Magnetic separation is now deemed a simple and efficient method used in the purification of nucleic acids. It is a modification of solid-phase extraction. The beads have a negative surface charge and selectively bind to proteins, such as DNA. The binding process may sometimes be assisted by a magnet being applied to the side of the tube as this aggregates the particles near the wall. The remainder of the sample, consisting of cellular debris and unwanted material, can then be poured away. The nucleic acids are removed from the magnetic particles with a buffer and any remaining contaminants are washed away.