Well, writing up this blog post somehow slipped through the cracks for a year (Sorry!!), but without further delay, here's how we do the technique.
Step 1: Building the glassware.
We use these columns on crude reaction mixtures from ~10 to ~500 mg scale. For smaller scale than this, we use prep TLC; larger, just a standard reusable column.
To build the column, for 10-50 mg, we just use a Pasteur pipette as the column. For 50-200 mg, we build it out of a 16 X 150mm tube. For 200-500 mg, we build it out of a 25 X 150 mm tube.
For the latter two, the first step is to pull a bottom spout from the test tube. Basically, you heat the tube with a Benzomatic torch, until you see the bottom glow orange and "wilt" slightly. At this point, you grab the glass with a pair of tweezers and steadily pull to make a long stem. It's hard to explain, but easy to demonstrate:
It's a bit tricky the first time, but gets simple with practice.
After letting the tube cool to rt, snapping off the bulk of the stem gets you a nice looking column:
(If you're using a Pasteur pipette, you get to skip to this stage)
Step 2: Building/running the column.
From here, it's just a matter of packing a small chunk of Kimwipe into the bottom, and tamping it down, followed by adding a bit of sand, and then silica gel. With modern silica gel, we have found that even <3" column height is still plenty to do reasonable separations. After equilibrating with a column volume or two of solvent, here's what it looks like, ready to load and use as usual:
One nice thing about the column sizes is that the 16mm tube (loosely) accommodates a 14/20 inlet adapter, while the 25mm tube (loosely) takes a 24/40 adapter. This way, you can run it with positive air pressure exactly as you would any other flash column. This is a 16mm tube, and as you can see, the small inlet adapter fits it nicely:
When the column is finished, here at Scripps, our EH&S allows us to dispose of the whole thing, tube and all, into our silica waste stream. Check with your EH&S for what to do at your institution.
Regardless, the best part of this technique is there are no dishes to wash!
Hope that this helps aspiring chromatographers,