Easy, quick method for qualitative analysis of CBD in a sample

Data Dump Analytical
1

Stumbled across this a while ago. Tested it, and it seems to work, though false positives are going to be highly likely.

Original called for the following quantities (but I’ve found it can be scaled easily):

500mg NaOH
250mg activated charcoal (not necessary in oil analysis).
35mg flower sample.
91% IPA.
Water.

Procedure is simple, and as I said, quantities can be scaled very easily. As a qualitative analysis there’s no need to accurately control quantities. If we were going to try and validate this method for quantification with some kind of colour chart, then we’d have to be more strict.

  1. Add NaOH + sample to an apppropriately sized vial.
  2. Half fill the vial with 91%+ IPA + shake.
  3. Fill the remainder of the vial with IPA that has been diluted to ~50% with H2O.
  4. Shake, and wait. Purple indicates CBD.

You may notice two layers form depending on amount of NaOH used - NaOH solution and IPA are poorly miscible. You’ll obviously notice the colour change in the top (IPA) layer where your analytes of interest are present.

Original author suggested the use of activated charcoal to give extra clarity and easier spot the colour change when analysing flower samples, however in my efforts, it only seemed to make it even harder to observe any colour change.

There is obviously the potential for false positives here. I tried testing a relatively pure d9 sample, but it turns out my d9 sample had 20% CBD in it after analysis, so the false positive I believed to see for d9 wasn’t actually a false positive, because there was CBD in the sample.

Left = 99.6% CBD
Right = Distillate sample w/ ~70% THC & ~20% CBD.

20180130_111847
20180130_1118473024×4032 2.07 MB

Suspected THC dominant Flower sample with activated charcoal. (You can see it didn’t really help the colour in my instance, but that could be because I didn’t stick to the outlined proportions).

20180130_174027
20180130_1740273024×4032 2.38 MB

Video below showing the start of the gradual change in colour after shaking.

edit: Not sure if embedding of videos is supported here yet. Not sure it’s even necessary. Here’s the link anyway

Video Link

6 Likes
2

I saw this effect described while researching “acid/Base” extractions of thca. its a ph dominated phenomena i think so accurate ph measurements would prob go along way towards standardization. happens at a ph between ~11-14

2 Likes
3

I think you’re right, a constant molar concentration would be very necessary in a validated method. Perhaps a more aggressive solvent to aid in full extraction of analyte from sample might help, and one that was fully miscible with aqueous NaOH solution might mean the concentration of NaOH could be reduced.

Of course the real problem with this as any kind of quantification expreiment is that we’re working with incredibly complex sample matrixes with hundreds of chemically distinct compounds which might or might not be undergoing secondary/side reactions and might also interfere with the visual outcome of the experiment.

With ultra high purity CRM’s, a calibration table and colour chart would be simple enough to develop, but the second you introduce a sample with more than a single cannabinoid presence, any hope of your quantification being accurate will have gone out the window.

Is anyone entirely sure of the chemical reaction going on here?

A friend suggested the basic NaOH solution is converting the phenol group in CBD into its phenoxide anion, which will be coloured in solution. Further hypothesising that each cannabinoid phenoxide will have a varying colour - The more high energy (the more polar the more phenol groups) the more blue/purple it will be, the lower energy, the less polar groups, the more red it will be …And there’s a whole colour spectrum between that.

If anyone has any more input than that, I’d love to hear it.

1 Like
4

Try ethanolic NaOH. It is called the Beam test and I believe it oxidizes CBD’s to their hydroxyquinones.