Adsorption Chromatography

What is Adsorption Chromatography?

Adsorption chromatography is the oldest type of chromatography technique. It makes use of a mobile phase which is either in liquid or gaseous form. The mobile phase is adsorbed onto the surface of a stationary solid phase.

Table of Contents

• Adsorption Chromatography Principle
• Adsorption Chromatography Diagram
• Adsorption Chromatography Procedure
• Adsorption Chromatography Experiment (TLC)
• Adsorption Chromatography Applications
• Types Of Adsorption Chromatography
• FAQs

Adsorption Chromatography Principle

Adsorption Chromatography involves the analytical separation of a chemical mixture based on the interaction of the adsorbate with the adsorbent. The mixture of gas or liquid gets separated when it passes over the adsorbent bed that adsorbs different compounds at different rates.

Adsorbent – A substance which is generally porous in nature with a high surface area to adsorb substances on its surface by intermolecular forces is called adsorbent. Some commonly used adsorbents are Silica gel H, silica gel G, silica gel N, silica gel S, hydrated gel silica, cellulose microcrystalline, alumina, modified silica gel, etc.

Adsorption Chromatography Diagram

Adsorption Chromatography Procedure

Before starting with the adsorption chromatography Experiment let us understand the two types of phases and the types of forces involved during the mixture separation process.

• Stationary phase – Adsorbent is the stationary phase in adsorption chromatography. The forces involved help to remove solutes from the adsorbent so that they can move with the mobile phase.
• Mobile phase – Either a liquid or a gas is used as a mobile phase in adsorption chromatography. Forces involved help to remove solutes from the adsorbent so that they can move with the mobile phase. When a liquid is used as a mobile phase it is called LSC (Liquid-Solid Chromatography). When a gas is used as a mobile phase it is called GSC (Gas-Solid Chromatography).

Apparatus –

Chromatography jar – The glass jar has a lid. It helps to maintain a proper environment during separation.

Thin-layer chromatography plate – Borosilicate glass plate with size 20×20 cm, 20×5 cm, 20×10.

Capillary tube – Sample mixture is applied to TLC with the help of this tube.

Mobile phase – Liquid or gas

Stationary phase – Adsorbents

Adsorption Chromatography Experiment (TLC)

• Take a clean and dry chromatographic jar.
• To make sure that the environment in the jar is saturated with solvent vapours, a paper soaked in the mobile phase is applied to the walls.
• Add the mobile phase to the jar and close it.
• Maintain equilibrium
• Mark the baseline on the adsorbent.
• Apply sample to TLC plate with the help of a capillary tube and allow it to dry.
• Put the plates in the jar and close it.
• Wait until the solvent moves from the baseline.
• Take out the TLC plate and dry it.

Adsorption Chromatography Applications

• Adsorption chromatography is used for the separation of amino acids.
• It is used in the isolation of antibiotics.
• It is used in the identification of carbohydrates.
• It is used to separate and identify fats and fatty acids.
• It is used to isolate and determine peptides and proteins.

Types of Adsorption Chromatography:

1. Thin Layer Chromatography – It is a chromatography technique where the mobile phase moves over an adsorbent. The adsorbent is a thin layer which is applied to a solid support for the separation of components. The separation takes place through differential migration which occurs when the solvent moves along the powder spread on the glass plates.
2. Paper chromatography – It is a technique that uses paper sheets or strips as the adsorbent being the stationary phase through which a solution is made to pass is called paper chromatography. The solid surface of the paper is the stationary phase and the liquid phase is the mobile phase.
3. Column chromatography – the technique in which the solutes of a solution are entitled to travel down a column where the individual components are adsorbed by the stationary phase. Based on the affinity towards adsorbent the components take positions on the column. The most strongly adsorbed component is seen at the top of the column.
4. Gas-Solid chromatography – The principle of separation in GSC is adsorption. It is used for solutes which have less solubility in the stationary phase. This type of chromatography technique has a very limited number of stationary phases available and therefore GSC is not used widely.

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Frequently Asked Questions – FAQs

Q1

How does adsorption chromatography work?

Adsorption Chromatography involves the separation of a chemical mixture based on the interaction of the adsorbate with the adsorbent. In this process, the mixture of gas or liquid gets separated on the adsorbent bed that adsorbs different compounds at different rates.

Q2

Is TLC partition or adsorption chromatography?

TLC is an adsorption chromatography technique. In this process a sheet of glass, plastic, or aluminium foil, which is coated with silica gel, aluminium oxide or cellulose acts as a stationary phase and a single solvent or a mixture of solvent like ethanol and chloroform act as mobile phase.

Q3

What are the 4 types of chromatography?

The 4 types of chromatography are Thin Layer Chromatography, Paper chromatography, Column chromatography and Gas-Solid chromatography.

Q4

What is Rf value?

The retention factor of a particular material is the ratio of the distance the spot moved above the origin to the distance the solvent front moved above the origin. The formula is Rf = distance spot moved /distance solvent moved

Q5

Can Rf value be greater than 1?

Rf values are always less than 1. From the definition “Rf = distance spot moved /distance solvent moved” . If the Rf value of 1 or too close it means that the spot and the solvent front travel close together and is therefore unreliable. This happens when the eluting solvent is too polar for the sample.