Paper chromatography: Introduction, Methodology & Development techniques

Introduction:

• Paper chromatography is a technique used to separate mixtures of substances into their individual components, using paper as the stationary phase.

Paper Chromatography

• It's a form of partition chromatography where separation is based on differences in partitioning between the mobile phase (solvent) and stationary phase (paper).
  

Methodology:

Here's the diagram illustrating the "Methodology of Paper Chromatography"

The methodology of paper chromatography is intricate and can be broken down into several stages:

1. Paper Selection:

• Chromatographic paper, often made of cellulose, is selected based on its properties.

• The paper acts as the stationary phase.

2. Sample Preparation:

• The sample is usually dissolved in a suitable solvent to ensure it is in a liquid state for easy spotting onto the paper.

3. Spotting the Sample:

• Using a capillary tube or a micro-pipette, a small spot of the sample is applied near the bottom edge of the paper. It's crucial to make the spot as small and concentrated as possible.

• The position where the spot is applied is marked and is known as the origin.

4. Choice of Solvent (Mobile Phase):

• The solvent or solvent mixture, known as the developing solution, is carefully chosen based on the nature of the sample and the type of separation desired.
  

5. Chamber Saturation:

• The developing chamber (typically a glass container) is saturated with vapor of the developing solution to ensure a consistent atmosphere, which improves reproducibility.

6. Development:

• The paper, with the sample spotted onto it, is placed in the developing chamber in such a way that the solvent is below the level of the applied spot.

• As the solvent rises through the paper by capillary action, it flows over the sample spot, and the components of the sample begin to move up the paper at different rates based on their respective affinities for the mobile and stationary phases.

7. Termination:

• Once the solvent has traveled a desired distance, the paper is removed from the chamber.

• The solvent front (the maximum distance traveled by the solvent) is marked immediately.
  

8. Visualization:

• Many compounds may be colorless and thus not directly visible on the paper after development.

• Depending on the compounds, several methods can be used:

  1. UV Light: Compounds that fluoresce can be visualized under UV light.

  2. Staining: The paper can be immersed in or sprayed with a chemical that reacts with the sample compounds to produce colored spots.

  3. Iodine Vapors: Useful for visualizing some types of organic compounds.

9. Analysis:

• The separation can be analyzed by measuring the distance each compound traveled from the origin and comparing it to the distance traveled by the solvent. This is often expressed as the Rf value (Retention factor).

Development Techniques:

Here's the diagram illustrating the "Development Techniques in Paper Chromatography

1. Ascending Chromatography:

• The most common technique where the solvent moves up the paper.

2. Descending Chromatography:

• The paper's top edge is immersed in the solvent, and the solvent moves downward.

3. Radial or Circular Chromatography:

• The sample is spotted in the center of a circular paper, and the solvent moves outward in a radial direction.

4. Two-dimensional Chromatography:

• The sample is separated in one direction using one solvent, dried, then turned 90 degrees, and developed in a second solvent. This provides separation based on two different sets of conditions.

Advantages, Disadvantages and applications of Paper chromatography