Sciencemadness Discussion Board

Preparation of magnesium silicate and/or activated alumina (and others) for chromatograpy

goldberg - 13-9-2018 at 03:15

I have enough gridning silica gel for chromatography in ball mill. It works but it is slow, ball mill requires maintenance etc.
I'm not sure if i should ask this question there or in reference forum, if i'm wrong sorry in advance.

So i tried to look for method of preparation materials that after reaction will be ready for separation without grinding.

I found mentions about synthetic magnesium silicate and activated alumina, they both look promising.
Unfortunately i did not managed to find anything better that commerital materials promoting a few products, MSDS and two patents that were not helpful.
Preparation of ready to use silica gel would be fine too.

I know what chemical reactions are occuring but i have no information about conditions that will allow me to achieve nice, porous structure. And this is whole trick how to find right conditions.

Also preparation of monolith would be awesome but i only found one route for silica monolith that base on rather expensive and non OTC precursor(did not remember detail right now).

Has anybody experience with this topic?
I am ready to carry out a bunch experiments on my own but i need direction in which i should look.

Harristotle - 13-9-2018 at 04:22

I used regular talcum powder, non-scented, purchased from a woodworking shop.

I gave it a wash in some acetone, and then some water, then dried it in an electric frying pan.

Good to go, for TLC, with just a little gypsum.

I used vanillin/h2so4 and an hardware grade 2100 watt blow heater to develop. It worked well.

I have also used this for regular (flash) column chromatography to separate the organic acids from blueberry (I think anthocyanin) pigment. Works well as a simple redox indicator, with potato skin extract slowing the rate of formation of the brown form in the presence of H2O2, but that is another story!

Watch the talc dust - some old stuff is said to be contaminated with asbestos fibres. Regular safe handling and non-breathing of dust should be fine!

goldberg - 13-9-2018 at 05:29

Thanks. I will check how cosmetic grade (becouse i have it right now) will perform.
How about reproducibility of results?
I hoped that with precipitation of my own stationary phase i can control conditions and have relatively this same product each time.

Thanks for tip with stain reagent. I will look for source of vanilin and try it.

JJay - 13-9-2018 at 05:57

I have been wondering about this also. When doing column chromatography (which I have never done), the column adsorbent should match the adsorbent on TLC plates used to verify the purity of fractions, right?

I don't understand why commercial adsorbents are so expensive.

DavidJR - 13-9-2018 at 08:34

Quote: Originally posted by JJay  
I have been wondering about this also. When doing column chromatography (which I have never done), the column adsorbent should match the adsorbent on TLC plates used to verify the purity of fractions, right?


That depends on what you are trying to achieve. If you're doing a TLC to find a mobile phase mixture that will give good separation in a column, then yes, you'll want to use the same stationary phase.

However, in other situations it can be beneficial to use different mobile/stationary phase. For example, you may have a mixture where two components co-elute using your chosen stationary/mobile phase. If you take a fraction containing these components, and then run a TLC with very similar conditions, you might not be able to separate the two components. Using very different chromatographic conditions is likely to alter the selectivity (separation factor, alpha) so might reveal that your "single peak" is actually two or more compounds.

Disclaimer: I have also never done traditional gravity column chromatography nor TLC, however I have learned a lot from having HPLC facilities in my garage.
Quote: Originally posted by JJay  

I don't understand why commercial adsorbents are so expensive.

Plain ol' silica (for normal-phase chromatography) is pretty cheap. Bonded phase materials (e.g. C18/ODS which is commonly used for reverse-phase chromatography) require exotic reagents to prepare and are not cheap.

JJay - 13-9-2018 at 08:48

I've done TLC but not column chromatography nor HPLC. It looks to me like even plain old silica gel is expensive... I've seen prices of in excess of $40 for 500 grams. That seems like a lot for what is essentially a piece of equipment that I will use once and throw away. Chromatography grade alumina is dozens of times as expensive as a technical grade.

Oh, I am pretty sure you would have already tested out the adsorbent/solvent mixture with TLC before running the column, but it does depend on what you are doing. My thoughts were that once you run the column, you want to take the fractions that you've collected and figure out what is in them, perhaps testing each fraction simultaneously on one big plate. You will already have some notion of what fractions have what components, but TLC would let you make sure that you didn't cut a fraction in the wrong spot.


[Edited on 13-9-2018 by JJay]

DavidJR - 14-9-2018 at 05:04

Quote: Originally posted by JJay  
I've done TLC but not column chromatography nor HPLC. It looks to me like even plain old silica gel is expensive... I've seen prices of in excess of $40 for 500 grams.


I bought some "silica gel powder for column chromatograpy" from an eBay seller a while ago (for non-chromatography uses) - it wasn't that expensive. I think I got 500g for £13 or thereabouts.
Quote: Originally posted by JJay  
I've done TLC but not column chromatography nor HPLC. It looks to me like even plain old silica gel is expensive... I've seen prices of in excess of $40 for 500 grams. That seems like a lot for what is essentially a piece of equipment that I will use once and throw away. Chromatography grade alumina is dozens of times as expensive as a technical grade.


Why use it only once? HPLC columns are expensive but are reused many times (though they do have a finite lifetime). If you're doing column chromatography, rinse the column by passing plenty of excess solvent through, and store wet with solvent. Not sure how well it'd work if you tried to completely elute the sample out of a TLC plate to then reuse the plate though.
Quote: Originally posted by JJay  

Oh, I am pretty sure you would have already tested out the adsorbent/solvent mixture with TLC before running the column, but it does depend on what you are doing. My thoughts were that once you run the column, you want to take the fractions that you've collected and figure out what is in them, perhaps testing each fraction simultaneously on one big plate. You will already have some notion of what fractions have what components, but TLC would let you make sure that you didn't cut a fraction in the wrong spot.

In that situation I don't think it's necessary (or even desirable) to use the same stationary phase.

Dr.Bob - 14-9-2018 at 11:22

The cost comes down to what quality you want. Flash silica gel is made to tight (and very fine) particle size specs. purity is very high, and is has already been activated by heating and drying. You can get bags of sand for cheap, which is nearly the same chemically, but it won't separate much in a column. Flash silica can be reused in some cases, depending on the use, solvents, and how picky you are. But it is not easy to do repeatably and reproducible.

Same goes for alumina and other materials. No different than a bag of charcoal and a diamond, same basic stuff (you can cook a hamburger on burning diamonds if you have the money), but the costs vary wildly.

If anyone here wants to play with small amounts of silica gel, I have some small pre-loaded flash silica gel columns I am happy to share, I have thrown some in with previous orders as samples. They are 4-50 grams each, ideal for 100 to 500 mg samples, or simple demos in classes (separation of dyes in kool aid with alcohols). They are not for medical or drug use, may be old and not as active, and most will require you to rig some sort of solvent flow apparatus. But the price is right.

I also have a small amount of C18 modified silica, ideal for reverse phase HPLC type work. If anyone in the US wants a sample or a column to test, let me know what you are thinking of, and I might be able to help. Might even be able to help people outside the US, but the postage may be painful. Good luck.

JJay - 14-9-2018 at 12:20

Quote: Originally posted by DavidJR  
Quote: Originally posted by JJay  
You will already have some notion of what fractions have what components, but TLC would let you make sure that you didn't cut a fraction in the wrong spot.

In that situation I don't think it's necessary (or even desirable) to use the same stationary phase.


My concern would be with the amount of time and effort required to find multiple eluent/stationary phase combos that appear to work acceptably well, but once they are found, by using them in combination, you might observe substances that couldn't be detected by TLC on one phase alone.

I've been looking at columns lately... I might take you up on that silica gel.

goldberg - 15-9-2018 at 00:28

I'm curious if flash chromatography has advantages over TLC for analytical purposes. Theoretically i can attach to it various detectors...

How about mixing waterglass (sodium silicate solution) with sodium carbonate and heating?
Sodium carbonate will liberate CO2 upon heating and sodium silicate reacts with CO2...
And maybe add some agent that will aid making pores?
Had anybody tired to prepare silica gel/something similar in nature from sodium silicate solution?

Or maybe try with some polymers? Polyurethane?
Or maybe make ester of some long polymeric alcohol (like startch or celulose) and then estrify it with higher carboxylic acids?
Making esters of celulose is tricky topic, maybe other alcohol? Erythrytol? Polyvinl alcohol?

DavidJR - 18-9-2018 at 05:21

I've seen PTFE powder available on eBay at relatively low prices. I imagine that might work quite well for reverse phase chromatography......

edit: what about activated carbon powder?

again, I have not tried these, they are just random ideas.

[Edited on 18-9-2018 by DavidJR]