A sampling device for a substance detection instrument includes a membrane comprising a porous support having a coating thereon, the coating comprising a carborane polysiloxane or an arylene polysiloxane, the membrane having a front side configured to be placed in contact with a test sample and a back side; a sample line having an inlet proximate to the back side of the membrane and an outlet in fluid communication with a substance detector; and a source of carrier gas in fluid communication with the back side of the membrane and the sample line inlet.