Paper Chromatography - Principle, Procedure, and Applications

Introduction

Paper chromatography is a powerful and simple separation technique that has been used for many years in the scientific community. This technique involves separating a mixture of different substances by their movement along a paper strip.

The movement of the substances is due to the differences in their solubility in a given solvent.

In this article, we will explore the principle, procedure, and applications of paper chromatography in detail.

Principle of Paper Chromatography

Paper chromatography is based on the principle of differential solubility. The stationary phase in this technique is a piece of filter paper, and the mobile phase is a liquid solvent. A small spot of the mixture to be separated is placed on the filter paper, and the paper is then placed in a solvent.

The solvent moves up the paper by capillary action, and as it moves, it carries the different components of the mixture along with it.

The movement of the different components is based on their solubility in the solvent. The more soluble a component is, the further it will move up the paper. The less soluble a component is, the less it will move up the paper.

Procedure of Paper Chromatography

The procedure for paper chromatography is simple and straightforward. The following is a step-by-step guide on how to perform paper chromatography.

Step 1 : Prepare the Stationary Phase

Cut a piece of filter paper to the desired size. The size of the paper depends on the amount of the mixture to be separated. The paper should be long enough to hang over the edge of the container holding the solvent.

Step 2 : Spotting the Sample

Using a capillary tube or micropipette, spot the mixture onto the filter paper. The spot should be small and concentrated. The spot should be allowed to dry completely before proceeding.

Step 3 : Preparing the Mobile Phase

Prepare the mobile phase by pouring a small amount of the solvent into a container. The level of the solvent should be below the spot on the filter paper.

Step 4 : Placing the Paper in the Container

Place the filter paper in the container with the solvent. The paper should be held in place so that it does not move.

Step 5 : Developing the Chromatogram

Allow the solvent to move up the paper by capillary action. The solvent will carry the different components of the mixture along with it. Once the solvent has reached the top of the paper, remove the paper from the container and allow it to dry completely.

Step 6 : Analysing the Chromatogram

The chromatogram can be analysed visually or using other methods such as UV or fluorescence spectroscopy. The different components of the mixture will appear as spots on the paper. The distance travelled by each component can be measured and used to identify the component.

Applications of Paper Chromatography

Paper chromatography has many applications in various fields, some of which are discussed below.

Separation of Amino Acids

Paper chromatography is commonly used to separate amino acids. Amino acids can be identified by their characteristic Rf values, which are the distances travelled by the amino acid divided by the distance travelled by the solvent.

Forensic Analysis

Paper chromatography is used in forensic analysis to identify drugs, poisons, and other substances. The characteristic spots on the chromatogram can be used to identify the substance in question.

Food Analysis

Paper chromatography is used in the food industry to analyze food additives and identify any contaminants present in food. This technique is also used to identify the different pigments present in foods such as fruits and vegetables.

Environmental Analysis

Paper chromatography is used to analyze environmental samples such as soil and water to identify pollutants and other contaminants.

Pharmaceutical Analysis

Paper chromatography is used in the pharmaceutical industry to analyze and identify different compounds and their impurities. This is particularly useful in drug development and quality control.

Chemical Education

Paper chromatography is a common experiment in high school and college chemistry courses. It provides students with hands-on experience in separation techniques and can help them better understand the principles of chromatography.

Advantages of Paper Chromatography

There are several advantages of using paper chromatography, which include:

Simple and Inexpensive

Paper chromatography is a simple and inexpensive technique that can be performed with basic laboratory equipment. This makes it accessible to a wide range of users, including students and researchers with limited resources.

High Separation Efficiency

Paper chromatography can separate a wide range of compounds with high efficiency. This is due to the high surface area of the filter paper and the ability of the solvent to penetrate the paper and interact with the compounds.

Rapid Analysis

Paper chromatography can provide rapid analysis of a mixture, with results obtained within a few minutes. This makes it useful in time-sensitive applications, such as in clinical or forensic analysis.

Non-Destructive Analysis

Paper chromatography is a non-destructive technique, which means that the sample can be recovered after the analysis. This is particularly useful in cases where the sample is rare or expensive.

Disadvantages of Paper Chromatography

There are also some disadvantages to using paper chromatography, including:

Limited Separation Power

Paper chromatography has a limited separation power compared to other chromatographic techniques such as high-performance liquid chromatography (HPLC) and gas chromatography (GC). This means that it may not be suitable for complex mixtures.

Limited Quantitative Analysis

Paper chromatography is not a quantitative technique, meaning that it cannot be used to determine the exact amount of a compound in a mixture.

Sensitivity Issues

Paper chromatography may not be as sensitive as other chromatographic techniques, meaning that it may not be able to detect low levels of a compound in a mixture.

Conclusion

Paper chromatography is a powerful and simple separation technique that has many applications in various fields, including forensic analysis, food analysis, and pharmaceutical analysis. It is a versatile technique that can be performed with basic laboratory equipment and provides rapid analysis of a mixture.

However, it also has its limitations, including its limited separation power and quantitative analysis capabilities. Overall, paper chromatography is an important tool in the analytical chemist's toolkit and is likely to continue to be used for many years to come.