Effect of glass former (B2O3, SiO2, GeO2 and P2O5) addition to Fe2O3-Bi2O3 glass on pH responsivity

Abstract

The effect of glass former (constituent capable to vitrify by itself such as B2O3, SiO2, GeO2 and P2O5) addition to Fe2O3-Bi2O3 (FeBi) glass on pH responsivity (pH sensitivity and pH response time) was investigated in order to develop novel pH responsive, hydrophobic glasses. Additionally, the effect of glass composition on pH sensitivity of Fe2O3-Bi2O3 glasses was investigated in order to develop contaminant-free reference electrodes with very low pH sensitivity. A small amount of B2O3 and SiO2 drastically increased the pH sensitivity. The addition of glass formers of 20 mol% provided high pH sensitivity (>90%) in any of the glass formers. Although all glass formers increased their contact angle with water for Fe2O3-Bi2O3 glass, the addition of GeO2 was most effective. Most of the Fe2O3-Bi2O3-GeO2 (FeBiGe) glasses with 20–30mol% GeO2, which serve as a working electrode, had compatibility between high pH sensitivity and a high contact angle with water (100°). However, certain Fe2O3-Bi2O3 glasses with approximately 20 mol% Fe2O3 showed low pH sensitivity (<10%). These FeBi glasses are considered to serve as contaminant-free reference electrodes, whereas KCl aqueous solution, as a contaminant, gradually leaks in commercial reference electrodes (Ag/AgCl immersed in KCl aqueous solution). Since the novel pH complex glass electrodes, consisting of a FeBiGe working electrode and a FeBi reference electrode, resist fouling of itself and serve as contaminant-free glass electrodes, these electrodes are expected to be highly useful in biological systems and drug development.