August 18, 2021
Proper sampling procedures ensure accurate and meaningful analysis of cannabis samples. Most laboratories face challenges in sampling, sample preparation, extraction, and testing procedures. Accuracy in analytical testing begins with unbiased representative sampling and proper sample preparation.
Some samples do not represent the quality of the whole batch. Such samples are termed unrepresentative samples. Unrepresentative sampling leads to sampling errors and can give incorrect or misleading results.
Errors in sampling can lead to biased results and may jeopardize public safety. Representative samples reflect the larger group and represent the characteristics of the group as a whole.
Homogeneity plays an essential role in representative sampling as homogeneous materials are the same throughout the whole. Cannabis plant materials differ in homogeneity levels. It is challenging to collect representative samples from heterogeneous materials.
Concentration gradients in liquid samples may lead to an inhomogeneous distribution of molecules, making sampling of liquids more difficult. Concentration gradients in nonviscous liquids tend to decrease with time more readily compared to viscous liquids. Challenges in liquid inhomogeneity can be overcome by mixing or stirring the sample.
It is difficult to collect representative samples from solids because molecules do not easily diffuse in solid products. Stirring or shaking solids can worsen their homogeneity. One way to homogenize solids is to grind them to produce a fine powder. However, homogenizing solid cannabis plant material using mortar and pestle is not recommended because the material has moisture and is not dry enough to pulverize into a fine powder. An industrial spice grinder may be effective in homogenizing cannabis plant material. The bottom line is that the sample should be as homogenous as possible irrespective of the method chosen for grinding.
Cannabis products are difficult to grind homogeneously due to their physical properties. Even well-trimmed cannabis buds contain stems and leaves that make them heterogeneous. The trim used to make extracts is highly heterogeneous as it contains buds, stems, leaves, seeds, as well as foreign matter. Cannabis plants are fibrous and hence are difficult to cut homogeneously. High amounts of waxes and oils in buds make them stick to the grinding media. Cannabis edibles are also sticky and grinding them is a challenge. All cannabis products vary in moisture content and melting or softening temperature which makes collecting a representative sample even more difficult.
A cannabis flower sample is difficult to grind due to its heterogeneous nature. Simple homogenization techniques use a high-shear grinder that has extremely fast rotating blades. Cannabis flowers can also be broken down into smaller pieces by the sonication technique. A recommended method is to lyophilize or freeze-dry cannabis flowers to remove moisture. Subsequently, it should be placed inside a mechanical ball-bearing homogenizer to pulverize it into a representative sample. The QuEChERS method is often used for solid-phase extraction, which involves dissolving and separating solids for a wide variety of cannabis matrices. This is a quick, easy, and cheap method for dissolving and separating solids.
Cannabis concentrates are not as heterogeneous as cannabis flowers. Here, the sample is prepared by dissolving the concentrate in solvent mixes such as water, acetonitrile, and methanol.
The methods of collecting representative samples vary for different cannabis matrices; however, the objective remains the same. Concentrates, such as shatter and distillate, often lack consistency. However, concentrates are a less complex matrix compared to flowers. The sample batch is heated and stirred to achieve a homogenous and uniform sample if concentrates are in a distillate or oil form. Shatter is a solid material that tends to lose consistency when heated or immersed into a solvent. For collecting a representative sample, a technician can use a spatula to collect samples from different areas of shatter.
Laboratories are required to follow strict regulatory guidelines to manage every gram of each sample from testing to disposal. A laboratory information management system (LIMS) can help cannabis testing laboratories maintain a chronological record of custodians right from sample collection, transportation to the testing laboratory, sample accessioning, preparation and analysis, to disposal. It also supports sample traceability through barcodes or tags to meet the requirements of state and local laws. A Cannabis LIMS generates personalized Certificates of Analysis (CoA) containing sampling details, sample information, test details, and test results as per the requirements of ISO 17025 compliance. Furthermore, a LIMS eliminates chances of transcription errors and data redundancy and assures data integrity.
Representative sampling and proper sample preparation are the two most common necessities of accurate sample analysis. Proper sampling is crucial for cannabis testing laboratories. Cannabis testing laboratories find it challenging to collect representative samples from complex heterogeneous cannabis matrices. Cannabis testing laboratories must ensure to prepare and collect a homogeneous sample before analysis in order to get reproducible and valid results. A laboratory information management system (LIMS) enables cannabis testing laboratories to easily manage sampling data, samples, tests, and multi-analyte test results. It traces samples as they are grouped in batches, tested, and stored. Furthermore, a Cannabis LIMS maintains a complete chain-of-custody from sample collection, handling, analysis to disposal. Hence, cannabis testing laboratories should deploy a LIMS to streamline workflows and enhance productivity.