G-Biosciences DNA Size Selection & PCR Cleanup Magnetic beads are suitable for PCR clean-up and DNA fragment size selection from 150 bp to 1000 bp and even larger. They remove excess nucleotides, salts, enzymes, and other impurities with a simple washing process to obtain purified fragments, which can be directly used in downstream applications such as sequencing, hybridization, and enzyme digestion. DNA size selection depends on optimizing magnetic beads, target DNA ratio, and salt concentrations.