Young cannabis confirmed: Cannabinoid content discriminates between drug and hemp forms of cannabis seedlings

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  • Published: Apr 16, 2012
  • Author: Steve Down
  • Channels: HPLC
thumbnail image: Young cannabis confirmed: Cannabinoid content discriminates between drug and hemp forms of cannabis seedlings

Cannabis or hemp?

The major cannabinoids of cannabis plants have been measured for seedlings and plants at various stages of growth using HPLC, to establish when the plant can be confidently identified as a drug-type plant, as opposed to other chemotypes like hemp.

Seizures of cannabis plants are on the increase in Europe, thanks partially to the growth in indoor production under controlled conditions. It is now commonplace to read news reports announcing the discovery of cannabis farms in houses in urban areas, so widespread has the practice become.

Mature cannabis plants are easy to recognise but in some countries, where hemp cultivation is legalised, it is more difficult to determine whether seized plants are the drug-type or fibre-type (hemp) cannabis. The flowering portions of mature plants provide one means of discrimination but this may not be possible for younger plants.

In this case, it is more reliable to perform a chemical analysis of the cannabinoids present. These are the characteristic set of compounds which are unique to cannabis plants but which vary sufficiently with the particular chemotype to allow them to be distinguished.

This route has been followed by scientists in Belgium, who have employed the content of particular cannabinoids to determine the chemotype of cannabis plants of all ages, from seedling to mature plants. The authorities often have very young plants to identify in seized batches, so they must be able to carry out typing with confidence. The key question is whether or not the same rules can be applied to young plants as mature plants.

Benjamin De Backer and Corinne Charlier from the University of Liege and Kevin Maebe and Alain Verstraete from Ghent University published their findings in the Journal of Forensic Sciences.


Cannabinoid content

The main psychoactive component in cannabis is tetrahydrocannabinol (THC) and it has a closely related acid, tetrahydrocannabinolic acid (THCA). The total concentration of these two compounds is relatively high in the drug form, ranging typically from 2-20. A third compound, cannabinol, is formed by the oxidation of THC and is found in relatively high amounts in aged cannabis.

Cannabidiol (CBD) is the major non-psychoactive cannabinoid and it is more dominant in the hemp form of cannabis. It is formed by decarboxylation of the related compound cannabidiolic acid (CBDA).

Earlier studies had established that the ratio of THC+THCA to CBD+CBDA is an accurate indicator of chemotype. The drug-type plants had ratios far greater than 1.0 and a CBD+CBDA level less than 0.5% of inflorescence dry weight. Conversely, the hemp plants had a ratio much lower than 1.0. There is also a third chemotype with an intermediate ratio in the range 0.5-2.0%.

De Backer and his team acquired three sets of plants from the Belgian Federal Police that are normally cultivated in Belgium, although they probably originated in the Netherlands. They were grown under controlled conditions mimicking those used by illegal indoor growers in western Europe.

Every week, young shoots and leaves were collected for analysis, along with the flowering sections when they had grown. The samples were dried and extracted for analysis of the cannabinoids by HPLC with diode array detection at 211 and 220 nm for the neutral and acidic compounds, respectively, using a method they developed in 2009. HPLC was preferred to GC methods due to the gentler thermal nature of the analysis.


Distinctive when young

The three sets of plants had comparable cannabinoid content. The THC+THCA content followed the same pattern although the maximum values differed, probably due to the different potencies of the varieties. The values rose gradually during the peak budding stage before maximising five or six weeks after flowering at 19, 16.5 and 22.5% dry weight before falling away with age.

The only cannabinoids found in the seedlings when they were received in the lab were THC and THCA, at a level of 0.2%. Their ages were unknown but the team estimated them to be 1-3 weeks old. One week of cultivation raised the level to 1.62%, confirming that the plants were of the drug variety.

Examining the weekly THC and THCA levels, De Backer declared that the chemotype of drug-type cannabis varieties can be established in seedlings that are as young as three weeks post-germination, corresponding to the third or fourth leaf stage. So, there is no need to wait for the inflorescence stage for identification

For two of the plant sets, the concentrations of CBD and CBDA were below the detection limit and only a small amount of CBDA was measured in the third set at the end of the reproductive stage of growth. The researchers agreed with reported conclusions that no plants grown for their high THC content will have THC+THCA/CBD+CBDA ratios typical of the hemp form of cannabis.

So, although the THC+THCA/CBD+CBDA ratio could not be measured in most cases due to the low CBD+CBDA levels, the absolute amounts of THC+THCA were sufficient for classification.

This simple method will be suitable for establishing the identity of drug-type cannabis in seized plants as young as three weeks old. Conversely, it could also be used to establish the legality of the hemp-type cannabis for growers in countries where hemp cultivation is permitted.

Related Links

Journal of Forensic Sciences 2012 (Article in Press): "Evolution of the content of THC and other major cannabinoids in drug-type cannabis cuttings and seedlings during growth of plants"

Article by Steve Down

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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