Antifouling Membrane-Covered Voltammetric Microsensor for in Situ Measurements in Natural Waters

Abstract

A novel, effective, antifouling membrane-covered voltammetric microsensor has been developed. It combines the unique properties of microelectrodes and diffusion in gels. An agarose gel, with thickness varying in the range 0.4−0.9 mm, is used as the membrane and acts as a dialysis membrane, i.e. allows diffusion of small ions and molecules and retains colloidal materials. The voltammetric microelectrode measures the test compounds within the gel after equilibration. Diffusion of ions through various types of gels has been investigated by diffusion cell, square wave cathodic sweep voltammetry (SWCSV), and square wave anodic stripping voltammetry (SWASV) to characterize the diffusion properties of the agarose gel membranes. These studies revealed that (i) the agarose gel used is totally inert toward target compounds and (ii) the anticonvection properties of the agarose gel ensure purely diffusion-controlled transport within the membrane. Diffusion coefficient values of ions in the agarose membrane were found to be lower than those in free solution. Considering the inertness of the agarose gel used toward the ions measured, this discrepancy can be ascribed to the intrinsic physical properties of the agarose gel which influence the ion mobility. Reproducible values have been obtained for equilibration times and diffusion coefficients for gels prepared under controlled conditions with a given type and concentration of agarose. The agarose membrane-covered, Hg-plated, Ir-based microelectrode (μ-AMMIE) was applied to lead and cadmium analysis by SWASV in the presence of 10−31 mg/L of fulvic and humic compounds and in raw river waters containing high concentrations of suspended matters (50−78 mg/L). Results of these measurements under such drastic conditions confirm the efficiency of the agarose gel membrane against adsorption of organic and inorganic matters on the Hg surface of the voltammetric microsensor. Thus, these results demonstate that direct measurements of analytes in complex media can be made with μ-AMMIE without physical and chemical interferences of the test solution, in particular due to the relatively large gel thickness compared to the diffusion layer thickness of the microelectrode and of the properties of the agarose gels used.

Integrated Microanalytical System for Simultaneous Voltammetric Measurements of Free Metal Ion Concentrations in Natural Waters

“…The average currents for Cu(II), Pb(II) and Cd(II) over the five day measurement period were respectively 221, 211 and 212 nA with relative standard deviations of 9%, 8% and 5% (N ¼ 15). These results show that, as for the GIME [16,24], continuous CGIME measurements without sensor maintenance, can be performed over several days with a good precision.…”

“…Thus equilibrium between bound and free form in solution remains virtually undisturbed. Interference of the matrix on the metal accumulation, due in particular to the fouling of the chelating resin, does not occurs as colloidal/particulate matters are efficiently excluded from the agarose gel [13,16,17]. Under these conditions, it is expected that: i) each metal will accumulate on the resin in proportion to their free ion concentrations in the sample; ii) the free ion concentrations of the target metals in solution can be determined from SWASV signal measured in step 3) using a calibration curve established, at a fixed sensor/sample equilibration time, in pure electrolyte spiked with various amount of trace metals.…”

Coeficientes de difusão de metais em materiais não convencionais (agarose e acetato de celulose) usados na técnica de difusão em filmes finos por gradientes de concentração

“…20 Valores dos coeficientes de Cd(II) e Cu(II) em agarose 1,5% (m/v) próximos aos valores encontrados na água foram relatados em trabalhos anteriores. 20 Por outro lado, outros autores 23 Todos os valores dos coeficientes de difusão encontrados foram inferiores aos valores relatados para água. 24 Para os íons Ba(II) e Mg(II), a redução foi mais acentuada, chegando em média a 80%.…”

Ultrasonically Enhanced Voltammetric Analysis and Applications: An Overview

“…These include preelectrolysis [119], wet ashing [120], UV digestion [121], and the addition of ethanolic suspension of fumed silica [122]. The effect of the surfactants has been partially surmounted by covering the working electrode with a permselective/ protective film such as Nafion, [123] agar [124], cellulose acetate [125] or polypyrole [116]. Such use allows the passage of the analytes to the electrode while restricting the access of surface-active compounds and has been reported to improve the analytical signal in stripping analysis [116,117,124,126] with analysis in the presence of up to10 ppm of a non-ionic surfactant [117].…”