Chromatography: Separating Chemicals in a Mixture
Chromatography is a technique that separates the different chemicals in a mixture by allowing them to pass through two phases: the mobile phase and the stationary phase. The components of the mixture are separated because those that have a stronger affinity for one of these phases will move along at a faster speed than those with a weaker one.
Types of Chromatography
There are several types of chromatography, including paper chromatography and gas chromatography. These techniques are used for separating organic compounds and inorganic chemicals in labs across the world.
The Principle Behind Chromatography
The principle behind all chromatography is that there is a stationary phase that does not move and a mobile phase that does. The stationary phase is typically a solid, such as silica gel or aluminized aluminum sheets, and the mobile phase is usually a solvent that flows through the stationary phase to carry away the chemical compounds from the sample.
Purification Techniques
Some chromatography techniques are used for purification, such as solid-phase extraction or high-pressure liquid chromatography (HPLC). These methods have their own specific applications and are useful for determining the molecular weight of proteins, the concentration of salt in an organic solution, and the tertiary structure of a protein.
Column Chromatography
The most common form of chromatography in laboratories is column chromatography, also known as gas chromatography or liquid chromatography. In this type of chromatography, the stationary phase is packed into a column and the mobile phase is poured slowly into the column.
Thin-Layer Chromatography
Another chromatography technique is called thin-layer chromatography, also known as gel permeation chromatography. In this method, the mobile phase is poured into a column that contains small molecules with small pores and larger molecules have large pores. The molecules with the largest pores will permeate the porous solid, while the smaller ones will be trapped inside the gel particles and will not elute out of the column.
Thin-layer chromatography can be performed by using a plate of glass coated with a very fine layer of silica. The chromatography solvent will then be dipped into the plate and a capillary action will run up the surface of the glass to pick up the mobile phase and carry it along.
Advantages and Applications
The main advantage of this technique is that it allows you to get a very quick snapshot of what is in the mix without spending a lot of time or money. It is often used in the laboratory to determine the presence of sugars in a food or to test for traces of certain drugs.
Chromatography is used in a variety of ways to help in the analysis of complex materials, such as pigments. It was developed in the late 19th century by the Russian botanist Mikhail Tsvet and is still widely used today to separate plant pigments, such as carotenoids and chlorophylls.
Modern chromatography has many uses, from the analysis of total petroleum hydrocarbons to a wide range of other chemicals. The technology is still relatively young and there are many new and exciting developments in the field of chromatography that will continue to improve over the next few years.
