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In the present investigation, LaCoO3 is used as an active filter for elimination of the sensor sensitivity to carbon monoxide and ethanol. A sol-gel procedure was used for the preparation of SnO2 fine powder, which was impregnated with hexachloroplatinic acid to obtain 1.0 wt% Pt on SnO2. The LaCoO3 perovskite fine powder was prepared by citrate method, using nitrate precursors of La and Co, to act as active filter. The LaCoO3 perovskite caused the sensitivity of the sensor to CO and ethanol declined significantly. It seems that the perovskite oxidizes CO and ethanol at temperatures lower than 250°C whereas methane is not affected at temperature as high as 450°C. This way the perovskite filter eliminates the sensor sensitivity to CO and ethanol, making the sensors highly selective to methane in presence of CO and ethanol in air.