Ion Exchange Chromatography: Properties of Ion Exchangers & Factor Affecting Ion-Exchange MCQ Part 2

Ion Exchange Chromatography- Part 2 

Properties of Ion exchangers :-

The common property of all ion exchanger are as follows :-

1. They are insoluble in water and organic solvent like carbon tetrachloride, benzene, chloroform etc.
2. They are complex in nature. Usually polymeric in nature.
3. They possess active ions or counter ion that are easily exchange with other ions.

Cation Exchangers :-

It is a high molecular weight and cross- linked polymer having sulphonic, carboxylic, phenolic group etc.

In cationic exchange hydrogen ion are mobile and exchangeable with other cation and the anion remain attracted to resin

When a salt solution is passed through cation exchanger, the Hydrogen ions enter the solution and the cations of the salt get attached to resin.

Resin-H + M → Resin-M + H (Solution)

Strong cation Exchange resins consists of SO3H¯ group and weak cation exchange resin consists of group like COOH¯,OH¯,SH¯ etc.

Anion exchangers :-

Anion exchangers are usually resins consists of amine or Quaternary ammonium group as integral part and equal amount of Ce¯, So4¯,OH¯ ions which are mobile and Exchange able.

Resin-OH¯ + A¯ → Resin- A‾ + OH¯

Strong anion exchange resins consists of group such as NR2, NR3 etc. And weak anion exchange resins consists of NHR,NH2 group etc.

Mechanisms of ion-exchange process :-

1. The ion diffuses to the exchanger surface. This occur very quickly in homogenous solution.
2. The ion diffuses from the matrix structure to the exchange site which is based on the degree of cross linkage of resin and the concentration of Solution This step is considered to be the rate determining step of ion Exchange process.
3. The exchange of ions take place at the exchange site which occur instantaneous till equilibrium is attained.
4. The exchanged ion diffused through the exchanger to the surface.
5. The molecule are separated by altering the pH or ionic concentration or by affinity elusion in which the ion with greater affinity for the exchanger their the bound molecule is employed

Factor Affecting Ion – Exchange :-

1. Nature of Exchange resins :-

The cross linking and swelling property of Exchange play an important role in Exchange of ions. When more cross linking agent is present the resins become rigid and swell less and when less cross linking agent is present, the resin swelling the less separation of ions. Different sizes become difficult as they can’t pass through out the pore and if the swelling is more the separation is not effective because of the wide range of pore

2. Nature of the exchanger ions :-

A. The exchange increase with increase in valency at low concentration and ordinary temperature

Na<Ca<Al

B. For similar charged ion exchange increase with decrease in the size of hydrated ion.

Li<H<Na<NH4

3. The greater polarizable ion has great exchange capacity

I¯<Br¯<Cl¯<F¯

4. Polyvalent anion are generally absorbed preferentially in dilute solution.

5. If the resin has higher positive charge and solution has lower positive charge, Exchange is favoured at higher concentration and vice versa.

MCQ

1. Which is not a property of ion Exchanger ?

A.They are complex in nature. Usually polymeric in nature.

B.They are insoluble in water and organic solvent like carbon tetrachloride, benzene, chloroform etc.

C.They possess active ions or counter ion that are easily exchange with other ions.

D. It is soluble in water.

2. Strong cation exchanger have functional group is ?

A. SO3H¯

B. COOH

C. OH

D. H

3. Which is example of stronger anion exchanger ?

A.NR2

B. NH

C. NH3

D. NO

4. Which is rate determining step in ion exchange process ?

A.The ion diffuses from the matrix structure to the exchange site which is based on the degree of cross linkage of resin and the concentration of Solution.

B. The ion diffuses from the matrix structure to the exchange site which is based on the degree of cross linkage of resin and the concentration of Solution

C. The exchange of ions take place at the exchange site which occur instantaneous till equilibrium is attained.

D.The exchanged ion diffused through the exchanger to the surface.

5. If the swelling is increases

A. It is easy to separation

B. It is difficult to separation

C. A and B

D. None of the above

6. If the polarizable ion is increases the rate of ion Exchange will be increased. Which of the following sequence is true according to the above statement ?

A. Na<Ca<Al

B. Li<H<Na<NH4

C. I¯<Br¯<Cl¯<F¯

D. I¯>Br¯>Cl¯>F¯

7.For similar charged ion exchange increase with decrease in the size of hydrated ion which  sequence is true according to above sentence?

A. Na<Ca<Al

B. Li<H<Na<NH4

C. I¯<Br¯<Cl¯<F¯

D. I¯>Br¯>Cl¯>F¯

Answer key

1. D

2. A

3. A

4. A

5. B

6. C

7. B

Reference :-

TEXT BOOK OF PHARMACEUTICAL ANALYSIS THIRD EDITION OF DR. RAVI SANKAR (16. 1TO16.10)