In the several years that I tutored at the 1st-year help center, I’ve always had students who find thin-layer chromatography mystifying.  Most of these students don’t “get” what the plates are doing, or the role of the eluent.  For whatever reason, the physical analogy of things getting washed away and gripping the ground (or the inability to do so) seems to help in guiding the thought process.  I drew this up should you, as either instructor or student, would find this helpful.  Lo!  Behold the whimsical…

As usual, clicking on the figure opens a larger version for viewing.  A PDF version for print is available here. I’m not too happy with the final output – I feel as if the spatially-suggested connection between the analogy and the phenomena to be explained is not clear enough.  Suggestions to make this more useful / analogy more clear is appreciated.

Update (17 Dec 2011 Revision R3): The addition of the imagine/now consider label seems to clear up the analogy-phenomena.  I thank Loïc Samuel for the suggestion.