Sciencemadness Discussion Board

Choosing TLC plates

GreenD - 7-11-2012 at 14:35

What are the specs to "standard" TLC plates?

I need to do some synthesis soon, for some aromatic, slightly polar molecules, but nothing too crazy, some sulfonamides.

But I'm battered and beaten with options to choose from on the web (not inexpensive, mind you).

250 thickness* seems standard.
I've liked the polyester backing in the past.

I should avoid "H R F" coatings?? What are these anyways? Why would I need a fluorescent marker on my TLC plate... Seems stupid. To check if your bulb is working?


[Edited on 7-11-2012 by GreenD]

gutter_ca - 7-11-2012 at 14:47

Quote: Originally posted by GreenD  


I should avoid "H R F" coatings?? What are these anyways? Why would I need a fluorescent marker on my TLC plate... Seems stupid. To check if your bulb is working?


[Edited on 7-11-2012 by GreenD]



http://www.sciencemadness.org/talk/viewthread.php?tid=13156&...
Quote: Originally posted by ziqquratu  
DJF90, the idea of shining UV light on the tubes directly will rarely work - when we run TLC, the fluorescent compound is pre-bound to the silica itself (from memory, the most common one is some zinc compound), and the spots we observe under UV light arise through the compounds of interest QUENCHING that fluorescence. Not many compounds fluoresce themselves when exposed to UV light. You can actually see the difference when you DO have a fluorescent sample on a TLC plate - rather than the usual dark purple spot, you observe a glowing spot of whatever colour - purple, blue, green, red, it depends on the compound.

GreenD - 7-11-2012 at 15:43

Gutter you are totally right - my memory fails me. The plates are very fluorescent and bright under the UV light, but the compounds are actual decreases of intensity.

Thanks.

So Fluorescent markers... this pertains to the whole plate being fluorescent or it has its own marker, some sort of control?

DJF90 - 7-11-2012 at 16:40

The whole plates fluoresce green under UV 254nm. Compounds on the plates quench this fluorescence and appear as purple spots. If I remember correctly, the fluorescent compound is zinc sulfide, although I may be mistaken on this. Gypsum is normally used as a binder. The plates I have in front of me now are Machery Nagel Alugram Sil G/UV254 for TLC. G indicates the Gypsum binder, and UV254 indicates the fluorescent additive. Layer is 0.20mm of silica gel 60, plates are 20cmx20cm and you cut them to size (or use as is for prep TLC, although the layer thickness is a bit thin for this).

GreenD - 7-11-2012 at 17:25

Thanks DJF90