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Chromatography generally designs techniques for the separation of compounds inside a mixture. In fact, there are different kind of chromatography like, paper, thin layer and column chromatography. Column chromatography, also called Flash Chromatography (or liquid chromatography) is the most useful methods for the purification and the separation of mixture, because you can use it for both analytical and preparative applications. With this technique, you can purify both solid and liquid compounds. The separation mechanism involves the same principles as Thin Layer Chromatography (TLC) but it is not restricted by quantities to be separated. But how does column chromatography work? Almost all types of chromatographic techniques are based on the affinity of the compounds for the mobile and stationary phases, resulting in the emergence of products from the stationary phase at different speeds. Typically flash chromatography consists in loading a crude reaction mixture to the top of a stationary phase, most of the time silica gel, and elute it with a solvent. This will let the different compounds of the mixture interact with the silica. At the end, if you chose the right eluent and stationary phase, you should separately collect pure products.

Before doing the purification by flash chromatography, you should first determine the experimental conditions by using thin layer chromatography. With TLC you will know how many products are in your crude reaction and you will be able to determine the relative polarity of each one. So let have a brief overview of the thin layer chromatography technique.