The invention includes a method for separating polynucleotides, such as DNA, RNA and PNA, from a solution containing polynucleotides by reversibly and non-specifically binding the polynucleotides to a solid surface having a functional amide group-coated surface. The materials containing a solid surface can be in the form of microparticles, fibers, beads, membranes, test tubes, pipette tips or microwells and can further comprise a magnetic core portion. The pH, salt and concentration of crowding reagent, such as polyethylene glycol or alcohol, of the solution is adjusted to levels which result in nucleic acid binding to the solid surface. The magnetic microparticles with bound polynucleotides are separated from the solution under mild alkaline conditions and the nucleic acids are eluted from the magnetic microparticles. Solutions having different nucleic acid concentrations can be normalized by restricting the availability of the solid phase surface.