Potentiometric dissolved oxygen sensors with reference electrode integrated in thick film technology

New designed dissolved oxygen potentiometric sensors in thick film technology based in the use of RuO ₂ as active material and TiO ₂ or polyisoftalamide diphenylsulphone (PIDS) as membranes have been developed. TiO ₂-coated RuO ₂ electrodes showed a linear response as a function of the logarithm of the dissolved oxygen concentration in the 0.5-8 ppm range. The electrode displays a Nerstian slope of 59.4 mV/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 TiO ₂-coated RuO ₂ electrodes as a function of the proton concentration showed a relatively low e.m.f variation at neutral and basic pH indicating that the TiO ₂ coating appears to be a suitable layer capable of effectively isolate the RuO ₂ surface from ionic species from the solution. The reference electrode developed in thick-film technology presents a standard voltage of 0.025V vs ENH at 25 °C, with a drift of 10 mV/day and without interference.