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Simulations of open tubular chromatography
Two analytes (blue and red) are pushed forward inside a tube. The walls of the tube are marked yellow. When the analytes hit the walls, they may or may not stay there for a while. If the analytes have different preferences to staying at the wall, they can be separated. This is chromatography. All of the below examples were simulated using MATLAB scripts.
All videos by Martin Andersson, created 1999, reformatted 2011.
No flow, no partitioning, diffusion only
Here, two analytes are inside the tube. They bounce at the walls without staying there, and there is no flow. They move only because of diffusion. Diffusion is making the analytes spread out. This one of the reasons for band broadening. Another reason for peaks getting wider occurs if that the analytes stay in at the walls too much, resulting in “tailing” (not shown here).
Flow only, no partitioning, no diffusion
When a sample is injected into the tube, ideally it should be shaped like a plug. If there is no inter-action with the walls while flowing through the tube, and if there is no diffusion, the plug of sample will exit the tube in the same condition as when it entered the tube.
Flow and diffusion, no partitioning
If there is a plug flow and diffusion occurs, but at the same time there is no interaction with the walls, there is no possibility to separate the analytes.
Chromatography: flow, diffusion, and partitioning
In analytical chromatography, the analytes spend most of their time away from the wall. When hitting the wall, they will stay there shortly. If they have different preferences to staying at the wall, they will exit the tube at different times.
Preparative chromatography: flow, diffusion, and strong partitioning
In preparative chromatography, one of the substances has no affinity at all to staying at the wall. The other substance is completely stuck when hitting the wall. In this way, samples can be cleaned up from unwanted substances.
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