This invention relates to methods for reducing the presence of a compound in an ionically conductive material, e.g., for use in iontophoretic devices, wherein the presence of the compound interferes with detecting a selected analyte. Removal of the compound can typically take place either during or after the manufacture of the ionically conductive material or an assembly comprising this material. Also disclosed are methods for generating selectively permeable barriers on the reactive faces of electrodes. Further, this invention relates to hydrogels comprising one or more biocides, as well as assemblies containing such hydrogels.