The present invention relates to a separation matrix comprised of a support to the surfaces of which polymer chains have been coupled, wherein each polymer chain presents recurring proton-donating groups and at least the surface of the support is substantially hydrophilic. In the most advantageous embodiment, the support is porous cross-linked agarose, the polymers are poly(acrylic acid) and the proton-donating groups are carboxyl groups. The matrix is useful e.g. to remove PEG from pegylated and/or native compounds in a liquid. Accordingly, the invention also encompasses a method, such as a chromatographic method, wherein the separation matrix according to the invention is used, for example as a pre-treatment of a reaction mixture that comprises unreacted PEG, pegylated proteins and native proteins.