This invention relates generally to modified porous solid supports and processes for the preparation and use of same. In particular, passivated porous supports are disclosed which are characterized by a reversible high sorptive capacity substantially unaccompanied by non-specific adsorption of or interaction with biomolecules. Passivation is achieved by use of a passivation mixture comprising a main monomer, a passivating agent comprising polyethyleneimine, and a crosslinking agent, which mixture upon polymerization results in the substantial elimination of the undesirable non-specific interaction with biomolecules.