A BRIEF REVIEW ON ION EXCHANGE CHROMATOGRAPHY

 

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ABOUT AUHTORS
Jaha Sultana Mohammed
Pelcat Formulation PVT ltd
sohnivya786@gmail.com

ABSTRACT:
Ion exchange chromatography is probably the most powerful and classic type of liquid chromatography. The popularity of ion exchange chromatography has been increased in recent years because this technique allows analysis of wide range of molecules in pharmaceutical, biotechnology, environmental, agricultural and other industries for water purification to separation of various antibiotics from fermentation broths which will enhance the yields and reduce the production time for industrial process. The main objective of this particular study is to develop some understanding for the process of ion exchange and helps to determine whether or not ion exchange will be useful for a particular application. This topic includes background, theory, instrumentation, application which covers both the production of the ion exchange substance, a resin and its operation depending on the condition of matrix during use.

REFERENCE ID: PHARMATUTOR-ART-2464

PharmaTutor (ISSN: 2347 - 7881)

Volume 5, Issue 2

Received On: 22/09/2016; Accepted On: 28/09/2016; Published On: 01/02/2017

How to cite this article: Mohammed JS; A brief review on Ion Exchange Chromatography; PharmaTutor; 2017; 5(2); 30-38

INTRODUCTION:
Chromatography literally means “colour writing”. Ion exchange chromatography involves the separation of ionizable molecules based on their total charge. This technique enables the separation of similar types of molecules that would be difficult to separate by other techniques because the charge carried by the molecule of interest can be readily manipulated by changing buffer pH. Columns used for ion exchange are characterized by the presence of the charged group covalently attached to the stationary phase. Anion exchanger contains bounded positive groups, where as cation exchanger contains bounded negative groups.

BACKGROUND:
The phenomenon of ion exchange was first reported by two British Agricultural Chemists and date back to 1850. After the work of Gans in 1913 natural and synthetic (soils, clays and Zeolites) inorganic cation exchangers were used for softening of hard water. Modern ion exchange resins were first used by Adams and Holms in 1935 in which large variety of synthetic resins have been developed [1]. This technique has been developing since 19th century which was firstly used for purification of drinking water.

DEFINITION:
Ion exchange chromatography can be defined as a reversible process in which ions of same sign are exchanged between solid and liquid, a highly insoluble body in contact with it. The soil is known as an ion exchanger and no substantial organic polymer has been used as ion exchanger [1, 2]. It is also known as cation-anion exchange chromatography.
Ion exchange chromatography, which is also known as adsorption chromatography, is a useful and popular method due to it’s:
1. High capacity,
2. High resolving power,
3. Mild separation conditions,
4.Versatility and wide speared applicability,
5.Tendency to concentrate the sample relatively low cost [3].

PROPERTIES OF ION EXCHANGE CHROMATOGRAPHY:
The most common properties of all ion exchangers which have been used in analysis are:
* It should be almost insoluble in water and organic solvents, like benzene, carbon tetrachloride, ether etc.
* It should be complex in nature and in fact they are polymeric.
* It should contain active or counter ions that will leads to exchange reversibility with other ions in a surrounding solution without any substantial change in the material [9-12].

ADVANTAGES:
* Detectability: Useful for the detection of many inorganic salts and also for the detection of organic ions with poor UV absorptivity likes alkyl amines or sulfonates.
* Preparative separations: Usually preferred because of the availability of volatile buffers. Volatile buffer 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 mixture of biological origin, in organic salts and some organometallics.
* Provides long life to resin [1, 2].
* Cheap maintenance
* Environmental friendly because it deals only with substance occurring in water.

THEORY:
The principle of separation is by reversible exchange of ions between the ions present in the solution and those present in the ion exchange resin. Ion exchange separations are mainly carried out in columns packed with an ion exchanger. There are two types of ion exchanger, namely
1. Cationic exchangers
2. Anionic exchangers

Cationic exchangers:
It possesses negatively charged groups and these will attract positively charged groups. These exchangers are also called acidic ion exchange materials since their negative charges result from the proteolysis of acidic groups

Anionic exchangers:
It has positively charged groups, which will attract negatively charged molecules. This exchanger is termed as basic ion exchange materials since their positive charges generally result from the association of protons with basic groups. Based upon the affinity of ions towards the matrix the ions like cation and anion are separated. The ions that have less affinity towards matrices will elute first and the ions that have more affinity towards matrices it will elute later [3-12].

The actual ion exchange mechanism is thought to be composed of five distinct steps:
1.  Diffusion of the ion to the exchanger surface. This occurs very quickly in homogeneous solutions.
2. Diffusion of the ion through the matrix to the exchanger site. This is dependent upon the degree of cross linkage of the exchanger and the concentration of the solution.
3. Exchange of ions at the exchange site occurs. This occur instantaneously in an equilibrium process:
 Resin - SO3H + Na+----------------->Resins - SO3Na + H+
 Resin - N(CH3)3OH  + Cl- ----------->Resin - N(CH3)3Cl  + OH-
4. Diffusion Of the exchanged ion through the exchanger to the surface
5. Selective desorption by the eluent and diffusion of the molecule into the external solution takes places [12-14].

ION EXCHANGERS:
Ion-exchange processes are used to separate and purify metals, including separating uranium from plutonium and other actinides, including thorium and lanthanum, neodymium, ytterbium, samarium, lutetium, from each other and the other lanthanides.
There are three classes of ion exchangers, these includes
1.  Resins
2.  Gels
3.  Inorganic exchangers

RESINS:
Resins are amorphous particles of organic materials which are composed of polystyrene and divinely benzene. Polystyrene contains sites for exchangeable functional groups. Divinely benzene acts as a cross linking agents and offers adequate strength i.e., mechanical stability. Ion exchange resins are used for separation of small molecules.

Classification of resins:
I.   According to their chemical nature, they can be classified as
1. Strong cation exchange resin: These types of resins are useful for the chromatographic separation of amino acids, rare earths and other substances that contains sulphonic acid groups as the ionisable groups [1-12].
2.  Weak cation exchange resin: These resins are based on polymers of methacrylic acid and possess carboxyl groups [1-12].
3.Strong anion exchange resin: These resins with positively charged quaternary ammonium groups attached to cross linked polystyrene frame work belong to this class. Trimethyl ammonium groups are used for this resin [1-12].
4.  Weak anion exchange resin: The tertiary amine resins and polyamine resins having a mixture of primary, secondary and tertiary amine groups on the polystyrene network are well known [1-12].

II.    According to the source, they are classified as
1.    Natural source: These are of two types
a.    Cation: E.g: Zeolytes, clay etc
b.    Anion: E.g: Dolomite
2.    Synthetic source: These are of two types
a.    Inorganic and
b.    Organic resins.
Of the above types, organic resins are the most widely used [14].

General requirements of resins:
It should be chemically stable.
It should be insoluble in most of the common solvents.
It should have high degree of exchange of ions.
If it swells then it should be denser than water molecule.
It must contain sufficient number of ion exchange groups.

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