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Topic: Tailing/Wide Column Chromatography Peaks - How to avoid  (Read 12021 times)

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Offline MorganFreeman

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Re: Tailing/Wide Column Chromatography Peaks - How to avoid
« Reply #15 on: June 23, 2012, 11:28:50 PM »
When I dry load with celite, generally the color of the celite does not change over the course of the elution. I haven't paid much attention, I will let you know more details when I try this again.

By the way, thank you for the help everyone.

Offline Gage

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Re: Tailing/Wide Column Chromatography Peaks - How to avoid
« Reply #16 on: June 30, 2012, 08:41:17 PM »
You might get ahold of some spherical silica, best place seems to be Silicycle.  I used some in the 25-40 micron range and noticed that I had tighter bands and less asymmetry than usual flash silica gives.  The flow rate was less, but not problematic.  It is more expensive ($150 I think for 250 g) but could be worth it for valuable separations.  I have only used it once but was able to pull off a separation that normally would have required more silica.

Another thing you could try if you have it available is radial chromatography.  Those plates use what is essentially TLC silica and give better results than columns.  We use it all the time.

Offline nox

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Re: Tailing/Wide Column Chromatography Peaks - How to avoid
« Reply #17 on: June 30, 2012, 11:45:18 PM »
To be perfectly honest if the product is not a solid and more or less thermally stable, Kugelrohr is superior to chromatography as a purification method. One of labmates swears by it and I think he purified 90% of his substrates this way. (I've read a couple of Org Syn preps where they even purify solids (!) by Kugelrohr. Of course you'll need a very good vacuum pump (<0.1 Torr) to pull off something like that)

Offline discodermolide

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Re: Tailing/Wide Column Chromatography Peaks - How to avoid
« Reply #18 on: July 01, 2012, 03:25:11 PM »
To be perfectly honest if the product is not a solid and more or less thermally stable, Kugelrohr is superior to chromatography as a purification method. One of labmates swears by it and I think he purified 90% of his substrates this way. (I've read a couple of Org Syn preps where they even purify solids (!) by Kugelrohr. Of course you'll need a very good vacuum pump (<0.1 Torr) to pull off something like that)

Sorry I must disagree. A Kugelrohr distillation only removes volatile or non volatile components from the compound. Further the compound is subjected to lots of thermal stress. You may as well set up a proper distillation apparatus.
Better is a short path distillation or even better a spinning band system. But as you say you need a good vacuum, preferentially a diffusion pump.

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