Mixed-bed solid phase and its use in the isolation of nucleic acids

Mixed-bed solid phases are provided, with methods for using such solid phases to isolate target nucleic acids, such as plasmid DNA, chromosomal DNA, RNA, or nucleic acids generated by enzymatic amplification from contaminants, including proteins, lipids, cellular debris, or other nucleic acids. The mixed-bed solid phases of this invention are mixtures of at least two different solid phases, each of which has a capacity to bind to the target nucleic acid under different solution conditions, and the capacity to release the nucleic acid under similar elution conditions. By exchanging solution conditions according to the methods of this invention, one can remove contaminants from the target nucleic acid bound to the mixed-bed solid phase, then elute the target nucleic acid in an elution buffer.