Individually addressable gel-integrated voltammetric microelectrode array for high resolution measurement of concentration profiles at interfaces

The application of a novel voltammetric probe, based on an individually add ressable gel-integrated microelectrode array (IA-GIME), for real-time, high -spatial resolution concentration profile measurements at interfaces is des cribed. Reliability and validity of steep metal concentration gradients obt ained with this novel system have been demonstrated by performing systemati c tests,at-well-controlled liquid-liquid and liquid-solid interfaces. The L iquid-liquid interface was formed by two layers of aqueous solutions with d ifferent components; only one layer contained trace metal ions (Pb(II) and Cd(II)); the individually addressable microelectrode array was placed at th e interface of the liquid-liquid system; the concentration profiles were re corded as function of time; and the effective diffusion coefficients were c alculated. The liquid "solid" interface was formed from an aqueous solution layer overlying a bed of silica particles saturated with an aqueous soluti on. The sensor array has been used to monitor the diffusion processes of Tl (I) or Pb(II) from the liquid phase to the "solid" phase. The influences of porosity, geometry of the porous media, and complexation between metal ion and silica, on the diffusion processes, have been studied. All these resul ts show that correct diffusion profiles of metal ions at interfaces can be obtained with 200-mum resolution with the IA-GIME, They also demonstrate th at, for measurements in "solid" phase, the aforementioned factors must be c onsidered carefully for correct calibration of any electrodes and the gel-i ntegrated microelectrodes are unique tools to enable calibration of the sen sors with synthetic solutions.