperometric detection mechanism and proposed an efficient procedure to achieve good reproducibility in successive measurements, it was shown how various experimental parameters influenced the quantitative determination of potassium ions (chosen as reference cationic species), such as the applied potential, mobile phase composition and flow rate, the ionic strength of the sample solution, or the injection volume. The analysis was then extended to other mono-and divalent cations and selectivity series were established in relation to wherever zeolites A, X, Y, or clinoptilolite was used. It was concluded that the sensors response was mainly governed by the diffusion of both the electron transfer co-factor (Cu2+ species) and the cationic analytes, rather than by the thermodynamic predictions related to ion exchange equilibrium despite the fact that the amperometric detection was allowed to occur only after the exchange of Cu2+ species for the cationic analyte. Detection limits around 10^-6 M were obtained for the analysis of alkali metal, ammonium, calcium and magnesium ions using the copper-doped zeolite Y modified electrode in a 0.01 M tetrabutylammonium bromide mobile phase.
Potassium Metals, alkali Ammonium Calcium Magnesium Electrode Amperometry Optimization Ionic strength Detector Apparatus