1 This removes co-precipitated salt and replaces the isopropanol with the more volatile ethanol, making the DNA easier to redissolve. 2  Centrifuge at 10,000–15,000 x g for 5–15 min at 4°C. 3  Repeat the washing and centrifugation steps once more. 4  Carefully decant the supernatant without disturbing the pellet.