Installing a catalytic filter upstream can mitigate the cross-sensitivity of a gas sensor by converting (e.g., oxidizing , using O 2 in air) interferents into species that interact more weakly with its recognition element -thereby enhancing the selectivity of the sensing device for the analyte over the interferent. A catalytic filter can be : (i) a tubular reactor packed with catalyst particles or (ii) a porous, catalytic film overlaying the recognition element . Several catalytic filters have been experimentally demonstrated for diverse gas sensing tasks involving interferents . The design parameters of the catalytic filter, incl. the catalyst, operating temperature, and residence time of the gas in it, must be tuned to optimize the performance of the sensor. Particularly, an imperfectly reactant-selective catalyst in the filter will degrade the analyte as well as the interferent-especially in cases where the analyte and interferent are chemically similar. Consequently, in these cases, we hypothesize that an optimal e.g. residence time (for the gas stream containing analytes and interferents) exists. A short residence time allows too much interferent to reach the sensor and corrupt its response, while a long residence time allows too much of the analyte to be converted, diminishing the signal-to-noise ratio.