New potentiomentric dissolved oxygen sensors in thick film technology

New designed dissolved oxygen potentiometric sensors in thick film technology based in the use of RuO2 as active material and TiO2 or polyisoftalamide diphenylsulphone (PIDS) as membranes have been developed. TiO2-coated RuO2 electrodes showed a linear response as a function of the logarithm of the dissolved oxygen concentration in the 0.5–8 ppm range (log[O2], −4.82 to −3.60; concentration of O2 in mol dm−3). The electrode displays a Nernstian slope of 59.4 mV per decade at 25 °C. The value of this slope suggests the presence of a reaction involving one electron per oxygen molecule that was tentatively attributed to the formation of super-oxide ions at the electrode surface. Studies on TiO2-coated RuO2 electrodes as a function of the proton concentration showed a relatively low emf variation at neutral and basic pH indicating that the TiO2 coating appears to be a suitable layer capable of effectively isolate the RuO2 surface from ionic species from the solution. RuO2 surfaces were also covered with a polymeric membrane (polyisoftalamide diphenylsulphone). For the PIDS-coated RuO2 electrode a linear response as a function of the logarithm of the dissolved oxygen concentration in the 0.8–8 ppm range (log[O2], −4.60 to −3.60) was observed with a slope of 37.4 mV per decade at 25 °C. This electrode does not show any significant emf variation as a function of the pH at a fixed concentration of oxygen. As a drawback, the PIDS polymeric membrane showed a limited adherence on the electrode surface.