The centenary of glass electrode: from Max Cremer to F. G. K. Baucke

Abstract

More than 100 years passed since 1906 when M. Cremer has measured for the first time the emf which builds up when two aqueous solutions with different acidity or alkalinity are separated by a thin glass membrane and since 1909 when F. Haber and Z. Klemensiewicz have obtained acid–base titration curves with the help of this device, thereby developing the glass electrode (GE) as an analytical tool. Twenty years later рН measurements with GEs became one of the most frequently performed procedures in research and industrial laboratories, in medicine, biology, agriculture, etc. That happened thanks to the progress made in measuring techniques and also in the development of special glasses. The latter, in turn, was a consequence of studying the dependence of electrode properties of glasses on their composition. That also resulted in the development of glasses for GEs having sensitivities toward M⁺ ions (Nа⁺, K⁺, Аg⁺, etc.) and glasses for measuring redox potentials. The data on the properties of GEs accumulated in the twentieth of last century formed the sound basis of the theory of glass electrodes. B.P. Nikolskii’s thermodynamic ion exchange theory has gained general recognition since 1937. Nikolskii's equation is widely used for the description of behavior not only of GEs but also of other ion-selective electrodes. Two approaches are distinguished in the evolution of the theory: one that is based on the assumption on the non-ideality of a glass membrane (Izmailov et al., Lengyel et al., Schwabe et al., Eisenman, and others) and the other approach based on the concept of various ionogenic groups in glass and their dissociation (Nikolskii, Schultz, and their colleagues, later Buck and Morf). The understanding of the potential of a glass electrode as an interfacial potential was replaced by the idea of a membrane potential, i.e., a potential drop including two interfacial potential drops and two diffusion potentials (Eisenman, Nikolskii's school, Doremus, etc.). The equilibrium at the boundary which determines the interfacial potential specifies the boundary conditions for the diffusion potential. The electrode properties of the glasses (the extension and slope of electrode function, its selectivity, etc.) in many respects depend on the mobilities of ions and the mechanism of their transport in the glass. A deeper insight into the functioning of the glass electrode was achieved by studying concentration profiles of ions in the glass layers which were altered by interaction with a solution, especially in combination with studies of the chemical and electrochemical processes on the glass/solution boundary, the dynamics of the GE potential, and the other properties of the glass surface. Dr. F.G.K. Bauke has made a significant contribution to GE studies. Using high-resolution techniques (IBSCA and NRA) to study the glass surface, he was able to give the most detailed description of the surface layers in case of lithium silicate glass. He described the equilibrium at the glass/solution boundary as a dynamic equilibrium not only in terms of thermodynamics, but also of electrochemical kinetics. For the first time in the literature of GEs, he has pointed to the electrochemical mechanism of formation of the GE potential as a consequence of charge division at the boundary (the dissociation mechanism). His activity in the field crowns the century with dignity.