Acid chlorides [August 26, 2004]
Posted: Sun Aug 29, 2004 8:49 pm
By mmm on Thursday, August 26, 2004 - 11:25 am:
I wondered if any could expand on the idea of analyzing acid chlorides without derivitization.Two of the impurities we are looking at derivitize into the same tri-ester.We have also tried normal phase HPLC (the main component is an anhydride)but response factor is unpredictable.This is espicially true for the main component.As the purity gets higher from 98%-99% the main component practically disappears.I was using a silica column, but will try a CN column to avoid any possible reaction with the silica.
Any information on a GC or LC method would be helpful.
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By Uwe Neue on Thursday, August 26, 2004 - 02:34 pm:
Bonded phases also contain silanols. Since your compounds are very sensitive, it may not be possible to do this with retention LC. Are there any significant molecular weight differences between the compounds that you are trying to separate?
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By Zelechonok on Friday, August 27, 2004 - 03:47 am:
Your silica column has some water even in normal mode conditions. For this reason, try to add about 1% of acetic anhydride to the mobile phase. Theoretically you may be able to remove some water and mask active silanols with in situ silica ester formation. The polar component of the mobile phase beside acetic anhydride should include aprotonic solvent like MTBE or THF (no EtOH). I never did this experiment myself, but I see no reason why it should not work. Tell me if you get any result
I wondered if any could expand on the idea of analyzing acid chlorides without derivitization.Two of the impurities we are looking at derivitize into the same tri-ester.We have also tried normal phase HPLC (the main component is an anhydride)but response factor is unpredictable.This is espicially true for the main component.As the purity gets higher from 98%-99% the main component practically disappears.I was using a silica column, but will try a CN column to avoid any possible reaction with the silica.
Any information on a GC or LC method would be helpful.
-------------------------------------------------------------------------------------------------------
By Uwe Neue on Thursday, August 26, 2004 - 02:34 pm:
Bonded phases also contain silanols. Since your compounds are very sensitive, it may not be possible to do this with retention LC. Are there any significant molecular weight differences between the compounds that you are trying to separate?
-------------------------------------------------------------------------------------------------------
By Zelechonok on Friday, August 27, 2004 - 03:47 am:
Your silica column has some water even in normal mode conditions. For this reason, try to add about 1% of acetic anhydride to the mobile phase. Theoretically you may be able to remove some water and mask active silanols with in situ silica ester formation. The polar component of the mobile phase beside acetic anhydride should include aprotonic solvent like MTBE or THF (no EtOH). I never did this experiment myself, but I see no reason why it should not work. Tell me if you get any result