Classification of Chromatography

Introduction

Chromatography is a laboratory technique, especially in the analytical field used to separate a mixture of components present in a chemical species. There are different types of chromatographic techniques

For the separation of mixtures into their units in the laboratory, the chromatographic technique is used. So, the method which involves the separation of a specific mixture into its respective elements is given the name chromatography. It is done by using a mobile phase and stationary phase. The mobile phase carries away distinct components through the stationary phase present in a mixture because the effect of the solvent is different for different components. So, some elements will tend to move faster, and some move slow. That component has a particular Rf value. And based on the Rf value the chemical components can be easily distinguished.

Column Chromatography Definition

Column chromatography is a chromatographic technique developed by the petroleum chemist D. T Day in the year 1900. The separation technique used in the analytical field that can be used for the separation of a wide variety of components present in a mixture is column chromatography. The name column chromatography is present because of the reason that the stationary phase used in this technique will be a column of adsorbent and the mobile phase will be solvent. The mobile phase will continuously flow through the column, and it will result in the separation of components present in the mixture. The column used contains solid particles packed in the tube. Different mobile phases can be used for the separation of components. The mobile phase commonly used are water, benzene, toluene, ester, acetone, ether, carbon tetrachloride, etc.

Types of Column Chromatography

Column chromatography is further classified into 4 types. They are,

• Adsorption chromatography − In this type of chromatography the stationary phase used is a solid adsorbent. While the mobile phase is a liquid. And the sample needed to separate and is in a solution form. It is used generally for checking the purity of chemical compounds.

• Ion exchange chromatography − In this type of chromatography the stationary is an ion exchange resin while the mobile phase is a liquid solvent. The sample that needed to separate is in the solution form. It is used for the separation of charged biological molecules such as proteins, amino acids, etc.

• Partition chromatography − The stationary phase is an immiscible solvent in the solid matrix. And the mobile phase is a liquid solvent. The sample that needed to separate is in the solution form. It is generally used for the identification of impurities and drugs.

• Gel chromatography − The solvent which is held in the interstices of the polymeric solvent is the stationary phase. And the mobile phase is a liquid solvent. The sample that needed to separate is in the solution form. It is generally used for the separation of molecules of different sizes.

Principle of Column Chromatography

This chromatographic technique includes a stationary phase as a column of adsorbent which contains small solid particles coated on a glass or a metal column. The main principle of this technique is the differential adsorption taking place in the solid phase. The small solid particle presents inside the column act as a thin film too. The mobile phase or eluent and mixture of analyte is then enacted to the column with the help of a pumping system or with the use of gas pressure. Then the solvent will flow through the column and the components present in the mixture will be separated based on their distribution coefficient. Thus, the separation of distinctive components present in the mixture will take place. The separation of components in a mixture is taking place according to the adsorption rate.

Application of Column Chromatography

There are many applications for column chromatography. Some of the applications are,

• It is used for the separation of biological metabolites from biological fluids

• For the analysis of drugs during formulation.

• It has applications in the food industry for checking purity.

• Used for the sanctification of natural compounds obtained from plants.

• It can be used for the separation of active constituents.

• It can be used for the determination of fluocinolone, dexamethasone, etc. in formulations.

• This technique can separate many hundreds of components that are unknown too.

• Few amounts even in the parts per billion ranges or picogram can be detected with this technique.

• It is also used for the separation of final products in organic synthesis.

Advantages of Column Chromatography

Column chromatography has many advantages. Some of them are,

• It can be used for the separation of several complex mixtures.

• There is no limit on the amount of mixture taken to separate.

• The mobile phase is in a broad range.

• It runs automatically.

• This method is robust.

• The analytes separated from the mixture can be reused too.

Disadvantages of Column Chromatography

Even though it has many advantages, it also has some disadvantages. They are,

• The separation time is taken by this method more compared to other techniques.

• As it is automatically working it is very expensive.

• Many solvents are required for the separation.

• In comparison to another advanced separation technique, this technique has low separation power.

Conclusion

The chromatography technique is used for the separation of mixtures into respective components. Column chromatography is a type of chromatographic technique. In column chromatography, a column of adsorbent is used as the stationary phase and a solvent is a mobile phase. From which components are separated. Based on the type of stationary and mobile phase used, column chromatography is also classified into 4 types. The principle behind all the column chromatography is the same. Gel chromatography, partition chromatography, ion exchange chromatography, and adsorption chromatography are types of column chromatography. It is an important chromatographic technique, so it has many advantages and disadvantages too. The application of column chromatography is very wide, it is used in the food industry, pharmaceutical industry, etc.

FAQs

1. What factors affect column chromatography?

Some factors affect the column chromatography process. They are,

• The dimension of the column.

• The particle size of the adsorbent.

• Pressure.

• Temperature.

• Nature of solvent

2. What happens when column chromatography runs dry?

Poor separation of components in the mixture will result when the chromatography runs dry. The column commonly used is silica, when dried will result in cracking and it will then affect the outcome or result.

3. How does particle size affect column chromatography?

The size of the particle which is used for the separation of components will easily affect the efficiency of column chromatography. The separation will become more efficient when we use small particles.

4. Why is silica gel used in column chromatography?

Silica gel is used in column chromatography since silica is a compound that has a higher adsorption affinity. And it is an easily available and economically benign substance.

5. How does increasing column length affect chromatography?

The increase in column length used in the chromatographic technique will make the separation of components more efficient. The reason for this is that column length and retention time are directly proportional. Peak broadening is also observed when someone uses a column with increased length.