Guide to Chromatography
What is chromatography and how does it work?
Chromatography is most simply, the separation of a mixture into its component parts. The mixture being analyzed is dissolved in the mobile phase, which will then carry the mixture through the stationary phase.
See our chromatography terminology guide for definitions.
Each component in the mixture will interact with the stationary phase differently which causes them to be separated from each other. The properties of the mobile and stationary phases will determine the rate at which each component travels. The time travelled is termed the retention time.
The three basic components of chromatography are:
• The stationary phase which is always either a solid phase or a liquid layer which is adsorbed onto a solid surface.
• The mobile phase which is always either a liquid or gas
• The separated molecules
What are the different types of chromatography?
Paper chromatography is the type of chromatography which most people are familiar with. It is a technique which separates soluble chemical substances by the different rates at which the components travel across chromatography paper.
Thin layer chromatography is similar to paper chromatography – however instead of paper a thin layer of alumina or silica gel is coated onto a sheet of thin glass or plastic. The mobile phase can be a singular solvent or a mixture of solvents.
High Performance Liquid Chromatography (HPLC) – this type of chromatography uses liquid as the mobile phase which pushes samples through the column by use of a high pressure pump.
Gas Chromatography (GC) uses an inert gas such as nitrogen or helium as the mobile phase and the stationary phase is contained in a column which is found inside an oven within the instrument.
What is chromatography used for?
Chromatography is used in many different industries such as oil & gas, environmental, pharmaceutical, agrochemical, forensics, food & drink and pesticide industries.
The purpose of chromatography is to separate, identify and assess purity of components within a mixture for qualitative and quantitative analysis.
How can chromatography be used to test the purity of a substance?
Material purity can be determined by the use of chromatography. The higher the purity of the material the less impurities that will be present i.e. there will be fewer peaks on the chromatograph.
Can chromatography be used to separate volatile substances?
Volatile substances can be separated by gas chromatography – the technique analyses volatile substances in the gas phase.
Gas chromatography works by dissolving the sample in a solvent and then vaporizing the sample in order to separate the analyte. Gas chromatography can only be used to separate volatile analytes – if the analyte is not volatile we can use derivatization extraction techniques to put the analyte into a more volatile form which will therefore be more amenable to analysis, or use HPLC as the chromatography technique.
