A New Type of Fe2O3-Based Silicone Composite pH Electrode and Potentiometric Applications

Abstract

A new type of Fe<inf>2</inf>O<inf>3</inf> based silicone composite pH electrode was investigated for using as a potentiometric pH sensor. Potentiometric performance characteristics of the prepared electrode were tested in steady-state conditions by using a computer-controlled potentiometric system. The electrode was constructed with a mixture of sulfated iron (III) oxide, graphite powder and silicone. The best potentiometric response was obtained with an electrode composition of 25% (w/w) sulfated iron (III) oxide, 35% (w/w) graphite powder and 40% (w/w) silicone. A linear response from pH 2 to 12 with a slope of 32.9±1.1 mV/pH; r = 0.9955 (at 25 °C) was observed. The electrode had a very short response time (<10 s) and good reproducibility. There were no significant changes in the slope of the pH-potential curve during the one year of service life. Selectivity coefficients of pH electrode against interfering ions (K+, Na+, Li+, NH+<inf>4</inf>, NO-<inf>3</inf>, SO2-<inf>4</inf>, CH<inf>3</inf>COO- and HCOO-), calculated by the "mixed solution method" for the H<inf>3</inf>O+ ion, were found comparable. pH values of various soft drinks, milk and medicine samples were measured with a pH electrode. The obtained potentiometric results for soft drinks, milk and medicine samples are in good agreement with a glass pH electrode, resulting in a 95% confidence level. © © 2015 American Scientific Publishers.