Influence of temperature on the performance of Nafion coated RuO2 based pH electrodes

At present, ruthenium oxide (RuO2) based solid-state electrodes are investigated as an alternative to conventional glass electrode due to their low cost, chemical and physical durability, good sensitivity and fast response. Coverage of the solid-state electrodes with a protective membrane can improve the overall performance of the electrode and allow measurement in complex media, such as blood, food, biologically active environment. One of the well-known protective membranes for electrodes is Nafion. However, little is known about the performance of Nafion-covered electrodes used in heated samples. Here we present the investigation of the behaviour of ruthenium oxide (RuO2) based pH electrodes modified with Nafion protective membrane (RuO2-Nafion) at an elevated temperature of 80°C. RuO2 electrodes were fabricated by screen printing technique. We compare the performance of the RuO2-Nafion electrodes was compared to that of unmodified RuO2 electrodes. Both unmodified RuO2 electrodes and RuO2-Nafion electrodes perform well at room temperature, showing sensitivity close to the theoretical value (58.4 and 62.4 mV/pH respectively), the fast response time (14 and 42 s respectively) and low drift rate (0.5 and 0.4 mV/h respectively). The sensitivity of the Nafion- covered electrodes was found to be higher at elevated temperature as well: 37.2 mV/pH compared to 33.4 mV/pH for unmodified electrodes. Furthermore, RuO2-Nafion electrodes showed a lower drift rate at elevated temperature (9.6 mV/h) compared to that of modified electrodes (34.8 mV/h).