Cleaning Procedure for the Screen-Printed RuO2 pH Electrodes

Screen-printed RuO 2 pH electrodes are suitable for pH determination not only in water samples but also in different food matrixes, e.g., beverages, juices and milk. Nevertheless, the application of the screen-printed RuO 2 electrodes in milk is impossible without covering the electrodes with a protective Nafion membrane that prevents the contamination of the pH-sensitive area of the electrode with sample residues. However, not much attention has been paid to the cleaning procedure of Nafion-covered screen-printed RuO 2 electrodes (RuO 2 -Nf). In this paper, we show that cleaning the electrodes by soaking them in the solution of 5% pepsin in 0.1 M HCI allows restoring the electrode to its initial state for measuring pH in food samples.