The present invention provides a substrate for purifying a biological liquid comprising a solid phase onto which molecules of at least one oligosaccharide that is capable of binding to one or more antibodies are grafted by covalent bonding, said solid phase carrying free aldehyde functions —CHO, a method of producing such a substrate, the use of such a substrate to stabilize the antibody/oligosaccharide bond, as well as a method of purifying a biological liquid in which the biological liquid is brought into contact with at least one substrate of the invention, in a manner such as to obtain the capture of antibodies present in said biological liquid by binding with at least certain of the molecules of oligosaccharide(s) grafted onto the solid phase.