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Colorimetric THC testing at home

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Rising Star
Hi friends :)
I would like to test my saliva for THC but ready-made tests for sale are very expensive if you want lots of them (best price I found is £100 for 25 tests).
So I thought perhaps I could make them myself, DIY-style. :d
My Google searches yielded Fast Blue B and Duquenois-based methods as my best bets for reagents. Fast Blue B is a bit pricey (plus harder to find worldwide and perhaps a "watched" chemical?) so I'd avoid it if possible.
My question is: how sensitive would Duquenois-based tests be?
I would like the test to react to ~15ng/ml, like the tests used by police officers around here. Is that feasible? Any tips?
Thanks in advance. :love:

Colorimetric tests are the simplest method of identifying cannabinoids. Hundreds more sophisticated analytical methods have been developed, as a review of Chemical Abstracts will reveal.

The Beam test is relatively specific. It gives a purple color with 5% ethanolic KOH, based on the oxidation of CBD, CBG, etc., and their acids to hydroxyquinones. However, THC does not react to the Beam test. Only two plants (Rosemary and Salvia) out of 129 common species tested give a weakly positive reaction. Among some 50 pure vegetable substances such as mono- and sesqui-terpenes, aromatics, etc., only juglone, embelin, and alkyl dioxyquinone develop a color reaction close to that of Cannabis. The reaction is not always dependable; it can be absent if the ethanol is hot. (22, 23)

A modification of the Beam test uses absolute ethanol saturated with gaseous hydrogen chloride. When added to an extract of suspect material, it gives a cherry red color which disappears if water is added. However, the test also gives more or less similar red color reactions with pinene, tobacco, julep, sage, rosemary, and lavender, etc..

The colorimetric test of Duquenois and Moustapha is not so specific as the Beam test, but it is very sensitive. The test reacts to CBN and CBD, but not to THC:

Vanillin (0.4 gr, acetaldehyde (0.06 gr) and 20 ml 95% ethanol is stored in a bottle. Extract the plant material with petroleum ether, then filter it and evaporate the solvent. Add exactly 2 ml of reagent and 2 ml concentrated hydrochloric acid. Stir the mixture; it turns sea-green, then slate gray, followed by indigo within 10 minutes. It turns violet within 30 minutes and becomes more intense.

The Duquenois-Negm hydrogen peroxide/sulfuric acid test is suitable for following the development of the resin and its potency. Macerate cannabis in chloroform or light petroleum ether for several hours. Evaporate 0.2 ml of the extract in a porcelain dish. Add 2 drops 30% hydrogen peroxide and 0.5 ml concentrated sulfuric acid. Rotate the dish gently, and observe the color of the liquid after 5 minutes. A pink color indicates CBD; blood-red color indicates a high concentration of THC. Violet or strong brown indicates THC. CBN produces a green color which quickly turns green-brown.
This is interesting and semi-relevant as I'm currently working on (I hope quantitative) estimation of CBD in a veg oil substrate. The veg oil is a problem though. Looks like I'll have to do some kind of chromatography.

Thanks for the data, sorry for partial thread-jack!

Looks like I'll have to give that Beam test a go. Will run it against a veg oil blank.
@downwardsfromzero: why is that? Oil is soluble in ethanol/naphtha/fuel, no? My lawn mower says yes.😁
If not, why not check for CBD before dissolving in veg. oil?

I read somewhere along the way that to quantify a colorimetry test, one might use a single-color chart (e.g. 100 shades from white to strong-pink if you want to test for CBD with the Duquenois-Negm process, according to my copy-paste).

I see now that there is a cannabis sub-section, not sure why I didn't find it when I posted, sorry for misplaced posting. :oops:
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