Nitrate ion selective electrode

An electrode for measuring the concentration of nitrate ions in aqueous solutions comprising a container embodying an internal reference system and a non-porous polymer membrane mounted upon said container, said membrane comprising a combination of an electroactive material, a solvent and a non-porous polymeric membrane matrix material;

• wherein said electroactive material is organic nitrate ion sensitive and comprises a quaternary ammonium salt selected from the group consisting of:
• tetraoctyl ammonium nitrate, tetranonyl ammonium nitrate, tetradecyl ammonium nitrate, tetraundecyl ammonium nitrate, tetradodecyl ammonium nitrate, tetratridecyl ammonium nitrate and tetratetradecyl ammonium nitrate;
• wherein the solvent is a liquid of substantial viscosity and is a solvent for said quaternary ammonium salt, said solvent consisting of a dialkylphthalate or a dialkyladipate of a solubility parameter of 9 .+-. 2 (cal/cm.sup.3).sup.1/2 and being substantially organophilic and hydrophobic;
• and wherein the polymer membrane matrix material is a non-porous polymer membrane matrix material selected from the group consisting of polyvinylchloride and polyurethane.