Separation of Amino Acids

In ion-exchange chromatography, a solution containing a mixture of compounds is passed through a column packed with a resin containing covalently attached anionic and/or cationic functional groups. One use of ion-exchange chromatography is the separation of compounds based on differences in charge. For example, an anionic ion-exchange resin separates cations, which bind to the resin, from anions and neutral compounds, which pass through the column without binding to the resin. Suppose you need to separate the amino acids lysine and proline using ion-exchange chromatography.  To what pH should you adjust the amino acid solution so that the separation is possible? Briefly defend you choice and indicate which amino acid will elute from the column and which will remain on the column.