Tag Archives: liquid chromatography

An Evaluation of Sample Preparation Techniques for Cannabis Potency Analysis

By Kelsey Cagle, Frank L. Dorman, Jessica Westland
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Sample preparation is an essential part of method development and is critical to successful analytical determinations. With cannabis and cannabis products, the analyst is faced with a very challenging matrix and targets that may range from trace level through percent level thus placing considerable demands on the sample preparation techniques.1 The optimal sample preparation, or “extraction”, method for potency analysis of cannabis flower was determined using a methanol extraction coupled with filtration using regenerated cellulose filters. 

In the United States (US), Canada, and other countries where medicinal and/or adult recreational cannabis has been legalized, regulatory entities require a panel of chemical tests to ensure quality and safety of the products prior to retail sales2. Cannabis testing can be divided into two different categories: Quality and Safety. Quality testing, which includes potency analysis (also known as cannabinoid testing or cannabinoid content), is performed to analyze the product in accordance with the producer/grower expectations and government regulations. Safety testing is conducted under regulatory guidelines to ensure that consumers are not exposed to toxicants such as pesticides, mycotoxins, heavy metals, residual solvents and microbial contaminates.

Potency testing evaluates the total amount of cannabinoid content, specifically focusing on tetrahydrocannabinol (THC) and cannabidiol (CBD). In the US, the biggest push for accurate total THC is to differentiate between hemp (legally grown for industrial or medicinal use), which is defined as cannabis sativa with a THC limit ≤ 0.3 %, and cannabis (Cannabis spp.), which is any cannabis plant with THC measured above 0.3 %3. Potency testing is typically performed by liquid chromatography (LC) with UV detection to determine the quantity of major cannabinoids.

In addition to reporting THC and CBD, their respective precursors are also important for reporting total potency. Tetrahydrocannabinolic acid (THCA) is the inactive precursor to THC while cannabidiolic acid (CBDA) is the precursor to CBD.4,5

Methods and Materials

Sample Preparation

All samples were homogenized using an immersion blender with a dry material grinder. The nominal sample amounts were 200 mg of flower, 500 mg of edibles, and 250 mg of candy samples.

Potency Extraction Method (1)

Twenty milliliters (mL) of methanol (MeOH) was added to each sample. The samples were mechanically shaken for 10 minutes and centrifuged for 5 minutes.

Potency Extraction Method (2)

Ten mL of water was added to each sample. The samples were mechanically shaken for 10 minutes. 20 mL of acetonitrile (ACN) was then added to each sample and vortexed. An EN QuEChERS extraction salt packet was added to the sample. The samples were placed on a mechanical shaker for 2 minutes and then centrifuged for 5 minutes.

Each extract was split and evaluated with two filtration/cleanup steps: (1) a regenerated cellulose (RC) syringe filter (Agilent Technologies, 4 mm, 0.45 µm); (2) a PFTE syringe filter (Agilent Technologies, 4 mm, 0.45 µm). The final filtered extracts were injected into the ultra-performance liquid chromatograph coupled with a photodiode array detector (UPLC-PDA) for analysis.

Figure 1: Calibration curve for THC potency

Calibration

Standards were obtained for the following cannabinoids at a concentration of 1 mg/mL: cannabidivarin (CBDV), tetrahydrocannabivarin (THCV), cannabidiol (CBD), cannabigerol (CBG), cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), cannabinol (CBN), tetrahydrocannabinol (9-THC), cannabichromene (CBC), tetrahydrocannabinol acid (THCA). Equal volumes of each standard were mixed with MeOH to make a standard stock solution of 10 ug/mL. Serial dilutions were made from the stock to make concentrations of 5, 1, and 0.5 ug/mL for the calibration curve (Figure 1).

Instrumental Method

All instrument parameters were followed from Agilent Application Note 5991-9285EN.8 A UPLC with a PDA (Waters Corp, Milford, MA) detector was employed for potency analysis. An InfinityLab Poroshell 120 EC-C18, 3.0 x 50 mm, 2.7 um column (Agilent Technologies, Wilmington, DE) was utilized for compound separation. The organic mobile phase composition was 0.05 % (v/v) formic acid in HPLC grade MeOH and the aqueous mobile phase composition was 0.1 % (v/v) formic acid in HPLC grade water. The mobile phase gradient is shown in Table 1. The flow rate was 1 mL/min (9.5 minute total program), injection volume was 5 uL, and column temperature was 50 °C.

Table 1: LC mobile phase gradient for potency samples6

Discussion and Results

Table 2 summarizes the relative standard deviations (% RSD) were found for the THC calibrator (at 1 ug/mL) and one extract of a homogeneous sample (utilizing 7 replicates).

Table 2- %RSD values for the instrument response precision for THC in both the calibrations and the homogeneous extract.

The cannabinoid potency of various cannabis plant and cannabis product samples were determined for the various extraction techniques In the chromatograms THC was observed ~8.08 minutes and CBD was observed ~4.61 minutes (Figure 2).

Figure 2: Chromatogram of the 10ug/mL calibrator for potency/cannabinoid analysis

Total potency for THC & CBD were calculated for each sample using the equations below. Equation 1 was used because it accounts for the presence of THCA as well as the specific weight difference between THC and THCA (since THCA will eventually convert to THC, this needs to be accounted for in the calculations).

Table 3 shows the % THC and the total THC potency values calculated for the same flower samples that went through all four various potency sample preparation techniques as described earlier. Figure 3 also provides LC chromatograms for flower sample 03281913A-2 and edible sample 03281912-1.

Table 3-THC and Total THC potency values for the same cannabis flower sample processed through the combination of extractions and cleanups.
Figure 3: Potency/Cannabinoid analysis chromatogram for flower sample 03281913A-2 (red trace) and edible sample 03281912-1 (green trace).

The results indicated that with the “Potency Extraction Method 2” (ACN/QuEChERS extraction) coupled with the RC filter provided a bias of 7.29 % greater for total THC % over the other extraction techniques. Since the other 3 techniques provided total THC values within 2% of each other, the total THC of the sample is more likely ~14%.

Since the sample dilution for the above data set reduced the CBD content, an undiluted sample was run and analyzed. This data is reported in Table 4.

Table 4- CBD and Total CBD potency values for the same cannabis flower sample processed through different sample preparation techniques.

The CBD results indicated that with the “Potency Extraction Method 1” (methanol extraction) coupled with RC filter, allowed for a greater CBD recovery. This may indicate the loss of CBD with an ACN/QuEChERS extraction.

With an average ~14% total THC and 0.06% total CBD for a homogenous cannabis flower sample, the optimal sample preparation extraction was determined to be a methanol extraction coupled with filtration using a regenerated cellulose filter. Since potency continues to remain at the forefront of cannabis regulatory testing it is important to utilize the right sample prep for your cannabis samples.

References

  1. Wang M, Wang YH, Avula B, Radwan MM, Wanas AS, Mehmedic Z, et al. Quantitative Determination of Cannabinoids in Cannabis and Cannabis Products Using Ultra-High-Performance Supercritical Fluid Chromatography and Diode Array/Mass Spectrometric Detection. Journal of Forensic Sciences 2016;62(3):602-11.
  2. Matthew Curtis, Eric Fausett, Wendi A. Hale, Ron Honnold, Jessica Westland, Peter J. Stone, Jeffery S. Hollis, Anthony Macherone. Cannabis Science and Technology, September/October 2019, Volume 2, Issue 5.
  3. Sian Ferguson. https://www.healthline.com/health/hemp-vs-marijuana. August 27, 2020.
  4. Taschwer M, Schmid MG. Determination of the relative percentage distribution of THCA and 9-THC in herbal cannabis seized in Austria- Impact of different storage temperatures on stability. Forensic Science International 2015; 254:167-71.
  5. Beadle A. CBDA Vs CBD: What are the differences? [Internet]. Analytical Cannabis. 2019 [cited 2020 Apr 22]; https://www.analyticalcannabis.com/articles/cbda-vs-cbd-what-are-the-differences-312019.
  6. Storm C, Zumwalt M, Macherone A. Dedicated Cannabinoid Potency Testing Using the Agilent 1220 Infinity II LC System. Agilent Technologies, Inc. Application Note 5991-9285EN
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The Four Pillars of Cannabis Processing

By Christian Sweeney
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extractiongraphic

Cannabis extraction has been used as a broad term for what can best be described as cannabis processing. A well-thought-out cannabis process goes far beyond just extraction, largely overlapping with cultivation on the front-end and product development on the back-end1. With this in mind, four pillars emerge as crucial capabilities for developing a cannabis process: Cultivation, Extraction, Analytics and Biochemistry.

The purpose and value of each pillar on their own is clear, but it is only when combined that each pillar can be optimized to provide their full capacities in a well-designed process. As such, it is best to define the goals of each pillar alone, and then explain how they synergize with each other.

At the intersection of each pillar, specific technology platforms exist that can effectively drive an innovation and discovery cycle towards the development of ideal products.Cultivation is the foundation of any horticultural process, including cannabis production. Whether the goal be to convert pigments, flavors or bioactive compounds into a usable form, a natural process should only utilize what is provided by the raw material, in this case cannabis flower. That means cultivation offers a molecular feedstock for our process, and depending on our end goals there are many requirements we may consider. These requirements start as simply as mass yield. Various metrics that can be used here include mass yield per square foot or per light. Taken further, this yield may be expressed based not only on mass, but the cannabinoid content of the plants grown. This could give rise to a metric like CBD or THC yield per square foot and may be more representative of a successful grow. Furthermore, as scientists work to learn more about how individual cannabinoids and their combinations interact with the human body, cultivators will prioritize identifying cultivars that provide unique ratios of cannabinoids and other bioactive compounds consistently. Research into the synergistic effect of terpenes with cannabinoids suggests that terpene content should be another goal of cultivation2. Finally, and most importantly, it is crucial that cultivation provide clean and safe materials downstream. This means cannabis flower free of pesticides, microbial growth, heavy metals and other contaminants.

Extraction is best described as the conversion of target molecules in cannabis raw material to a usable form. Which molecules those are depends on the goals of your product. This ranges from an extract containing only a pure, isolated cannabinoid like CBD, to an extract containing more than 100 cannabinoids and terpenes in a predictable ratio. There are countless approaches to take in terms of equipment and process optimization in this space so it is paramount to identify which is the best fit for the end-product1. While each extraction process has unique pros and cons, the tunability of supercritical carbon dioxide provides a flexibility in extraction capabilities unlike any other method. This allows the operator to use a single extractor to create extracts that meet the needs of various product applications.

Analytics provide a feedback loop at every stage of cannabis production. Analytics may include gas chromatography methods for terpene content3 or liquid chromatography methods for cannabinoids 3, 4, 5. Analytical methods should be specific, precise and accurate. In an ideal world, they can identify the compounds and their concentrations in a cannabis product. Analytics are a pillar of their own due simply to the efforts required to ensure the quality and reliability of results provided as well as ongoing optimization of methods to provide more sensitive and useful results. That said, analytics are only truly harnessed when paired with the other three pillars.

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Figure 1: When harnessed together the pillars of cannabis processing provide platforms of research and investigation that drive the development of world class products.

Biochemistry can be split into two primary focuses. Plant biochemistry focuses back towards cultivation and enables a cannabis scientist to understand the complicated pathways that give rise to unique ratios of bioactive molecules in the plant. Human biochemistry centers on how those bioactive molecules interact with the human endocannabinoid system, as well as how different routes of administration may affect the pharmacokinetic delivery of those active molecules.

Each of the pillars require technical expertise and resources to build, but once established they can be a source of constant innovation. Fig. 1 above shows how each of these pillars are connected. At the intersection of each pillar, specific technology platforms exist that can effectively drive an innovation and discovery cycle towards the development of ideal products.

For example, at the intersection of analytics and cultivation I can develop raw material specifications. This sorely needed quality measure could ensure consistencies in things like cannabinoid content and terpene profiles, more critically they can ensure that the raw material to be processed is free of contamination. Additionally, analytics can provide feedback as I adjust variables in my extraction process resulting in optimized methods. Without analytics I am forced to use very rudimentary methods, such as mass yield, to monitor my process. Mass alone tells me how much crude oil is extracted, but says nothing about the purity or efficiency of my extraction process. By applying plant biochemistry to my cultivation through the use of analytics I could start hunting for specific phenotypes within cultivars that provide elevated levels of specific cannabinoids like CBC or THCV. Taken further, technologies like tissue culturing could rapidly iterate this hunting process6. Certainly, one of the most compelling aspects of cannabinoid therapeutics is the ability to harness the unique polypharmacology of various cannabis cultivars where multiple bioactive compounds are acting on multiple targets7. To eschew the more traditional “silver bullet” pharmaceutical approach a firm understanding of both human and plant biochemistry tied directly to well characterized and consistently processed extracts is required. When all of these pillars are joined effectively we can fully characterize our unique cannabis raw material with targeted cannabinoid and terpene ratios, optimize an extraction process to ensure no loss of desirable bioactive compounds, compare our extracted product back to its source and ensure we are delivering a safe, consistent, “nature identical” extract to use in products with predictable efficacies.

Using these tools, we can confidently set about the task of processing safe, reliable and well characterized cannabis extracts for the development of world class products.

[1] Sweeney, C. “Goal-Oriented Extraction Processes.” Cannabis Science and Technology, vol 1, 2018, pp 54-57.

[2] Russo, E. B. “Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects.” British Journal of Pharmacology, vol. 163, no. 7, 2011, pp. 1344–1364.

[3] Giese, Matthew W., et al. “Method for the Analysis of Cannabinoids and Terpenes in Cannabis.” Journal of AOAC International, vol. 98, no. 6, 2015, pp. 1503–1522.

[4] Gul W., et al. “Determination of 11 Cannabinoids in Biomass and Extracts of Different Varieties of Cannabis Using high-Performance Liquid Chromatography.” Journal of AOAC International, vol. 98, 2015, pp. 1523-1528.

[5] Mudge, E. M., et al. “Leaner and Greener Analysis of Cannabinoids.” Analytical and Bioanalytical Chemistry, vol. 409, 2017, pp. 3153-3163.

[6] Biros, A. G., Jones, H. “Applications for Tissue Culture in Cannabis Growing: Part 1.” Cannabis Industry Journal, 13 Apr. 2017, www.cannabisindustryjournal.com/feature_article/applications-for-tissue-culture-in-cannabis-growing-part-1/.

[7] Brodie, James S., et al. “Polypharmacology Shakes Hands with Complex Aetiopathology.” Trends in Pharmacological Sciences, vol. 36, no. 12, 2015, pp. 802–821.