A Simple Method for Construction of Flexible, Subminiature Ion-Selective Electrodes

Abstract

ABSTRACT Liquid membrane electrodes have greatly facilitated the measurement of pH and ion activities in intra- and extracellular fluids. Ion-selective microelectrodes (ISMEs) can be constructed by introducing a short column of a neutral carrier or ion-exchanger cocktail into the tip of a glass micropipette. The inner surface of the glass is first made hydrophobic by exposure to compounds containing silane (Thomas, 1978; Amman, 1986). This process, termed silanization, prevents subsequent displacement of the hydrophobic cocktail, either by entry of aqueous biological fluids through the tip of the micropipette or by migration of the backfilling solution. Macroscopic electrodes (5–10 mm diameter) can be produced by first incorporating appropriate neutral carriers into solvent polymeric membranes of polyvinyl chloride (PVC) or silicone rubber. Membranes can then be stamped out with a cork borer and glued or fused onto PVC tubing or commercially available electrode bodies (Meier et al. 1980). Electrodes with outer diameters of 1.5–1.7 mm have been formed by dipping tubing into a cocktail containing the ionophore, PVC and solvents. Solvent evaporation forms a membrane about 25 μm thick on the tip of the tubing (Oesch et al. 1987). A technique for the construction of miniature double-barrelled K+ electrodes with a total o.d. of 600 μm and a shank 1.3 cm long has been described by Hill et al. (1978).