Immunoaffinity chromatography can be applied to the treatment of biological samples. It consists of the separation, extraction, or purification of a molecule (para nitro analine in this paper) from a mixture by a selective interaction with an antibody. The latter is produced by living organisms after their contact with an antigen (modified protein in this case). The production of specific antibodies highly depends on the purity of antigen. This paper describes and compares two methods of antigen purification: dialysis and gel permeation chromatography. This chromatographic method allows one to obtain a pure antigen faster than dialysis but with a slightly larger dilution of the samples. It is not a drawback for the procedure of the antibodies production.