Alkali-free Magnesium Phosphate Glasses as Nitrate-ion-selective Materials for Solid-state Electrochemical Sensors

Abstract

Abstract Ion-selective electrochemical sensors which respond to nitrate-ion activities have been developed. The sensor material consists of alkali-free magnesium phosphate glasses containing CuO, Al2O3, and SiO2. The response characteristics have been observed strongly on the glass composition. Studies of the selectivity coefficient and the electrode function of nitrate-ion activities have shown that the most suitable glass composition is 10CuO : 55P2O5 : 15MgO : 10Al2O3 : 10SiO2. The potential response is linear over the nitrate-ion activities of (10−1–10−5) mol/dm3, and it has a sub-Nernstian response of about 54 mV/decade change at 20 °C. The order of the selectivity is NO3−>ClO4−>I−>NO2−>Cl−>SO32−>>SO42−. Therefore, its use to determine the nitrate-ion activities in a solution containing perchlorate ions is suggested. The physical and chemical properties, such as the glass transition temperature, the softening temperature, the thermal expansion, the membrane resistance, and the chemical durability, were measured and compared with those of other glasses.