Why are Salts Removed before Ion-Exchange Chromatography?
Think about what the ion-exchange material does, and the mechanism of separation by this method. The ions of interest interact with the ion exchange sites to a different degree than do the other ions or other species in the solution, thus you get separation.  What if your solution is loaded down with ammonium sulfate?  The ion exchange resins have a limited capacity to accommodate ions and all of the sites would be swamped in ammonium ions and all of the much lower concentration ions of interest thus would not be able to be separated.