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Author: Subject: Best locking mechanism for glass Flash Chromatography? Keck clips don't work.
beerwiz
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[*] posted on 4-8-2018 at 19:46
Best locking mechanism for glass Flash Chromatography? Keck clips don't work.


I ran my first glass flash column today and I secured (held it in place) the reservoir and the gas inlet adapter at the top with plastic keck clips. When I connected the air compressor, the air inlet adapter came off from the pressure eventhough it was secured by the keck clip. I had to hold it in by hand but that's tedious for long periods of time. Is there a better/proper locking mechanism to hold the reservoir and the gas inlet/flow control adapter in place at 1-2mbar?
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UC235
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[*] posted on 4-8-2018 at 21:22


I think you may be using way too much pressure.
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Sulaiman
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[*] posted on 4-8-2018 at 23:44


For my 24/29 glassware I used plastic Keck clips,
they work quite well with the few Quickfit pieces that I have,
but work poorly with some of the cheap Chinese joints,
because the wide ends of the cheaper joints are not 24.000 mm diameter,
so some joints have the inner part protruding a little, which is ok,
but some have the outer part protruding which means there is no continuous pressure exerted by the Keck clips.

IF this appears to be the problem then;

. use a few turns of plumbers ptfe tape on the inner joint,
this makes the inner joint protrude from the outer,
allowing the Keck clip to exert a continuous pressure on the joint.
The ptfe tape forms a better seal than grease.

. use stainless steel Keck clis that can be bent/modified to keep pressure on a joint.
The stainless steel Keck clips can tolerate higher temperatures and more agressive gasses or liquids that may escape from the joint.

If you clamp the column well but allow the weight of the reservoir to press down on the column then the joint should withstand quite high pressure.

If all else fails then maybe try partial vacuum instead of positive pressure ?
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Metacelsus
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[*] posted on 5-8-2018 at 05:26


UC235 is right. If the pressure is too much for Keck clips, then it's too much pressure for flash chromatography. What kind of stationary phase and column are you using?



As below, so above.
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beerwiz
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[*] posted on 20-9-2018 at 16:51


The solution to this is to use keck clips + use chromatography glassware that has ears, and use multiple rubber bands on the ears to keep them together.
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Dr.Bob
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[*] posted on 20-9-2018 at 17:45


I've rarely had a keck clip pop off, so I agree that you may be using too high a pressure. I always open the flow controller first, clip it on, then slowly increase the pressure on the column. Unless you are using super fine (20-40) silica gel, you only need enough pressure to keep the flow moving, which is about 5-10 psi for 60 mesh silica.
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Sidmadra
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[*] posted on 20-9-2018 at 17:47


Don't people generally use plastic columns for flash chromatography? As a rule of thumb I wouldn't put any laboratory glassware under pressure unless it is specifically designed for that (pressure flasks). Otherwise, you are asking for the glass to explode sending shards of glass flying everywhere, potentially blinding you, scaring your face permanently, or killing you.

Someone posted on here once saying they accidentally had a piece of glassware under pressure or something, and it exploded and sent shards flying everywhere. Cut them in several places and supposedly just barley missed an artery. If the glass had hit a few inches away from where it did, they would have bled out right there before they could even call an ambulance. Glassware under pressure can be scary stuff, even the smallest most innocent pieces.
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Heptylene
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[*] posted on 21-9-2018 at 09:36


Pressures used for flash chromatography are really low, much less than an atmosphere.

When I was in an organic chem lab at uni I used a few party balloons to regulate the pressure that goes into the column. The air source went to the column via a T adapter. To the T adapter I had attached party balloons (4 of them, inside each other to create a higher pressure). The result was that the air couldn't have a higher pressure than tolerated by the balloons. The balloons also served as an air reserve, so I didn't have to pump as often.

Sometimes I even used unregulated N2 to run the column so this served as a safety feature. The balloon would pop before the glass did.

EDIT: Btw the safety part was important because the column we used had a threaded joint at the top. So nothing would pop off to save you if the pressure got too high.

[Edited on 21-9-2018 by Heptylene]
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