The hydrogen-ion selective glass electrode.

The properties and mechanism of operation of hydrogen-ion selective glass electrodes are reviewed and a model using information from recent research is presented. In the gel layer of a pH-glass protons or hydronium ions are bound to negative charges in a silicon network cross-linked with bi- or tervalent metal ions. The composition of the gel layer is discussed; it is known that the outer part contains water. The formation of a gel layer and its destruction in alkaline solutions are discussed. Between the gel layer and the dry glass there is a transition layer characterized by a very high resistivity. This forms a barrier to ion transport and prevents rapid corrosion of the glass. The ionic mobilities of various ions change drastically with distance inwards towards the dry glass. The alkaline and acid errors are discussed as well as the asymmetry potential. By etching away the gel layers and the transition layers on both sides of the glass and then starting hydration simultaneously on both sides, two symmetric layers can be produced. This will result in an almost complete cancellation of the asymmetry potential. Some applications to precision measurements and measurement in non-aqueous solvents are discussed.