Chromatography is a technique used for the separation of a mixture by passing it through a medium in which the components of the mixture move at different rates.

The word chromatography comes from the Greek words chroma, which means color, and graphos, which means to draw. This name was chosen by the Russian botanist, Mikhail Tswett, in 1906. He separated different pigments from a plant extract by loading a sample mixture onto a calcium carbonate column.

Step 1. The stationary phase is packed in a column. The solvent, which is the mobile phase, is poured into the top of the column, goes through the stationary phase, and drips out the bottom of the column. The loaded sample is placed on top of the stationary phase. Step 2. The mobile phase continues to move through the column. The loaded sample begins to progress down the column and there is some separation of the sample. Step 3. The sample has separated into its component dyes. Dye B is further up the column because the dye had a strong interaction with the stationary phase. Dye A is further down the column because the dye had a weak interaction with the stationary phase. The mobile phase which drips out the bottom of the column is collected in containers. This is called fraction collection.

Figure 1. Tswett's method of separating a mixture of pigments from a plant extract.

By passing a solvent (mobile phase) through the column (stationary phase) the different components of the sample moved at different rates down the column due to their chemical and physical properties. As a result, Tswett separated and collected each of the three dye molecules that make up chlorophyll, and developed a now widely used and versatile technique. Today, chromatography is used for the separation, purification, and identification of compounds.

Chromatography principles

Chromatography techniques

Chromatography phases