A commercial pH-responsive glass (SiO2-25Li2O-7TiO2-5BaO-3mol%La2O3) was subjected to heat treatment in a vacuum furnace, and the pH response of the heat-treated specimen was compared with that of as-received glass. It was found that the heat-treated specimen, in which the content of so-called mobile H ions had been decreased, exhibited a much lower Nernst slope than the ideal value (59mV). It was concluded that the generation of pH selectivity originated from a H-ion concentration cell between the test solution and the glass electrode, and that an essential factor required for a glass specimen to exhibit a pH response was that the glass should contain mobile H ions.

Y.Abe, M.Maeda, N.Hayakawa, H.Umehara, M.Nogami: Materials Research Bulletin, 1997, 32[11], 1535-42