ION EXCHANGE CHROMATOGRAPHY Xarrin Sindhu
Nov 19, 2014
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
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.
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