The hydrogen-ion response of the glass electrode in aqueous and partially-aqueous solutions

Abstract

The existence of small errors, previously reported for hydrogen-ion responsive glass electrodes in standard and other buffer solutions of intermediate pH are confirmed. Such errors, apparent for all types of glass electrode tested above pH 2.5, are independent of the pH and total ionic strength of the solution, but are a function of the buffer composition and its molality. They increase with decreasing buffer concentration and are independent of the nature of added salt. For a particular glass electrode, the magnitude of the error is determined by the glass composition and its past use. Reports that improved time responses and smaller or insignificant errors are obtainable in partially and non-aqueous solutions for glass electrodes soaked in the test solution solvent medium, and preferably, with internal fillings of either a solution in the same solvent or mercury, were not substantiated. Results of a survey, in aqueous, methanol-water and N, N-dimethylformamide-water mixture solutions, for glass electrodes with alternative fillings and conditioning, show responses are modified for some solvent mixtures. More detailed study is necessary before the observations can be properly explained. Studies of the hydrogen-ion functions and durabilities for soda-lime and lithia-lime glasses reveal a meaningful correlation between pH response properties and the ratio of alkali: lime leached extracts. Compositions with good pH response functions have similar oxide ratios for the glass and the extract.