It is a modified version of high-performance liquid chromatography (HPLC) and is based on the phenomenon of attraction between opposite charges. In other words, it’s based on the theory that opposites attract!

The method combines both chromatographic and ion equilibrium theories into one technique in order to separate ionic species. It is commonly used in biomolecule purification, and there are several specialized modes used in laboratories today. Scientists and researchers rely on ion chromatography for its usefulness at all stages and levels of purification, it’s concentrating and controllable capabilities, as well as its high selectivity, capacity, and recovery.

Furthermore, it is able to look at major anions such as fluoride, chloride, nitrate, nitrite, and sulfates, as well as major cations such as lithium, sodium, ammonium, potassium, calcium, and magnesium. However, this chromatography method must be performed in an environment that is one unit away from the isoelectric point (pl) of a protein.

The principle of ion exchange chromatography is as follows:

“A 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.”

The stationary phase is typically a polymeric resin. It’s selected so that it has a particular charge and attracts the sample molecules with the opposite charge. This phase is also termed as the ion exchanger. The ion exchanger can be two types, either a cation exchanger or an anion exchanger. Cation exchangers have a negative charge and attract positively charged cations, while anion exchangers are positively charged and attract negatively charged anions.

The mobile phase, or eluent, is a typically a solution—an inorganic salt dissolved in a suitable solvent—which introduces the ions that need to be separated into the system. Aqueous acid and base solutions, as well as organic, non-aqueous solutions can also be used as the mobile phase. The solution acts as the carrier portion of the mobile phase, and carries the analytes through the ion chromatograph.

There are a number of ion chromatography analyses performed in laboratories today, some of which include ammonia, cyanide, transition metals, and pharmaceuticals analysis. Yet, despite each method’s distinct uses, ion chromatography instrumentation is composed of several standard components and is similar to that of HPLC: a pumping system, chromatography columns, and a detecting system.