ORGLIST: How to pack a column with TLC grade silica gel?

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From: Alexey Gromov (alexey.gromov$##$
Date: Thu Jan 03 2008 - 02:30:35 EST

Who could give me an advise how to pack a column with TLC grade SiO2 (5-25
micrometer, Aldrich)?
I tried dry packing: applied vacuum (1 mm) from the bottom end of the column
and added SiO2 in small portions, after every portion knocked on the column
with a rubber tube for 20 sec. Also the column looks fine, but the solvent
front goes quite ugly - the shape is like "shark's teeth". Moreover, when I
was passing solvent through the column, "two fronts" appeared: one is the
common one (front of impregnation of SiO2), and the second one is a thin
layer of solvent which goes by walls (between packed SiO2 and glass
surface). This second front goes much faster then the first one.
The column diameter was 0.7 cm.

I also tried "wet" packing of slurry of SiO2 in a solvent, but it's not so
easy to see the solvent front. Moreover, The final voulme of impregnated
SiO2 is the same as in the first case. So, I assumed that the density of
packing is the same, i.e. too low.

Thanks in advance,
Alexey Gromov

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