Analysis of cannabis, cannabis resin and cannabis oil
The presence of cannabinoids in suspect material can be indicated by the Duquenois–Levine test. A sample of cannabis, cannabis resin or cannabis oil (3–5 mg) is first extracted with petroleum ether (0.5 mL). The solvent is removed and the extract is evaporated to dryness. The addition of Duquenois reagent (five drops) followed by concentrated hydrochloric acid (five drops) yields a purple colour after a few minutes. The addition of chloroform (0.5 mL) should result in the purple colour moving into the chloroform layer, which can be taken as good evidence for the presence of cannabinoids. Extracts can also be analysed by TLC.
Microscopic examination of cannabis and cannabis resin As discussed earlier, the cannabis plant is characterised by cystolithic and glandular hairs, with the cystolithic hairs containing a deposit of calcium carbonate. To carry out the microscopic test, place a small portion of the dry material (cannabis herbal material or cannabis resin) on a microscope slide. Identify the cystolithic and glandular hairs. Add a few drops of Duquenois reagent (Moffat et al. 2004) followed by a few drops of concentrated hydrochloric acid. The cystolithic hairs contain a deposit of calcium carbonate at their base, from which a characteristic effervescence is observed. The heads at the end of the glandular hairs show as a red–purple colour. An alternative method is to add a few drops of chloral hydrate solution to the dry material, which is particularly useful if more detailed information on the structure of the plant tissue is needed, since it removes coloured materials such as chlorophyll. Quantitative analysis and comparison of cannabis, cannabis resin and cannabis oil As already stated, cannabis resin is normally produced in 250 g blocks. Frequently, these blocks carry an impression, such as a number, a letter or a symbol. Comparison can be made between different blocks on the basis of similar impressions, but unrelated blocks frequently have the same impression so caution must be exercised not to assume automatically that similar impressions equals the same source. The street-level deal of cannabis resin is about 3 g (normally in the range 1–10 g), possibly wrapped in tinfoil or plastic. It may be possible to link a smaller piece of cannabis resin to its original block through a physical fit between the smaller and bigger piece. GC or HPLC may be used to obtain a chemical profile of the cannabis, cannabis resin or cannabis oil. The THC content can be calculated and comparison made on that basis. Note that variations can occur in the THC content of a single block of cannabis resin, as the THC content decreases with age and storage conditions. The outside material in a block of cannabis resin can differ from that in the centre, with a lower THC content on the outside. These high lights the need for a careful sampling plan with consideration as to how subsamples should be taken from a larger sample.
