The paper chromatography you can do with felt-tip pens looks pretty, but it turns out not to be terribly useful for working scientists. However, High-Performance Liquid Chromatography (HPLC) is the same idea, and it’s used very widely in chemistry. Just like paper chromatography, you use water (or another liquid) as a solvent to separate the components of the material you’re trying to investigate, like a dye. Rather than using tissue paper, you let the liquid flow along a ‘column’ – a thin tube – which is perhaps 10 or 20 cm long. You then investigate the substances which emerge from the end of the column, and how they change over time.
So with pen dye, the smaller pigment molecules would emerge first, with the larger ones making their way out later. Chemists, including environmental scientists, can use HPLC to investigate a wide range of samples.
Gas Chromatography is similar, but the solvent isn’t a liquid, it’s a gas. Because gasses flow more freely than liquids, the columns (tubes) need to be longer to achieve the separation of components – they might be dozens of metres long. Gas Chromatography is also used widely in chemistry.
Thin-layer chromatography is another technique, and it’s like an advanced version of the paper chromatography. It’s used for detecting pesticides or insecticides in food.
All of these methods work by separating out the individual components or parts of mixtures and solutions.