General question, have any of you done column chromatography with small amounts of compounds - 5-20mg?
Old lab used to exclusively do chemistry at 50-100g levels, so learning these smaller set ups has been new.
What size column is appropriate?
Gregkristofvagyok - 13-3-2013 at 13:05
In that size column chromatography is done on the most easy way in a Pasteur pipette.
It could be easily turned into a tiny column and usually works great. The only important thing is to use really fine silica or other adsorbent,
because other way your substance will "fall through" the column.bananaman - 13-3-2013 at 20:12
In addition to the use of Pasteur pipettes, you might want to simply run it on a TLC plate, and subsequently scratch your desired product out later.phlogiston - 14-3-2013 at 02:56
That is not small scale! I routinely do LC chromatography on picomoles of compounds.
But that is for analytical purposes, so its probably not relevant to you.GreenD - 14-3-2013 at 10:24
I have done on pasteur pipettes, but it was only to achieve a truly crude product.
Thanks guys. Its small scale relative to what I am used to work with. Your picomoles are nothing in comparison to when I work on femtomole scales, but
thats for physics experiments which isn't relevant to you.GreenD - 14-3-2013 at 10:26
The only important thing is to use really fine silica or other adsorbent, because other way your substance will "fall through" the column.
Thanks for this. Are the particle sizes of silica gels really only dictators of elution time? Changing particle sizes are really only to improve
purity, would this be a correct assumption, or is there a more important factor in choosing particle size?kristofvagyok - 14-3-2013 at 12:52
Changing particle sizes are really only to improve purity, would this be a correct assumption, or is there a more important factor in choosing
particle size?
Theoretical plate increases if you use more fine adsorbents. If you use a 635mesh instead of a 100mesh than your compounds will separate more easily.
Do you have access to preparative TLC? Usually 1-5mm thin TLC plates could be used perfectly for these like separations as bananaman suggested it. bananaman - 14-3-2013 at 17:06
According to the Van Deemter equation, size of particles would affect the resolution of peaks. The smaller the particle size, the better the
resolution.
If your compounds tend to elute close to each other, you might wish to pack a longer column, or perhaps work on the eluting solvent to determine what
is best for your separation.GreenD - 14-3-2013 at 19:23
Preparative TLC sounds like a great option, thanks very much. smaerd - 17-3-2013 at 04:53
Yea you can always do a streak of product on a TLC plate such as in "preparitive TLC"
Quote:
Ideally, compound should be suspended in organic solvent at a high concentration. Approximately 10
mg may be applied to a 10 x 10 cm plastic TLC plate, 20-30 mg to a 20 x 20 cm plastic TLC plate, and 25-
200 mg to a glass-backed TLC plate.
[Edited on 17-3-2013 by smaerd]jamit - 17-3-2013 at 05:03
How practical is column chromotography for home lab and in separating and purifying Chemicals. I just find it useless on a practical level or am I
missing something here?bfesser - 17-3-2013 at 08:14
You're missing something here. You must not do much organic chemistry.bananaman - 17-3-2013 at 20:25
How practical is column chromotography for home lab and in separating and purifying Chemicals. I just find it useless on a practical level or am I
missing something here?
It all depends on the scale of synthesis. If you are synthesizing stuff in grams and above, then you could either crystallize or distill the desired
product out.
However, when your quantity is low, column chromatography is still a good way to purify things up.
