Paper chromatography

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T.baccata-paper chromatography

Paper chromatography is an analytical chemistry technique for separating and identifying mixtures that are or can be colored, especially pigments. This method is used to separate chemical compounds from a mixture by distributing the compounds between two phases: a stationary phase and a mobile phase. The stationary phase in paper chromatography is a piece of high-quality filter paper, and the mobile phase is a solvent or mixture of solvents that moves through the paper by capillary action.

Principles

The principle behind paper chromatography is based on the relative solubility of the compounds in the mixture and their affinity towards the stationary and mobile phases. Compounds that have a higher affinity for the stationary phase will move slower, while those with a higher affinity for the mobile phase will move faster. This difference in movement allows the compounds to be separated as they spread out on the paper.

Types

There are two main types of paper chromatography:

• Ascending Paper Chromatography: In this method, the solvent travels up the paper strip by capillary action.
• Descending Paper Chromatography: Here, the solvent moves down the paper strip, aided by gravity and capillary action.

Procedure

The basic steps involved in paper chromatography are as follows:

1. A spot of the mixture to be analyzed is applied near the bottom of the paper.
2. The paper is then suspended in a container with the solvent or solvent mixture. The spot should be above the level of the solvent.
3. The solvent moves up the paper by capillary action, carrying the compounds with it.
4. As the solvent continues to move, the compounds in the mixture separate based on their affinity to the mobile and stationary phases.
5. After the solvent has traveled a predetermined distance, the paper is removed and dried.
6. The separated compounds can then be visualized, often by using UV light or by staining the paper.

Applications

Paper chromatography is widely used in various fields for qualitative analysis, including:

• Identifying compounds present in a mixture.
• Purification of compounds.
• Determining the purity of substances.
• In biochemistry, for separating organic and inorganic compounds for analysis.
• In forensic science, for analyzing the components of inks, dyes, and other substances.

Advantages and Disadvantages

Advantages:

• Simple and inexpensive.
• Requires small sample sizes.
• No need for complex equipment.

Disadvantages:

• Not suitable for large-scale separations.
• Limited resolving power compared to other chromatographic techniques.
• Quantitative analysis is less accurate.

See Also

• Chromatography
• Thin layer chromatography
• Gas chromatography
• High-performance liquid chromatography