ION EXCHANGE CHROMATOGRAPHY

Xarrin Sindhu

Anion exchangers contain bound positive groups, where as cation exchangers contain bound negative groups

Columns used for ion exchange are characterized by the presence of charged groups covalently attached to the stationary phase

Ion-exchange chromatography is a process that allows the separation of ions and polar molecules based on their charge

Theoretical background

Ion exchange chromatography (Classification of resins)

Cationic exchangers and Anionic exchangers

Cationic exchangers are useful for separation of cations such as protonated bases and anion exchange columns are used for anions or acidic samples

Principle

If the stationary phase is represented by R− or R+and the sample by X+ and X−, retention in IEC can be represented as

X+ + R−K+ X+R− + K+ (cation exchange)

X- + R+Cl- X-R+ + Cl- (anion exchange)

Technique

A sample is introduced, either manually or with an autosampler, into a sample loop of known volume.

A buffered aqueous solution known as the mobile phase carries the sample from the loop onto a column that contains some form of stationary phase material. This is typically a resin or gel matrix consisting of agarose or cellulose beads with covalently bonded charged functional groups.

Cont’dThe target analytes (anions or cations) are retained on the stationary phase

Ion exchangers

There are three classes of ion exchangers , these include

1. Resins

2. Gels

3. Inorganic exchangers

Selectivity for ion exchange

• In general , ion exchangers favour the binding of ions of

• Higher charge

• Decreased hydrated radius

• Increased polarizability

• Ion exchange resins are used for the separation of small molecules.

• Ion exchange gels are used for the separation of large molecules like protiens ,nucleic acids.

• Separations involving harsh chemical conditions(high temperature , high radiation levels, strongly basic solutions or powerful oxidizing agents) employ inorganic ion exchangers

Advantages• Detectability: useful for the detection of many in-organic

salts and organic ions with poor uv absorptivity like alkyl amines or sulfonates.

• Preparative separations: usually preferred because of the availability of volatile buffers . volatile buffers makes the removal of mobile phase easier.

• Useful to resolve very complex samples, i.e in the case of multi step separation

• Useful for separation of mixtures of biological origin, in organic salts and some organo- metallics

Applications

• Conversion from one salt to other e.g we can prepare tetra propyl ammonium hydroxide from a tetra propyl salt of some other anion.

• household (laundry detergents and water filters) to produce soft water

• Ion exchange is used to prepare de-ionized water• separate and purify metals• Dealkalization• analysis and purification of immunoglobulins• Separation of inorganic ions