Ion exchange chromatography is an unusual type of column chromatography.
Chromatography is the process of the separation of molecules from a mixture.
This separation is done based on the differences in the adsorption coefficient or partition coefficient of the sample with the stationary phase.
Whereas in ion exchange chromatography segregation of molecules occurs based on ion displacement theory.
This can be seen by the example below
When Magnesium is allowed to react with hydrochloric acid, it forms a salt of Magnesium Chloride and Hydrogen gas.
Mg + 2HCl —————————> MgCl + H2
As seen in the above reaction, more reactive ion Mg replaces less reactive ion H to form MgCl.
Ion Exchange chromatography Principle
The charged molecules in the sample are separated by the electrostatic forces of attraction when passed through an ionic resin at particular pH and temperature.
The separation occurs by reversible exchange of ions between the ions present in the solution and those present in the ion exchange resin.
The process of separation of molecules from the mixture is dependent on the type of ion exchange resin used.
Ionic resins are of two types as
- Cation exchange resin
- Anion exchange resin.
Cation exchange resins are employed to retain cations in the column. And anion exchange resins are used to keep anions into the column from the sample.
Thus the process of separation would be like
Resin-H+ +M+ (in solution) ————> Resin-M+ + H+ (in eluting solution).
Resin-OH- +A- (in solution) ————> Resin-A- + OH-(in eluting solution).
As the desired ionic molecules are stuck in the resin, the column is allowed to exhaust (flow) till all the other ions are flushed out.
Then the desired ions stuck in the resin are allowed to flow out by passing a more reactive mobile phase through the column.
If cations (+) are present in the column, a strong base is moved into the column and vice versa.
Many drugs, enzymes, proteins and other pharmaceutical products are either acidic or basic in nature.
Hence this method can be used to separate and purify these charged compounds.
Applications of ion exchange chromatography.
Ion exchange chromatography is prominently used as preparatory chromatography to isolate the desired compound from the mixture. Hence the applications are meant to obtain pure compounds.
a) For deionization and softening of water.
b) Purification of a solution to keep them ion free.
c) In biochemistry for separation of drugs and metabolites from blood, urine, etc.
d) Used for separation of organic compound mixtures of proteins, carbohydrates, nucleotides, etc.
e) For purification of enzymes after extracting from the tissues.
Also see Gel Permeation Chromatography.