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Author: Subject: What is the difference between flash chromatography and dry chromatography?
wg48temp9
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[*] posted on 6-3-2021 at 04:19
What is the difference between flash chromatography and dry chromatography?


I have looked up what the difference between dry vacuum chromatography and flash chromatography is. Apparently the only significant difference in the apparatus is the column in dry chromatography is packed dry with some compression. Do I have that correct ?

So given the same amount (mass) and type of the stationary phase with identical column diameters and solvent, the separation with both will be very similar. Is that correct?




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[*] posted on 6-3-2021 at 07:40


Quote: Originally posted by wg48temp9  
dry chromatography is packed dry with some compression.


How to pack probably depends a lot on the silica gel available and the difficulty of separation. The original lit. speaks of this "cheaper" TLC-mesh gel. Maybe it was all fines from making larger sizes then. Probably became more expensive and hard to find quick. Especially without additives. Maybe if you own a ball mill...

There's many ways to do column chromatography. The only difference is the column is run dry, since pressure was never a requirement for other forms.

https://www.erowid.org/archive/rhodium/chemistry/index.html

the chromatography section




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[*] posted on 6-3-2021 at 08:11


The way that I typically set up a column is I first add the amount of silica gel that I want to use. Then I add enough solvent to the column to make a slurry of the silica, and shake it until it has all become a nice slurry. Then I let it rest for a few minutes to equilibrate and let the solvent soak into the silica gel (this is important because otherwise you’ll get a lot of air bubbles). Finally I apply compressed air to finish compacting the column and push out any excess solvent until the top of the silica is exposed but not dry. Then I add my sample as a solution in as low of a polarity of solvent as it is readily soluble in, and gently apply compressed air until it is loaded onto the column (once again, the top of the silica should be exposed but still moist). Then I add a little sand and carefully pour in the first round of eluent, and it’s ready to run.



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