Ion exchange chromatography (or ion chromatography) is a process in chromatography that separates ions and polar molecules based on their attraction to the ion exchanger. It works on almost any kind of charged molecule—including large proteins, small nucleotides, and amino acids. The two types of ion chromatography are: "anion-exchange" and "cation-exchange" chromatography. They are used in protein purification, water analysis, and quality control.