Question

What would be an explanation/discussion of product isolation? In this case, we are conduction column Chromatography.

Answer 1

Suppose you wanted to separate a mixture of two coloured compounds - one yellow, one blue. The mixture looks green. You would make a concentrated solution of the mixture preferably in the solvent used in the column. First you open the tap to allow the solvent already in the column to drain so that it is level with the top of the packing material, and then add the solution carefully to the top of the column. Then you open the tap again so that the coloured mixture is all absorbed into the top of the packing material, so that it might look like this: Next you add fresh solvent to the top of the column, trying to disturb the packing material as little as possible. Then you open the tap so that the solvent can flow down through the column, collecting it in a beaker or flask at the bottom. As the solvent runs through, you keep adding fresh solvent to the top so that the column never dries out. The next set of diagrams shows what might happen over time.

Note: These diagrams are very simplified in order to make them easier to draw. In reality, the colours won't separate out into these neat blocks, but will probably be much more spread out - more so the further down the column they get.

Explaining what is happening This assumes that you have read the explanation for what happens during thin layer chromatography. If you haven't, follow the very first link at the top of the page and come back to this point afterwards. The blue compound is obviously more polar than the yellow one - it perhaps even has the ability to hydrogen bond. You can tell this because the blue compound doesn't travel through the column very quickly. That means that it must adsorb more strongly to the silica gel or alumina than the yellow one. The less polar yellow one spends more of its time in the solvent and therefore washes through the column much faster. The process of washing a compound through a column using a solvent is known as elution. The solvent is sometimes known as the eluent.