Miniaturized reference electrodes. II. Use in corrosive, biological, and organic media

In a recent paper [9] we reported the manufacturing and performance of miniaturized reference electrodes (MREs) with low sensitivity to chloride ions and pH. Here, we demonstrate the wide range applicability of a MRE based on an Ag/Ag2S internal reference element (IRE), imbedded in a photopolymerized hydrogel of improved composition, which contains the supporting electrolyte. Exchange current density, temperature coefficient, impedance value, and the voltammetric and potentiometric use of the Ag/Ag2S-based MRE are discussed relative to the previously reported Ag/AgSCN, Ag/Ag3PO4, and Ag/AgCl-based MREs. No special or extensive conditioning is required when moving these MREs from aqueous supporting electrolyte to an organic solution or from one organic medium to another, and the equilibration time in a new medium is very rapid (< 6 min). The new Ag/Ag2S MRE has a highly stable potential in various media, including aqueous solutions (salt buffers and 20 wt.% H2SO4), biological samples (bovine serum albumin), mixed aqueous-organic, and organic supporting electrolytes (methanol, ethanol, acetonitrile, propylene carbonate, methylene chloride, and DMSO). This is particularly advantageous when in the course of the electrochemical analysis an organic solution is being added to an aqueous supporting electrolyte. Such MREs are suitable for analyses of muL sample volumes and for use in protein-containing media.