The invention discloses a separation matrix with a porous solid support and a plurality of polyvinylpyrrolidone (PVP) polymer chains covalently attached to the solid support. The polyvinylpyrrolidone polymer chains are either vinylpyrrolidone homopolymer chains or copolymer chains which comprise at least 70 mol % vinylpyrrolidone monomer residues and less than 2 mol % negatively charged monomer residues.