Dear all,
Hi, I have a question of F254 silica gel.
Using 254 light, the TLC plate emit green fluorescence(?), but when I did column chromatography with F254 silica gel, I couldn't see that emission.
Is this because of glassware? or is there other reason?
Also, if I can't see this emission and can't confirm the product while I did column chromatography, how should I use F254 silica gel?
Check the solvent utilised for the CC. It could have altered your gel.
One usually doesn't use F-254 for column chromatography. F-254 is used for TLC plates; it works because the UV light is blocked by the sample on top of the plate; with no excitation light, the zinc silicate doesn't glow and you see you compound as black spots. Glass does a poor job passing some wavelengths of UV light. Borosilicate glass, which is used for lab glassware such as columns, doesn't transmit 254 nm. Your solvents may block the light too.
You are better using regular silica in your column and spot the fractions onto TLC plates with F-254 silica.
Methanol too will 'quench' any fluorescence. This is the reason why Acetone is used in the dilution of the chemical Fluorescein.
I would assume that you use glass column that will absorb the light going thru the column and the light emission from the stationary phase.
https://www.quora.com/Why-does-glass-block-UV
Hi Narong thank you for your answer. I think this is the reason I want.
Then, should I order other glass column? is there other kind of glasswares not absorbing UV?
I didn't read what solvents are being used, but the very common ethyl acetate will damage polycarbonate, as would the commonly used hexane and dichloromethane.
https://www.calpaclab.com/polycarbonate-chemical-compatibility-chart/
The aromatic groups in the polycarbonate will also absorb the 254 nm light needed for the zinc silicate to fluoresce.
About the only "glass" that transits UV is quartz.
https://www.coleparmer.com/i/environmental-express-ion-exchange-columns-5-5-ml-with-frit-50-pk/3520043?PubID=UX&persist=true&ip=no&gclid=CjwKCAiA15vTBRAHEiwA7Snfc_oCr1wZqvYMsr1v_Kcs_gH9cLLrFXxOKhNTM8Bto6ysJdLEYf2j7hoCNT4QAvD_BwE
try the above plastic tube. or use TLC plate and scrape if off the plate.
Dear researcher,
as for your concern isolation of molecules with column chromatography: two things must be accounted.
1. particle size of silica, if you choose silica for TLC grade (fine size) movement of solvent will be affected which leads hindrance in separation of molecules, for this some pressure should be applied (as in FLASH chromatography), but for conventional (under gravity force only), 60-120 mesh sized silica is preferred in long column for better isolation.
you can follow "Isolation of antioxidant phytoconstituents from the seeds of Lens culinaris Medik: Elsevier, Food Chemistry. 175, 358–365."
Thank you guys!
I'll check silica particle size and other advices.
Thanks a lot!
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