Chromatography is a widely used separation method in the world of science and research to separate mixtures. This method can also be used to demonstrate certain substances in a mixture. It is widely used in chemical laboratories and has various methodologies.
There are different forms of chromatography. Each form is based on the principle of a mobile and a stationary phase. The mobile phase is the gas or liquid that moves along the stationary phase during chromatography. The mobile phase carries the mixture that is to be separated.
In addition, a distinction is made between preparative chromatography, in which a component must be purified from a mixture, and analytical chromatography, in which it is determined which substance is present and in what quantity.
There are different methods to perform chromatography. In paper chromatography, thin layer chromatography and column chromatography the mobile phase is a solvent. If the mobile phase is a gas, it is gas chromatography.
When using paper chromatography – the simplest form of chromatography – a mixture passes through a solid layer, for example paper or an aluminium oxide gel. The various particles in the mixture are absorbed or not by the solid layer. Thin layer chromatography is based on the same principle but is used more in laboratories.
Another method based on absorption is gas chromatography. A carrier, usually a porous solid, is placed in a spiral tube. An inert (non-reactive) gas is forced through the tube. Using a micro flame or another detector at the end of the tube, the composition of the mixture can be determined. Gas chromatography is used, among other things, to determine solvents in groundwater and surface water, to detect drugs or explosives and the composition of natural gas.
The separation methods High-performance liquid chromatography (HPLC) and Ultra high performance liquid chromatography (UHPLC) are forms of liquid chromatography. The eluent – the medium to transport the sample to be analyzed or separated over the carrier – is pumped through a column under high pressure. Silica is often placed in the column as a stationary phase. The composition of a sample can be investigated using various detection methods, including spectrophotometry and mass spectrometry. HPLC and UHPLC are widely used in medical labs and the pharmaceutical industry, among others.
In column chromatography, a glass tube is filled with a special mixture of, for example, sand or a certain gel. A mixture is placed on top of that, which then seeps down. By collecting a sample in a test tube at the bottom, the mixture can be analyzed, partly due to the time in between.
Components that each have a different charge can also be separated using electrophoresis. By applying a charge to a carrier, positively charged particles are attracted to one side, and negatively charged particles to the other side. Uncharged particles do nothing. This method is used, for example, to separate amino acids and proteins or to perform DNA research.
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