Gonna run the experiment anyways..... but ETOH chromatography question


#1

Hey friendos,

I’ve ran a couple experiments with a dry loaded chromatography column. I was doing a modified DCVC setup a la @Beaker and had great success with doing a water/etoh gradient. My problem is my alumina is brown/purple and I can’t actually see anything that goes on. So I’m really just trudging into experiments pretty blindly and interpreting results.

If anyone has a good source for alumina hook me up! (I’m in Canada, but can order from U.S. if needed. I’ve got a couple samples coming in from China for pretty cheap).

When at room temperature everything behaved as to be expected and pulled off the red/yellow gradient to great success. When I run the column with super chilled etoh (-40c) I noticed I was getting the chlorophyll/brown gradients first. Can anyone explain why this would be? I had read that some aspects of etoh polarity changes at low temperatures? Would it reverse the process so all my undesireables get eluted on the first pass?


#3

My supply of white alumina dried up. I think carbon chemistry sells activated alumina which is likely white. Activated might not make a difference with a reverse phase sort of chromatography but who knows. No idea why you see differences that you do with a temp change. I always run stuff at ambient. @Shadownaught might know and might also have a source.


#4

Email elsie@elchemicalinc.com I’ve been talking to her, she’s sending me some kg samples for basically just the shipping cost. I do intend to buy larger, but they’re pretty good with sending cheap samples if you pay shipping. Just ask for the mesh and colour of alumina and go from there! I got her contact from sifting through 30+ vendors on alibaba lol.


#5

Like @Beaker mentioned we do sell Alumina. You can see a list of our products on www.carbon-chemistry.com and contact us through there. We normally sell bulk materials, but if you only need a smaller volume then the sales team can line you up with one of our retailers.


#6

TLC is the answer.


#7

TLC is marginal at qualifying cannabinoid profiles but is completely inappropriate for obvious reasons to prepare compound. These posts have to do with using chromatography in general for preparing compound much like a filtration process.

Further, according to the University of Copenhagen who hosted a video describing DCVC, TLC does not resolve as many compounds in some cases as DCVC. DCVC because of an easily tunable solvent gradient can actually reveal more compounds than TLC.

The vast majority of posts on the internet from the ever growing number of legitimately informed users that describe various chromatography techniques other than Gas Chromatography are nearly always describing preparatory chromatography which DCVC is far and away suited better for preparing bulk compound than any other method.:nerd_face:


#8

Right. As the fractions come out of your column you can test each fraction by TLC. I’ve found toluene to be a good solvent for TLC. Just make sure you let the solvent dry as toluene is uv active. If you do a good job on your column you can qualitatively tell what is in each fraction (Do I have one spot or three). Then get the fractions tested by mass spec or something and you have two pieces of data for potential confirmation of desired product(s). Are you doing normal or reverse phase chromatography? Alumina suggest normal phase.


#9

But the mobile phase is clearly reverse phase. Is this what’s ruining the alumina?


#10

I run standard phase DCVC over silica gel 60 with an ethyl acetate/hexane gradient and have run reverse phase style of filtration using alcohol and water over standard alumina.

TLC is simply not a tool that is useful in this endeavor because this endeavor is strictly preparatory and meant only to fraction compound. Adding a step to see if one, two, or many spots pop up provides no feedback that will alter the procedure because the procedure is largely a filtration as used. As an acedemic exersize it is often suggested of course and in a lab wanting to qualify a cannabinoid profile it can help but TLC will generally not resolve compounds as well as DCVC. The fellow in Denmark commented that often he will run a TLC on a sample and show one or two compounds the run DCVC and discover yet another. So TLC in many cases does not have the resolution anyway comparatively.

Mostly though if a process like testing serves no purpose towards the seperations of the compound in any given month I rarely engage in it. In other words I know that what I want elutes between highly colored carotenoids up front and will overlap a bit the green bands that need highly polar solvent to even move through the column. Experience tells me where things elute and for testing in the beginning I would test with the highest precision available - I would purge each fraction of solvent and vape each color band individually. This is the kind of testing I see very little of online yet is by far more revealling. It is just not revealling in a way that can be photographed or taught from a textbook. But for sure once you vape the different colored bands then you will know at a core level what you have. TLC of course cannot provide the lungs on experience with the downside being I must use my body to test instead of a piece of paper.


#11

You talking prep TLC or quantitative?


#12

Ethanol and water you say?? This would be so much easier on my pump than heptane/ethyl acetate. I’m guessing you would use ethanol to get the celite to absorb the extract, then dry load and proceed as you would with heptane and ethyl acetate in a DCVC run?


#13

That’s what I do to great success.

I’ve been running all of my gradient chilled, I find I keep a higher % alcohol and it moves through the column a bit slower, I’m also just guessing, but I think it sticks some wax in the column.

I usually start with the dry cake, then run water over it until it runs clear.

I have my gradient all at about -14c starting with 60/40 etoh/water for a single pass

Then 70/30 x1
75/25 x2
80/20 x2
85/15 x2

Then usually just run warm etoh to clear the column after that. I usually have all the desirable compounds out by the second 85/15 pull. Though obviosuly load and material dependant.

I do the cold pull because it makes for easier evaporation as well since we’re dealing with higher % alcohol so in turn lower boiling point/energy required to evaporate off the solvent (though I guess there could be an argument made to run it at lower abv at room temperature and then you’ll just have more water and the oil likely sitting at the bottom). I’ve been running it cold with pretty good success though.


#14

Thanks for that breakdown! So I should expect green chlorophyll fractions to come out first, followed by brown, red, orange, then yellow, correct? I have brown 240 grit alumina on hand so I’m considering playing with this method very soon. Sounds like this would also save a ton of money on media compared to using silica.


#15

So pending on the brown alumina you might notice some smell from the industrial processing. I end up needing to use about 30L of water to 1kg of alumina to fully clean it. I just put it in a column and vacuum flush water over the alumina until there’s no smell noticed.

It proceeds in a common fashion with the chlorophyl and darkest compounds coming off last. It usually runs through a gradient of yellow, orange, red, and finally brown then green.

So I’m not 100% sure on the science. @Beaker has written a couple times that the etoh/h20 creates a reverse phase column. I’m of the (ill founded) opinion it might have more to do with a “solubility” gradient since water doesn’t dissolve the thc, so the increasing alcohol starts to pull more and more through the column, but I have zero chemistry background other than self study and doing well in high school. I was thinking since most people do a methanol//EA gradient and only doing it up to 40% methanol and a column clean with a highly non-polar solvent; we’re not running the exact same polar to non-polar ratios; but we’re still getting the same result on a similarily phased column. Again, I don’t understand the science exactly, I just know it’s been working :stuck_out_tongue: Though I supposed you’d need to measure the polarity of 60% etoh up to 95% etoh to get a defiinitve answer, but I don’t think 60% etoh would be on the opposite end of the polarity spectrum as 95%.


#16

I’m excited to give it a whirl! I’ll probably wait until I get a smaller column though, since all I have right now is a 1-liter funnel. Much less costly and frustrating to learn on a small scale. I found this article while searching for an appropriately sized funnel though. Figured I’d post it here since it goes into detail about media size and such.

https://erowid.org/archive/rhodium/chemistry/equipment/dry-column.vacuum.chromatography.html