Ion-exchange chromatography (IEC) is part of ion chromatography which is an important analytical technique for the separation and determination of ionic compounds, together with ion-partition/interaction and ion-exclusion chromatography. It is based on  ionic interactions between ionic and polar analytes, ions present in the eluent and ionic functional groups fixed to the chromatographic support. IEX chromatography is used in the separation of charged biomolecules. The crude sample containing charged molecules is used as the liquid phase. When it passes through the chromatographic column, molecules bind to oppositely charged sites in the stationary phase. The molecules separated on the basis of their charge are eluted using a solution of varying ionic strength. By passing such a solution through the column, highly selective separation of molecules according to their different charges takes place.