Sol-gel modification of pH electrode glass membranes for sensing anions and metal ions

To obtain glass membrane electrodes selective for anions and metal ions, pH electrode glass membranes were modified by a sol-gel method using a quater nary ammonium salt and a bis(crown ether). A chloride ionsensing glass memb rane was designed, in which a pH electrode glass membrane was modified chem ically by an alkoxysilyl quaternary ammonium chloride. X-ray photoelectron spectroscopy confirmed the chemical bonding of the quaternary ammonium moie ty to the starting glass surface, which afforded the first example of glass -based "anion"-sensing membranes. A neutral carrier-type sodium ion-selecti ve glass membrane was also fabricated which encapsulates a bis(12-crown-4) derivative in its sol-gel-derived surface. Both sol-gel-modified anion and metal ion-selective glass electrodes exhibited high sensitivity to their io n activity changes. The present sol-gel modification paves the way for desi gning glass-based ion sensors with tailor-made ion selectivities toward ani ons as well as cations.