Cleaning Procedure for the Screen-Printed RuO2 pH Electrodes

Screen-printed RuO2 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 RuO2 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 RuO2 electrodes (RuO2-Nf). In this paper, we show that cleaning the electrodes by soaking them in the solution of 5% pepsin in 0.1 M HCl allows restoring the electrode to its initial state for measuring pH in food samples.