Spatially Averaging Electrodes

Abstract

Both potentiometric and voltammetric measurements report on the concentration of the analyte in the closest layer of the sample solution that is unperturbed by the measurement. Besides this local concentration, the solution composition within the thin boundary layer adjacent to the electrode|solution interface is influenced also by local mass transport and other electrochemical processes necessary for signal transduction. This local perturbation of concentrations is typically corrected for by calibration so that the ultimate output of the measurement is the local concentration, at a distance of a few micrometers to about 100 microm from the electrode surface. In contrast to many optical techniques, the electrochemical approach is therefore only capable of measuring local concentrations but cannot be used to assess three-dimensional (3D)-averaged bulk concentrations of inhomogeneous samples. This may pose a problem in very small samples where homogenization by stirring is difficult. We present here the concept of spatially averaging electrodes that can, due to their special design, report 3D spatially averaged bulk concentration of inhomogeneous samples that have some type of symmetry. Within a given type of symmetry an infinite variation of concentration distribution may exist. We illustrate the concept of spatially averaging electrodes with results obtained in microliter-sized hemispherical samples with a source in the center of the drop.

Electrochemical Sensors

“…Sheth and co-workers reported a concept for estimating the bulk concentration of analytes in small inhomogenous samples that cannot be stirred (58). The authors proposed a spatially averaging electrode that utilizes a 2D spiral shape capable of determining the 3D bulk concentrations.…”

A Novel Electrochemical Sensor for the Detection of Reactive Red Dye to Determine Water Quality

“…Nonuniform ohmic drop on an electrochemical transducer significantly affects the cyclic voltammogram data. The shape of the cyclic voltammograms predicts various electrochemical transducer geometries and experimental conditions [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

Spatially Averaging Electrodes

“…Inhomogeneous concentration distribution of H + /OH -ions develops in samples that are about 5µL or larger in volume despite their high diffusion rate, as seen in diffusional microtitration (1,2). To address this issue, we have developed and tested a novel design of electrodes that we call spatially averaging electrodes, SAE, that can report 3D spatially averaged bulk concentrations of inhomogeneous samples without the need for stirring (3). In this manuscript we discuss the theory and some possible geometries of SAEs designed for two different types of symmetric inhomogeneity, hemispherical and cylindrical.…”