INDISPENSABILITY OF THE PRESENCE OF MOBILE HYDROGEN-IONS IN GLASS FORITS PH RESPONSE

A commercially available pi-I-responsive glass specimen with the molar composition of 25Li(2)O-5BaO-3La(2)O(3)-7Ti0(2)-60SiO(2) was subjecte d to heat treatment in a vacuum furnace and the pH response of the hea t-treated glass specimen was compared with that of the as-received gla ss. It was found that the heat-treated glass specimen in which the con tent of ''mobile'' hydrogen ions was decreased showed a much lower Ner nstian slope than the ideal value (59 mV). From these findings, we con clude that the generation of the pH selectivity originates from a hydr ogen-ion concentration cell between a solution of a given pH and a gla ss electrode material and that an essential factor for a glass specime n to exhibit the pH response is that the glass should contain ''mobile '' hydrogen ions. (C) 1997 Elsevier Science Ltd.