The supernatant containing the DNA is then exposed to silica in a solution with high ionic strength.
The highest DNA adsorption efficiencies occur in the presence of buffer solution with a pH at or below the pKa of the surface silanol groups.
The mechanism behind DNA adsorption onto silica is not fully understood; one possible explanation involves reduction of the silica surface's negative charge due to the high ionic strength of the buffer.
These conditions lead to an energetically favorable situation for DNA to adsorb to the silica surface.
[citation needed] A further explanation of how DNA binds to silica is based on the action of guanidinium chloride (GuHCl), which acts as a chaotrope.