To unravel the mystery it seems to me that the data presented is missing sort of a crucial piece. The fellow had many samples and much data about what was in the distilled product but what was missing was data about how the distillation was carried out.
A temperature graph of both the heating mantle temperature (which can be smoking hot) and the head temp seem relevant to me. He demonstrated a very clean sample and some not so clean. What I want to know is what temperatures were present during distillation and see if any correlations at all become evident.
This month ran a few grams of some very clear pale yellow second run sublimator med through my LC column. I was shocked that a band of off white eluted well before the D9. I was even more shocked as it evaporated away the solvent that it became a deep purple to the point it was almost black. It was just a trace after evap but I never would have thought to see that come out of such pure looking med. Next month run my SOP is a DCVC run between pass 2 and a third pass I plan. The third pass should work as a standard then and I plan to fire up my 15+ year old spectrophotometer and see what it says. It is a dual beam UV Hach model I got from EBay from a government shop. It is finicky but seems accurate enough.
I have seen hues of purple before come out overnight when the dab is fresh out of the sublimator and left in the freezer too and puzzled over this.
It is hard to see the purple but it is there. Look at the edges more. This dab is just out of the freezer overnight before I learned to keep things under vacuum. Going into the freezer and being frozen it was substantially clear and pale yellow. The camera on my old iPad isn’t that good but I wanted a picture of it. This dab when held in good light had an ever so slight purple hue to it after an evening in the freezer and it was not the first time. I had seen this on all my high purity dabs after an overnight In the freezer (-7C) but then it turns to rose color and red after pretty quick. Always though after a day of running and overnight in the freezer it takes on a slight shade of purple. I told my buddy it was the grape jelly stage though it is just a faint purple. it is a repeatable thing. This purple did not show up in extract held under vacuum but did elute as I said when run in an LC column.
This is a shot of thawed extract that started clear and is just transitioning from very light purple to rose color. This is about one or two days left out in atmosphere, freezer or otherwise.
Weird. Maybe it’s evil… You guys are a smart bunch - what is the purple? I will say that the sample the purple was removed from was the absolute smoothest THC dab I ever had (and I have had a lot). Ideas?
@Beaker I actually do know what is most likely happening to your distillate, but speaking of missing data: I do not know what all your stationary phase (LC column powder) is composed of, but I suspect part of it is alkalinizing your distillate… is there MagSil or other hydroxyl functionality in it? What is your mobile phase (solvent)?
I have a new search term for you: the alkaline beam test …this alkaline test reagent (usually 5% w/v KOH in 190 proof ethanol) reacts deep violet in the presence of CBD, and generates no color in the presence of THC, alone, so it makes for a rather sensitive test for CBD. This alkaline reagent is not the only way to get alkalinity into your resin, causing violet color. For example, MgO (and probably ZnO) in the decarboxylation and/or distillation boiling flask will react with CBD to make the distillate purple in the presence of air while heating. For example, when you have an air/vacuum leak in a boiling flask joint, the reflux ring will turn deep purple.
Any color changes due to pH shifts during temporary presence of water, or even anhydrous (no pH) acid/alkaline colorimetric reactions that take place, as in the example mentioned above, can end up changing the color permanently, even after the acid/alkaline compounds are no longer present, such as after distillate passes up a packed column and through the condenser, leaving all MgO behind. Some are reversible, some are not. In the case of MgO, hot CBD, and air leak combo causing purplyness, the reaction immediately ceases and appears to reverse as soon as you seal the leak. As long as the color did not reach the cooling zones, it probably won’t show up in your distillate.
Interestingly, as most of you may know, the typical color of distilland exposed to air is deep red. This is a more permanent oxidation reaction (which, although somewhat azeotropic, mostly comes over during the final tails higher temperature end of the distillation. This redness involves mainly the phosphatides like lecithin and triglycerides present in the distilland, generally in very low quantities.
I use standard silica gel 60 30-35 micron size from Amazon. My solvent system is a gradient and the column is run as a DCVC column. The gradient goes from hexane alone with increasing ethyl acetate. Hexane alone will not pass the cannabinoid on this gel and it stays on top until the gradient increases. Highly colored compounds precede the cannabinoid. As the gradient climbs to about 15-20% the cannabinoids begin to move. It proceeds from there and I catch fractions one at a time in 20ml test tubes. On raw extract it is amazing how many colored compounds seperate.
In the case of this run the first band to run ahead of the cannabinoid was that layer that evaporated to purple. Now that I know it is there though I know how to get it out. When it turns red with time I just rerun the extract and it leaves the red in the boiling flask.
i think your right about the zinc or metal “Molecular/zeolytic sieves and zinc chloride are employed as a catalyst to aid the reaction. The molecular sieves act as a water binding agent, and the zinc chloride acts as a catalyst to reduce the activation energy required for the cyclization reaction.”
This is a great post for analytical chemists - very informative video.
We have dealt with our fair share of these mystery peaks on our LC chromatograms in distillate samples. I am reaching out to our standards provider (cerilliant) to see if they will add D10/D10aTHC to their radar for future development to help with more accurate quantification.
I think our friends at Infinite Chemical Analysis have isolated the mystery peaks in that region and sent them in for NMR analysis/identification. I believe they are also working on publishing a paper on the topic.
@Future Nah, saponification is probably something you want to avoid, since that would cause your cannabinoids to be micelle-soluble in polar solvents like water… and conditions that caustic should be avoided for other chemical reasons.
I don’t believe you can separate THC from THCA by setting collection for 270nm. They both have large absorbance near that value. Where did you find this? If anything, the separation was due to the chromatography method, not due to telling the system to collect when high 270nm absorbance was detected.
You guys are a smart bunch - what is the purple? I will say that the sample the purple was removed from was the absolute smoothest THC dab I ever had (and I have had a lot). Ideas?
