Abstract: A process for separating a selected amino acid (enantiomer) from a mixture of different compounds including other amino acids is disclosed, in which process the mixture is contacted with a polymer material which is composed of cross-linked, amino-acid-based monomer units, said polymer material containing a molecular print of the selected amino acid. In the molecular print there is also bound a diastereomeric complex between the selected amino acid (enantiomer), a divalent metallic ion and the amino-acid-based monomer unit. Also the amino-acid-based monomer unit and a process for preparation thereof, as well as a polymer material composed of the amino-acid-based monomer unit and a process for the preparation thereof are disclosed.