I have not tried to isolate THC a.
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Good questions. Long answer.
I foresee you would not dry load for a big batch. At my scale it adds inconvenience to dry load in exchange for a more technical and crisp seperation. This might be important for analytical purposes but it would surely get in the way of a production environment.
Wet loading really is very simple and it can be done without sacrificing resolution, especially when we are preparing it and not analyzing per se. It is just a bit tricky to explain really and you kind of have to just do it to see. I can run a short vid on how I can easily wet load onto my column if it helps. Remember though that I am using silica gel 60 and do not have experience with other types.
To wet load the silica gel column I disolve the compound in the bare minimum of hexane needed to be able to suck up everything in a large pipette. The gel column will have a sand layer on top so the column is undisturbed while loading. Then you evenly apply the compound to the top of the sand.
This is where nuance sort of comes in. I have learned that silica gel 60 passes no cannabinoids when hexane alone is the solvent. This is why the gradient starts with hexane alone. In fact almost nothing in the concentrate crude I get passes with any speed at all with just hexane. So the wet load is then pulled down with vacuum into the sand layer and onto the top of the column.
This is the nuance part. To get it going into the gel I add one or two milliliters of the more polar solvent directly onto the compound. It is stuck otherwise. Normally I run Ethyl Acetate as the polar solvent but have used Acetone too with good success. Adding the small amount of the polar solvent to the load will allow the compound to begin moving into the gel albeit slow. Then the gradient is run as normal.
The thing about vacuuming the column dry is that any banding that takes place from wet loading (the one or two milliliters to get it going throws it off a bit) are virtually negated because as each fraction becomes more polar (ethyl acetate) and less non polar (hexane) the top part of any banding is quickly pulled down by vacuum into the main layer. There is a point that trying to pull too much compound through the gel can load the column and cause problems as well but at large scale I have no idea what you would see.
Determining the fractions was pretty easy. I evap all dishes separately, or at least did when starting. Carotenoids and the like, usually bright yellow to orange ride at the front of the solvent gradient and elute first. The cannabinoids almost overlap the carotenoids/terpene fraction and come second with the THCa eluting first but overlapped by the rest of the cannabinoids. It is a deep brown fraction. After that comes the green, pink, and other things.
Is was obvious after two runs which dishes contained the cannabinoids because I start with 60% nominal THC so I know the big fraction must be cannabinoid. Plus that fraction was sticky and left sticky residue to the touch. Carotenoids and terps leave residue but are not sticky and the first highly colored fraction always evapped to just a trace if caught soon enough. Originally for testing after I purged each fraction, even the green ones, I vaped each different compound that seperated. It was immediately obvious to me that once past the brown fraction there was nothing left of interest.
Lab testing is absolutely the best method of testing medicine except for one - personal vaping. Lab tests cannot tell you how it tastes or what it feels like. I do not TLC. I can identify the fraction with THCa because it is the only fraction that after evaporation of solvents that the oil becomes full of bubbles from slow decarboxylation.
Adding additions like acetone are the kinds of tricks you pick up on for a particular compound. However your ratio is very high. 3-5% acetone just by itself with hexane will begin moving all the cannabinoids too slightly and if added on top of ethyl acetate you may actually see reduced resolution. I have tried it lolz (great minds think alike, eh?) Modifiers are sort of tricky and add one more thing to each fraction but maybe there is just that right combo that works better? Trying to use solvents other than room temp is another example of a modifier that might work wonders but adds complexity. I have to kick myself to keep things as simple as possible. 
WhewâŚI gotta vape now. 
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have u ever thought about using tunable solvents for chromatography? i know u probably dont hav access to all the equipment for co2 but im interested in how u would go about it if u did cause thats im trying to work out lol
I have not considered CO2. My next departure from a standard two solvent gradient is planned to be an addition of vinegar at very small %. I have 35% vinegar (acetic acid 35% and 65% water) and will try 1% of this vinegar to my solvent system.
That is about as exotic as I will get I think. My logic is that THCa might associate much better with acetic acid than the other cannabinoids. If so then the hope is the THCa will seperate better because of this at the front of the solvent gradient. It would have to be added to the ethyl acetate during the gradient run.
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Could you ever elute cannabinoids through silica gel with just 100%nonpolar solvent?
If it is possible it would be very slow. For me the stuff sticks on the column with just hexane.
Is this because these media are desiccants?
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Meaning youâve past non polar cannabinois through with 100% non polar solvent?
I choose a size that is easy to compute the gradient. I use 20 ml test tubes to collect each fraction as it comes off. For smaller samples of a few grams I found 20 ml solvent gradients useful. Easy to calculate too. One milliliter equals five percent by volume so running a progressively more polar solvent with each gradient 5% stronger is simple.
However I found for me packing just a bit taller and running 50 ml at a time is less frantic and handles a high column loading of crude a bit better. Remember for this the column gets pulled dry but also remember that the first 100 ml or so of solvent with a column like that is going to get absorbed onto the column gel and not elute. So the first fractions added to the top wonâ t necessarily elute. 50 ml at a time is also easy to compute with each ml being 2% by volume.
I have discovered the solvent gradients that work well for the concentrate I run so I often now skip a step but not at first I didnât. For me I find a 5% Ethyl Acetate (or Acetone) with hexane gets the compound moving and allows for seperating of some pretty bright colors (likely caratanoids and flavonoids). Depending on how things are moving I then normally skip to 15% or 20% EA to Hexane which will move the cannabinoids off. The greens and much more polar solvent loving parts of the compound take a minimum of about 50% EA to hexane. Some tenacious parts need 10% methanol to EA to move off.
When I collect with no intentions of saving the column I stop after the brown cannabinoid band. Generally for a column the size of mine I use about 12 test tubes total to collect all the needed fractions. It takes about double that many if you decide to flush the column.
When performing a run on already purified extract I do not skip solvent gradient steps like I do with crude.
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The column runs like that because of packing. Here is how I pack and it nails it every time. Everything is dry loaded. No solvent or vacuum at first.
Sand layers are optional. Sand layer on the bottom is against the frit. The glass flares just a bit at the bottom to accommodate the frit and a sand layer is used to get the bed for the silica up past that small change in column diameter. Nothing is slowed by sand much so this is effectively making the glass frit much thicker so it is high enough that the bed reaches past the small change in column diameter. Without this the silica gel column narrows at the bottom and it impacts resolution. Uniformity in column and flow is key.
Have at least 200 ml hexane (or your preferred most non polar solvent) ready.
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Dry load sand bed on frit (optional but explained). Use a cork round bottom flask ring holder to tap firmly on the top of the column in order to get the sand as level as possible. Just bang away at it until the sand gets level.
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Now pull the vacuum. Tap all around the column with the cork to get the sand to settle. Stop vacuum.
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Now dry load the silica gel. I have been shooting for half way up or so. Itâs a little much but easier to pack when up that far. Just scoop it in dry. Now it is like the sand layer. Use a cork ring to tap around until it is as level as you can make it.
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Now pull vacuum at highest vacuum setting. Bang away at the top of the column with the cork ring. The silica gel will settle. I then use a wooden dowel that started life as the wooden rod in my closet to hang clothes on lolz and has been cut to about a foot in length and sanded very smooth to pack the gel. Hold the column with one hand and pack straight down and without twisting in a very firm manner. The gel should compress nicely and keep the vacuum on.
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Take a small spatula with a tip bent at 90 degrees. A steel table knife with a tip bent at 90 would do. Use the tip to carefully compact all around the sides of the column. Make it as firm as you can. The packing rod cannot get the edges of the gel against the sides and the sides are the problem area. Pack just as firmly in tiny steps all away around as the main body and against the glass. Use the spatula to gently smooth any bumps on top. Get it very flat and even and packed. Keep vacuum going.
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Cut filter paper to cover the silica gel and place on top of the gel. Turn the vacuum down to the lowest setting now. My gauge reads 5 psi vacuum at this point for this. I use a funnel above the column in a clamp directly centered on the column. The hexane now is poured in continuously via the funnel through the column under vacuum until the solvent line is all the way through and eluting. Pull then the solvent all the way through until it is more or less dry. The column is now packed. If the solvent descended perfectly even and in a straight line all the way through to the frit ⌠success!!!
I then prefer a sand bed on top of even the filter paper but no more tapping and such. Just drop in a dry layer on top of the gel and use your spatula to gently even it out. A quarter inch or so is plenty for a sand layer. Then dry or wet load the compound onto the sand and you are ready to proceed.
The whole idea is attempting perfect uniformity with how the solvent flows as it hits the gel and perfect uniformity of the gel from top to bottom of column. So a funnel keeps the solvent pouring uniform onto the column and the filters and sand serve also to protect the column from solvent turbulence. How to dry or wet load is another topic. Here is a solvent polarity chart. When I speak of polar or non polar solvent this is the basis of that.
I reuse the column if I can for roughing but not if cross contamination is an issue.
You can see for yourself. After a run flush the column with EA and methanol until clean. More methanol than 10% wonât hurt things really but the silica gel bead form some sort of weird colloidal with high concentrations and can end up in your compound. Technically I do not believe the gel is miscible in methanol but when I used it straight at 100% for flushing the column sure enough on evap some silica gel traces ended up eluting. You do not need more than 10% methanol anyway but 100% flushes a column real good lolz. For flash chromatography using more than 10% methanol causes the gel to swell and cracking in the column occurs which is a catastrophic fail for flash. For DCVC we pull it dry each time so cracking like that is of no concern, at least for flushing.
Anyway keep the vacuum on until the column is very dry after all solvent is running clear. Then come back the next day. Pull 100% acetone through the dry column. You will see likely a bunch of color elute. There is always at least some hold up in the column. It is almost cheaper to load a fresh column than it is for the solvent to flush the column.
Acetone is a non polar solvent and is miscible in hexane like ethyl acetate. It works in substantially similar fashion to ethyl acetate but there are differences in how it fractions. I have used dichloromethane as well which seems to work if you can get around the sweaty sock stink. Of course combos of more than two solvents are possible and used all the time. Adjusting Ph with something is an option too but really just learning how to run a clean column with a simple gradient gets the job done.
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Would quartz silica sand hold on to polar molecules simular to the silica 60?
Silica Gel is pretty benign stuff and is safe to use around food and drug items. Quartz silica is different. It is dangerous to use around things meant to be inhaled. Quartz silica can lead up to a dangerous lung condition and is a known and serious health hazard this way. The stuff damages lung tissue. In my opinion it should not be used in a process like this with a drug meant to be inhaled.
Interesting silica gel has no Silicosis effects?
No. Quartz silica is responsible for that disease and not silica gel. If silica gel caused it then I doubt it would be allowed at all in labs and schools. It would be treated like airborn asbestos and shunned in those places I think.
https://www.osha.gov/OshDoc/data_General_Facts/crystalline-factsheet.pdf
I ask because Sigma-Aldrich warns to not inhale the silica 60 powder
Is it just me or are these pictures unavailable?
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We had a technical hiccup that has since been resolved.
@beaker has been awesome about rebuilding his posts.
Here is a video that my iBook creater app made for me. It is a cool app because it will spit out an epub, ibook, or make it into a video like here. So this is in book format. I do all my work at home on an iPad plus I vape a lot. This means lolz that there are typos and such a lot but this video demonstrates the basic idea.
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Are there supposed to be pics??