Sciencemadness Discussion Board

Cheap source for alumina or silica column packing? Also, can you reuse column packing?

alking - 16-3-2016 at 14:05

First I'm wondering if there's a cheap source anyone would recommend for aluminium oxide or silica gel suitable for column chromatography. I see on ebay all kinds of Al2O3 for sand blasting, it's the right grit size, cheap, and in large quantities. I don't see why it would not work for chromatography, however I do wonder if there is a reason we should not use it, primarily heavy metal contamination comes to mind.

Along the same vein if I cannot find a cheap source then I figure I should try to save and reuse my column packing. It would seem easy enough to wash and dry, albeit tedious, however I cannot see how to avoid getting the layers of sand from mixing up in it, which may not matter much at first, but over time it would certainly add up and become more and more of a problem.

Dr.Bob - 16-3-2016 at 16:42

For good chromatography, you need very fine, and consistent sized, particles of either alumnia or silica. The stuff for sand blasting is huge particles compared to for chrom. And sand is basically huge particles of silica, but it does not work well either.

Alumina is cheaper to buy, I think, you can get neutral or acidic or basic, which has to do with how the material is washed after being produced. For purifying amines, basic works well, for acids, the acid is better, as otherwise amines stick to alumina so well they are heard to move in the column, same for acids in reverse. Most heavy metals are not a problem, and most won't dissolve in organic solvents, plus I don't often eat my products.

Silica Gel, what you need depends on if you plan to use flash or gravity columns, flash requires very fine particle size, and clean, dry material to work well.

While it is possible to reuse either material, the results depend on both the amount of crud in the material being purified, as well as what solvents are used to elute them. Alumnia might be easier to wash, dry and reuse; silica gel is harder to wash and reuse, most of it is activated by heating until very dry/activated and that is harder to do after it gets wet with water or other polar solvents, like methanol. But for some uses, it can be reused a few times. It is hard to find cheap good chrom. grade silica gel of any quality. Part of the answer depends on how much you are looking for, grams, pounds or kilos? Part of the task is having a TLC system that works, so you know what material and solvent will work.

BromicAcid - 16-3-2016 at 19:25

A recent thread on reusing column packing:

http://www.sciencemadness.org/talk/viewthread.php?tid=64821

alking - 16-3-2016 at 20:01

Quote: Originally posted by Dr.Bob  
For good chromatography, you need very fine, and consistent sized, particles of either alumnia or silica. The stuff for sand blasting is huge particles compared to for chrom. And sand is basically huge particles of silica, but it does not work well either.


Are you sure about the particle size? From what I've read alumina packing is generally 200-400 mesh size, and the sand blasting alumina I've seen is from 120-320 grit. According to this conversion chart that would mean anything >= 240 grit should work, provided it's consistent as you point out. However seeing how providers seem to carry a range of grit sizes it stands to reason they must separate them to a reasonable degree. Take this ebay listing for example, that seems like it would work well enough to me and it's less than a fourth of the price I've paid for reagent grade alumina. That would only leave heavy metal contamination and maybe an unfavourable ph (I don't know how the industrial stuff is processed to even guess), but neither of those would necessarily be a problem depending on the application

Edit: Fixed quote formatting

[Edited on 3-17-2016 by zts16]

Dr.Bob - 17-3-2016 at 04:27

If you can find the right mesh size that is great. Aluminia should be easy to find cheap than silica gel. But I would still try to buy some good stuff so that you can compare it to the cheap stuff, and get some idea if it is working. And you could theoretically modify the alumnia yourself or just use solvents that make it work OK. Best thing is to find a simple separation that you can test on any material, similar to the test kits they sell for flash chrom testing, used to check automated systems like ISCO or Biotage. Most have either dyes or easy to see by UV compounds like acetophenones with a few very different groups on them, like tert-butylacetophenone, methoxyacetophenone, and dimethylaminoacetophenone, which give three or four various polarities. Nitro compounds work well, as they are are easy to see.

alking - 17-3-2016 at 10:21

That is a good point, and I do have reagent grade already to compare to, which I would certainly use if absolute purity were critical. Since a lot of what I am doing at present is just for expiramenting and educational purposes I'd rather use a cheaper alternative if possible. As cheap as this stuff is it would be worth it just to find out, you could probably get it even cheaper in bulk.

Do you have any info or resources on modifying the polarity of alumina? I remember trying to do a search before and the results were crowded out by irrelevant info and I could not find more specific search terms to help me out. Is it as simple as washing it with the appropriate solution?

Dr.Bob - 17-3-2016 at 10:51

I used "what makes aluminum oxide basic or acidic for chromatography" and found about 10 guides, some of which describe those details of acid/base treatment, and several that give all sorts of details on chrom. with both silica and alumina. One of the first hits was company offering free samples, so take a look, I only looked at the first 20-30 hits.

alking - 17-3-2016 at 15:03

Awesome, thanks. I never considered literally asking a question as a search string, I always thought that was a bad practice for w/e reason.