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Author: Subject: Chromatography non-analytical uses
coherent
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[*] posted on 27-6-2023 at 18:03
Chromatography non-analytical uses


I have a question regarding liquid chromatography, specifically the potential application of this technique.

Would it be feasible to use liquid chromatography as a means of seperating a relatively large quantity of liquid, say for example: approx 250ml post-reaction aqueous solution or solid product dissolved in 250ml of solvent?

While it's clear that LC is a great tool for quantitive and qualitive analysis I've been quite interested in how it might perform as a means of seperating substances that would otherwise be very difficult to seperate using more typical methods.

Has anyone experience with this or could provide some insight?
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[*] posted on 27-6-2023 at 18:08


Are you just thinking of column chromatography with silica gel? Where are you coming from with this? People use column chromatography all the time.



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[*] posted on 27-6-2023 at 21:01


As far as I know, column chromatography is a batch process
and the volume of each batch is much much smaller than the column.
So you'd need a gigantic column for 250ml of product.




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[*] posted on 28-6-2023 at 04:37


Generally, you evaporate the solvent off before loading your crude product onto the column. You can’t chromatograph a dilute solution of material, that will just smear it all over the place.



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[*] posted on 28-6-2023 at 05:03


Quote: Originally posted by BromicAcid  
Are you just thinking of column chromatography with silica gel? Where are you coming from with this? People use column chromatography all the time.


Yeah this is exactly what i'm thinking, but more specifically I'm interested in how practical it would be for seperation for the purpose of obtaining a reasonable quantity of usable products, say 100ml minimum?

My very basic understanding of chromatography is that it's typically an analytical tool dealing in small sample quantities, my question is how well this would scale up.
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[*] posted on 28-6-2023 at 05:08


Quote: Originally posted by Texium  
Generally, you evaporate the solvent off before loading your crude product onto the column. You can’t chromatograph a dilute solution of material, that will just smear it all over the place.


Ah yes that would be an issue, I suppose too it would depend also on the difference in retention time, enough time must elapse such that there is complete seperation of products?

I was just curious if this something that would be practical, figured it may be useful in circumstances where other methods of seperation prove difficult, provided you're willing to spend the time doing it...
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[*] posted on 28-6-2023 at 05:37


Yes, please go read up on column chromatography. It’s a very common method. Just not incredibly common for amateurs due to the relatively small scales it’s practical on, and the large volume of often expensive and/or hard to find solvents that it requires.



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[*] posted on 28-6-2023 at 08:10


https://www.youtube.com/watch?v=UmWMlKJAdSk


just multiply the testtube number by 100 :D




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[*] posted on 28-6-2023 at 08:39


I would say if you have 250ml of crude, first use TLC to find conditions that provide effective seperation.
Then concentrate the 250ml to as small a volume as possible, and replacate the chromatography conditions using a full sized column extraction keeping each fraction seperate. You want to split it down into say 50 parts depending on the volume of elluent.
Run TLC on each container of fractionated product to determine what is where. Then combine the relevant fractions and remove the solvent.

I did this a few times at uni for isolation of a reaction mixture. We also ran individual spots of starting materials to ID knowns and unknowns, then we did NMR on the unknown to prove it was the correct substance. Hopefully you can ID your product in a more accessible way :)
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[*] posted on 29-6-2023 at 04:11


Quote: Originally posted by Swinfi2  
I would say if you have 250ml of crude, first use TLC to find conditions that provide effective seperation.
Then concentrate the 250ml to as small a volume as possible, and replacate the chromatography conditions using a full sized column extraction keeping each fraction seperate. You want to split it down into say 50 parts depending on the volume of elluent.
Run TLC on each container of fractionated product to determine what is where. Then combine the relevant fractions and remove the solvent.

I did this a few times at uni for isolation of a reaction mixture. We also ran individual spots of starting materials to ID knowns and unknowns, then we did NMR on the unknown to prove it was the correct substance. Hopefully you can ID your product in a more accessible way :)


Great explaination! thanks for the detail, it's exactly what i'm after. I've only tried paper chromatography (cellulose chromatography paper) but i'm very keen to try TLC, sounds like it'd be extremely useful for checking reaction progress or comparing results when unsure about products. I think i'll need to experiment a bit to get a feel for the processes and their limitations.
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[*] posted on 29-6-2023 at 13:28


I've had several preps over the years where you pass a large amount of material through the a column. It's usually specific to certain impurities, they don't travel through the column and get left behind. You usually still use an elutant to drive the rest of your product through but sometimes you need to actually dissolve in a solvent. There are some amazing things you can do with a silica gel or alumina column if you've got the time for process development. It all depends on what you're trying to remove.



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