The device comprises an extractor (53) having an outlet (71) at which a gas stream is sampled. The gas stream contains at least one hydrocarbon to be analyzed and at least one interfering compound. A transport line (54), is connected to the outlet (71) of the extractor (53) to transport the gas stream to an analyzer (55A) comprising a detector being able to measure at least one of the hydrocarbons to be analyzed contained in this gas stream. The device comprises a chemical reactor (141) located between the extractor (53) and the detector. At least a portion of the extracted gases is transported through the chemical reactor (141) where a selective catalytic reaction of at least one interfering compound is carried out without any substantial reaction of at least one of the hydrocarbons to be analyzed.