Spatially averaging electrodes.

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.