Drug Discovery, Pharmaceuticals & Cannabis Testing
Reproducible Sample Homogenisation of Cannabis and Related Products Dr Tanja Butt, Retsch GmbH,
t.butt@retsch.com
Possession of cannabis was prohibited worldwide in 1925 but today, limited consumption is legal in a growing number of countries, for example Canada, the Czech Republic or Israel. Many countries have started the process of legalising the use of cannabis under strictly regimented conditions for medical treatment, among them Germany.
The concentrations of cannabinoids and terpenoids are the main points of interest in the quality control of cannabis and related products. To ensure reliable analytical results, the sample preparation process for cannabis needs to be adaptable to the considerable complexity of the various plant matrices. There are some challenges to overcome: samples can be sticky (especially in the fl ower buds) and the sample amount may vary greatly. Furthermore, residues leading to sample loss are not acceptable for many testing labs. Retsch offers a range of different laboratory mills to cover the various requirements, including a cutting mill for grinding large sample quantities prior to CBD oil extraction.
Sample homogenisation and small-scale
production of ground cannabis The SM 300 cutting mill is perfect for small scale grinding of dried plant materials such as cannabis (whole plants, fl ower buds, trim leaves), herbs or leaves. The degree of product fi neness can be infl uenced by the speed and by choosing a suitable bottom sieve. Specifi c particle size ranges required for different extraction methods (ethanol, supercritical
CO2) can be obtained. Usually, for cannabis CBD oil extraction processes, particle sizes around
2 mm (extraction with supercritical CO2) or 5-15 mm (extraction with ethanol) particles are required.
Retsch offers a 316L foodGrade version of the SM 300 (Figure 1). All parts in contact with the sample are made of 316L steel, including the long stock hopper, the parallel section rotor and the bottom sieve. For cutting hard and rather compact samples, it is recommended to use the optional 316L rotor with blades made of FDA-certifi ed stainless steel. An optional sample outlet and cyclone unit with 30 l receptacle are also available in 316L steel.
The fold-back hopper of the SM 300 is perfectly suited for easy cleaning, just like the bottom sieves without cassette or edges, where sample material might get trapped. Cleaning of the cyclone and the 30-l receptacle is also quickly done.
Sample homogenisation in the Ultra Centrifugal
Mill ZM 300 The Ultra Centrifugal Mill ZM 300 is the ideal mill for pulverising fi brous samples like hemp plants. It achieves a maximum speed of 23,000 rpm and can be equipped with a large range of accessories, allowing for adaption to the sample´s requirements. Cannabis contains oil which makes it a temperature-sensitive material; to reduce heat build-up during grinding, it is recommended to use a distance sieve. Thanks to a small gap between the sieve and the rotor, the shearing forces and the formation of heat are reduced. 20 g of a pre-cut hemp fl owers can be ground to a particle size smaller than 0.5 mm by using a 0.5 mm distance sieve at a speed of 23,000 rpm (Figure 3). The use of a cyclone has a cooling effect on the sample and helps to effi ciently discharge the material from the grinding chamber. The pulverised sample is now ready for, e. g. extraction of pesticides with the QuEChERS method.
Figure 1. Cutting Mill SM 300 316L foodGrade.
Figure 3. After pre-cutting in the SM 300 (left) the sample is pulverised to <0.5 mm in the ZM 300. Pulverisation of dried cannabis fl owers in the
CryoMill for subsequent pesticide analysis The extraction via QuEChERS can be improved by reducing the particle size to <0.5 mm. Due to the oily and sticky sample properties, the Ultra Centrifugal Mill is not suitable to achieve this. Embrittlement of the sample, e. g. with liquid nitrogen, is a very effective way of making oily materials break easily. Cryogenic grinders like Retsch’s CryoMill or the Mixer Mill MM 500 control are specially designed for these applications, as they continuously cool the grinding jar, and thus the sample, with LN2. The CryoMill produces grind sizes <0.1 mm, which means for the cannabis sample that higher pesticide amounts are detected after extraction than, for example, after grinding in a rotor mill.
Figure 2. Cannabis buds before and after grinding in the SM 300 foodGrade.
In the SM 300 >40 kg/h dried fl ower buds of medical cannabis of approximately 50 mm size can be pulverised at 700 rpm to a fi neness mostly below 2 mm when using a 4 mm bottom sieve (Figure 2). Sample loss is negligible, some dust remains in the grinding chamber and on the sieves or the surfaces of the cyclone and receptacle, usually <0.05%. The low grinding speed ensures good homogenisation results and minimises warming effects.
Application example: 5 g pre-cut cannabis sample are ground in a 50 ml stainless steel grinding jar with one 25 mm stainless steel grinding ball. Sample and ball are fi lled into the jar, the lid is tightly closed, and the jar is clamped into the CryoMill. An automatic pre-cooling function ensures that the grinding process does not start before a temperature of -196°C is reached and maintained. The pre-cooling time is set to 3 min at 5 Hz. Grinding is done at a frequency of 30 Hz for 3 min. Thanks to the autofi ll system of the CryoMill, the user never comes into contact with liquid nitrogen. The embrittled sample can be pulverised to much smaller particle sizes than in the ZM 300 (Figure 4). Still, for larger sample quantities, the ZM 300 is a suitable choice.
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