NOVELTY - The method involves passing a gas sample (18) through a catalyst arrangement (12) before supplying the gas sample to a sensor device (14), where the gas disturbing detection of the interesting gas is removed from the catalyst arrangement. Gases (18a, 18b) in the gas sample are converted in the catalyst arrangement into gases (20a, 20b) e.g. carbon monoxide, hydrogen sulfide and methane, which are easily detectable by the sensor device, where nickel, copper, chromium, zinc oxide, platinum, gold, iron or cobalt are used as catalyst in the catalyst arrangement.    USE - Method for increasing sensitivity and selectivity of a sensor device e.g. gas sensor such as metallic oxide sensor and physical gas sensor, utilized for detection of gases e.g. carbon monoxide, hydrogen sulfide and methane, in a gas sample e.g. single gas, inorganic and/or organic gaseous mixture and/or aerosol (all claimed), for determination of room air quality or early fire recognition.    ADVANTAGE - The method allows supplying the gas sample through the catalyst arrangement before supplying to the sensor device, so that the gas disturbing detection of the interesting gas is removed from the catalyst arrangement, thus preventing influence of the disturbing gas on the detection of the interesting gas, hence enhancing detection of the gas by the sensor device. The method allows the sensor device to detect gases of all substance classes such as alkane, alcohol, aldehyde, ketone, ester and aromatics. The catalyst arrangement is detachably arranged in the sensor arrangement, so that only the catalyst arrangement is replaced, when the catalyst arrangement is poisoned, thus preventing the need for replacing the entire sensor arrangement.    DETAILED DESCRIPTION - The catalyst arrangement is formed as a full catalyst in form of a gas-permeable lattice, a net or porous solid, a sponge or a membrane. An INDEPENDENT CLAIM is also included for a sensor arrangement for detection of gases in a gas sample.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view of a sensor arrangement.    Catalyst arrangement (12)    Sensor device (14)    Gas sample (18)    Gases (18a, 18b)    Easily detectable gases (20a, 20b)