Provided are impactors for detecting biologics having an adjustable separation distance between an impact surface and the intake aperture, including the exit of the intake aperture. The impactor has a sampling head having at least one intake aperture and an exit, an impactor base comprising an impact surface, wherein the impact surface opposibly faces the sampling head exit and is separated from the exit by a separation distance. The separation distance is continuously adjustable between a minimum separation distance and a maximum separation distance and can accommodate impact surfaces having different heights by positioning the impact surface, irrespective of height of the impact surface, at an optimal separation distance from the sample intake aperture, such as by a rotation-type mechanism with a change in distance indication provided to a user by a separation distance step indicator.