What is Chromatography?

Chromatography is a process that can be used to isolate the various components of a mixture. There are a number of different types in use, including gas, liquid, paper, and gel permeation chromatography, and this process can get quite involved, especially with complex mixtures. It is also an extremely useful addition to a variety of fields, including pure and applied sciences, forensics, and athletics, among others.

The process relies on the fact that different molecules will behave in different ways when they are dissolved in a solvent and moved across an absorbent medium. In a very simple example, one could take ink and make a mark on a piece of paper. The paper could be dipped into water, and the capillary action of the water would pull the ink through the paper. As the ink moved, its ingredients would separate out, revealing a distinctive pattern that could be used to determine the components of the ink.

In preparative chromatography, researchers separate individual components of a compound for use in the lab or in research. This process can get extremely precise: using this technique, for example, scientists can isolate two strands of DNA that differ by only a few pieces of information. In analytical chromatography, the goal is to figure out what is in a sample. Drug testing relies on this technique to isolate illicit substances in urine and blood samples, for instance.

In the example above with a dot of ink and a piece of paper, the basic concepts behind the process are illustrated, although most methods are a bit more sophisticated. It is important to choose the right solvent or carrier fluid to dissolve the sample in and to select an appropriate solid medium to pass the sample through. Poor choices can result in confusing or inaccurate results, and the procedure requires substantial skills on the part of the operator to ensure that it returns useful data.

The result of a session is a chromatograph, a printout that provides information about the substance being analyzed. The printout usually takes the form of a chart with a series of troughs and peaks. Each peak represents a substance present in the sample, and the concentrations of these substances can be determined by looking at the height and width of the peak. Computerized chromatography machines generate such printouts automatically as the data is produced, and they can also be made by hand.