[teejay0023]

Folks,

Does anyone know a good stain (preferably a general stain) that can be used to visualize compounds on a silica-coated TLC plate that has been pretreated with an organic base such as triethylamine?  Sometimes as you know you need to add a few percent TEA to get polar compounds to move. Or, your stuff is unstable on regular silica.  In grad school I would run a blank plate in eluent plus 1-2% TEA, then spot my unstable crude and run the plate.  This would preserve the integrity of my compound and thankfully it was UV-active.  But occasionally I want to use TEA to run a plate AND I need to stain it.  The TEA sticks to the plate and prevents visualization with a KMnO4 stain, etc.  I tried using isopropylamine, which has a low bp (31-35C), and heating the plate before staining it, but still no luck.  The base sticks tightly to the plate and washes out your ability to visualize anything.  If anyone can suggest a solution for this that can be used with classic TLC plates I would be very appreciative.

Thanks.

[Dan]

Cerium ammonium moylbdate (CAM). I'm sure there are others, but I only really use CAM and permanganate.

Also, you can heat the plate strongly, or put it under vacuum for a while, to drive off all the TEA before dipping in other TEA-incompatible stains (like permanganate).

[teejay0023]

Great, thanks Dan.  I've used CAM a few times.  Probably I didn't heat the plate for long enough to drive off the base before staining with KMnO4...

I like vanillin as a stain quite a bit.  You get all the colors of the rainbow, and sometimes with very close running spots you can see a distinct color difference that can be helpful.  Also it smells great when you heat it.

Cheers