The detection of gaseous pollutants such as Benzene, Toluene, Ethylbenzene and Xylene (BTEX) under real conditions requires working in a humid environment. It is well known that the humidity reduces the performances of gas sensors, particularly in terms of sensitivity. Ionic liquids (ILs) are a new class of solvent with attractive properties for the extraction of volatile organic compounds (VOCs) or gases. Moreover, the ILs are particularly interesting because of their recycling ability and without atmospheric pollution. Using a filter based on a mixed ionic liquid ([Bmim][Br]-[Bmim][PF6]), low concentrations of BTEX are detected with a tungsten trioxide (WO3) thin film (50 nm) deposited by reactive RF magnetron sputtering on a transducer developed in our laboratory. With this filter upstream, we are able to detect 500 ppb of BTEX gases without a sensor sensitivity decrease with 50 % relative humidity.