Ion-Selective Electrodes With Sensing Membranes Covalently Attached to Both the Inert Polymer Substrate and Conductive Carbon Contact

The use of solid-contact ion-selective electrodes (ISEs) is of interest to many clinical, environmental, and industrial applications. However, upon extended exposure to samples and under thermal and mechanical stress, adhesion between these membranes and underlying substrates often weakens gradually. Eventually, this results in the formation of a water layer at the interface to the underlying electron conductor and in delamination of the membrane from the electrode body, both major limitations to long-term monitoring. To prevent these problems without increasing the complexity of design with a mechanical attachment, we use photo-induced graft polymerization to simultaneously attach ionophore-doped crosslinked poly(decyl methacrylate) sensing membranes covalently both to a high surface area carbon as ion-to-electron transducer and to inert polymeric electrode body materials (i.e., polypropylene and poly(ethylene-co-tetrafluoroethylene)). The sensors provide high reproducibility (standard deviation of E⁰ of 0.2 mV), long-term stability (potential drift 7 μV h⁻¹ over 260 h), and resistance to sterilization in an autoclave (121 °C, 2.0 atm for 30 min). For this work, a covalently attached H⁺ selective ionophore was used to prepare pH sensors with advantages over conventional pH glass electrodes, but similar use of other ionophores makes this approach suitable to the fabrication of ISEs for a variety of analytes.