5.1 The sample preparation procedure for comminution impacts other downstream processes such as extraction and sonication, which ultimately affects the total analytical error (TAE) and measurement uncertainty.

5.2 Factors that may influence the sample preparation process include the prevention of cross-contamination (carryover) from a prior sample and an inadequate cleaning procedure between preparation of samples, poor sample handling, storage (sample preservation), and moisture content (drying methods) of plant material being greater than 15?% (15). Samples with high moisture content are hard to process completely and may yield lower analyte (that is, cannabinoid) concentration during extraction and further processing. Lastly, water activity Specification D8197 is recommended, activity (aw) range (0.55 to 0.65) for dry cannabis or hemp flower or both.

5.3 There are many different types of hardware technologies that address the comminution of dried cannabis or hemp; however, the list of devices is exhaustive and thus beyond the scope of this guide. See Table 3 and Table 4 (16-18) for a summary of different milling technologies. Distinctions among various pieces of equipment often relate to the type, mass, and size/shape of the sample (dry, fibrous) for which each is most effective. In addition, there may be economic reasons for mill selection, that is, the sample throughput of the testing laboratory (number of samples per day), access to cryogenics, and sample mass requirements.

5.4 In addition to sampling devices, this guide does not include the sample preparation of edibles, tinctures, oils/concentrates, beverages, and so forth in which the sample diversity poses significant sample preparation challenges to be put forward in additional work items.

5.5 The sample size for comminution purposes is limited as the analytical testing portion required is often 500 times smaller than the bulk sample lot and not every testing laboratory is equipped to handle large sample sizes (that is, greater than 100?g of dried cannabis inflorescence/hemp).

5.6 The particle size is determined by passing the milled cannabis/hemp material through standard sieves, for example, starting with #18 (1000?μm) for the optimum particle size is further determined by extraction efficiency, where <1?mm for cannabis and hemp has been previously reported.

5.7 Preparing multiple analytical samples from one comminuted primary sample and their parallel analysis gives information about the repeatability of the corresponding analytical process (including sample preparation, injection, and integration) and reflects on the homogeneity of the primary sample.

5.8 Moisture removal is critical before any comminution. This step can be accomplished by "drying" at various temperatures ranging from freeze drying to ambient room temperature, as well as vacuum oven drying and forced air oven drying. Some of the active compounds in the product are temperature sensitive, and thus, freeze drying before primary and secondary drying steps is expected to be advantageous in reducing quality deterioration.

5.9 Freeze drying is often a fast approach when a vacuum holds the cannabis plant at temperatures below -40?°C, which retains the high-quality phytochemicals, for example, volatile compounds (terpenes/terpenoids) and acidic forms of cannabinoids. In addition, embrittlement is accomplished before comminution by freezing (-80?°C freezer, for example) for a set time period or by adding cryogen dry ice or liquid gases, such as liquid nitrogen.

5.10 Cryogenic milling may be the preferred way of particle size reduction because of the fact that cannabis/hemp inflorescence exhibits many material properties that can be challenging (that is, moisture content, oil/resin content, and fibrosity). In cannabis milling applications, it is common to add liquid nitrogen directly into the mill to reduce the heat of grinding. Another step may include placing the sample into a liquid bath or immersion sample assembly that pre-cools the material in advance of feeding the material into the cryogenic mill. If available, cryogenic cooling of hemp and cannabis inflorescence samples before and during the grinding process can be an efficient way to prevent thermal degradation during grinding. Lower temperatures may achieve:

5.10.1 Induces microscopic fractures in hemp/cannabis inflorescence before grinding, reducing the energy required to grind it.

5.10.2 Makes the plant material brittle, which is easier to grind mechanically.

5.10.3 It can lower the heat capacity (the amount of heat supplied to a given mass of material to generate a change of unit temperature) and decrease the amount of energy needed to change the temperature of the hemp/cannabis inflorescence, which increases the efficiency of grinding. Depending on the material of the cutting zone, the lowest cutting capability may be achieved with LCO₂ followed by LN₂ correlated to the material feed flow rate.