Sample Preparation in Cannabis Testing Labs

November 17, 2021

Sample preparation is an important factor for both sampling agents and the testing lab to make sure that the sample is a good representation of the lot and the results reflect an accurate cannabinoid detection. This article aims to clarify for both sides what makes a sample representative and how the labs can ensure a comprehensive analysis.

WHAT MAKES A SAMPLE REPRESENTATIVE?

A representative sample is a selected few from a population that seeks to represent and reflect the characteristics of the larger population.(1) While mainly used for statistical analysis in marketing and psychological studies with people (see figure 1), a representative sample is also very important in the agricultural and scientific field for hemp sampling agents to make sure the whole lot of crop is growing similarly in the field. For a representative sample, sampling agents take clippings from various plants among the lot and combine them in a sample bag to send to a lab for analysis. This composite sample is then further processed and homogenized by the lab to make sure the results are also a good representation of the sample and, therefore, the whole lot.

Figure 1. A visual representation of selecting a representative sample.

In order to create a sample that is representative of the lot/crop, be sure to consult your local department of agriculture or following the United States Department of Agriculture on how to take samples for official analysis. For example, the Texas Department of Agriculture (TDA) has guidelines about when and where to take samples. The TDA requires a certain number of clippings to be collected depending on the size of the lot in acres, with the most common sample number being 5 clippings. The TDA also requires the sample to be taken from a specified location on the plant, that being “underneath a flowering material [...] located at the top one-third of the plant.” (2) Once the clippings are collected, they are placed in the sample collection bag and sent to the testing laboratory with the relevant official paperwork needed for analysis.

HOW DO TESTING LABS PROVIDE REPRESENTATIVE DATA?

Once the sample is received by the lab, further preparation is taken before the sample is used for analysis. This can include drying the sample to the appropriate moisture content (4), separating seeds from the sample, and even further homogenization.

Here at Ionization Labs, our sample preparation includes further homogenization to ensure that the representative sample is evenly mixed before analysis. Since the plant material is heterogeneous, or a mixture of different parts (i.e. stems, leaves, buds, etc.), the various parts of the plant can vary in cannabinoid content. Grinding the entire plant material ensures an even mixture of the various parts for analysis with minimal leaching from the plant as shown below (figure 2). Once the plant material is ground up in an even mixture, a sample is taken from the grounds as a representative sample of the whole for laboratory analysis. If done carefully and properly, this even mixture of plant material can be assumed to be a good representation of the lot for accurate cannabinoid analysis.