An apparatus for purifying nucleic acids by negative chromatography is disclosed, which comprises a hollow body with an opening, respectively, at the top and at the bottom end, said hollow body containing a stationary solid phase, characterized in that the stationary phase contains at least 2 different chromatography resins, such as size e.g. exclusion gel filtration materials (SEC materials), as well as a method for purifying nucleic acids and the use of the apparatus.