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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

A More Effective and Efficient Approach to Purer Cannabidiol Production Using Centrifugal Partition Chromatography

By Lauren Pahnke
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Many physicians today treat their patients with cannabidiol (CBD, Figure 1), a cannabinoid found in cannabis. CBD is more efficacious over traditional medications, and unlike delta-9 tetrahydrocannbinol (THC), the main psychoactive compound in cannabis, CBD has no psychoactive effects. Researchers have found CBD to be an effective treatment for conditions such as cancer pain, spasticity in multiple sclerosis, and Dravet Syndrome, a form of epilepsy.

CBD is still considered an unsafe drug under federal law, but to meet the medical demand, 17 states in the US recently passed laws allowing individuals to consume CBD for medical purposes. A recent survey found that half of medicinal CBD users rely on the substance by itself for treatment. As doctors start using CBD to treat more patients, the demand for CBD is only expected to rise, and meeting that demand can pose challenges for manufacturers who are not used to producing such high quantities of CBD. Furthermore, as CBD-based drugs become more popular, the US Food and Drug Administration (FDA) will likely require manufacturers to demonstrate they can produce pure, high-quality products.

cannabidiol
Figure 1. The structure of cannabidiol, one of 400 active compounds found in cannabis.

Most manufacturers use chromatography techniques such as high performance liquid chromatography (HPLC) or flash chromatography to isolate compounds from natural product extracts. While these methods are effective for other applications, they are not, however, ideal for CBD isolate production. Crude cannabis oil contains some 400 potentially active compounds and requires pre-treatment prior to traditional chromatography purification. Both HPLC and flash chromatography also require silica resin, an expensive consumable that must be replaced once it is contaminated due to irreversible absorption of compounds from the cannabis extract. All of these factors limit the production capacity for CBD manufacturers.

Additionally, these chromatography methods use large quantities of solvents to elute natural compounds, which negatively impacts the environment.

A Superior Chromatography Method

Centrifugal partition chromatography (CPC) is an alternative chromatography method that can help commercial CBD manufacturers produce greater quantities of pure CBD more quickly and cleanly, using fewer materials and generating less toxic waste. CPC is a highly scalable CBD production process that is environmentally and economically sustainable.

The mechanics of a CPC run are analogous to the mechanics of a standard elution using a traditional chromatography column. While HPLC, for instance, involves eluting cannabis oil through a resin-packed chromatography column, CPC instead elutes the oil through a series of cells embedded into a stack of rotating disks. These cells contain a liquid stationary phase composed of a commonly used fluid such as water, methanol, or heptane, which is held in place by a centrifugal force. A liquid mobile phase migrates from cell to cell as the stacked disks spin. Compounds with greater affinity to the mobile phase are not retained by the stationary phase and pass through the column faster, whereas compounds with a greater affinity to the stationary phase are retained and pass through the column slower, thereby distributing themselves in separate cells (Figure 2).

Figure 2- CPC
Figure 2. How CPC isolates compounds from complex, natural mixtures. As the column spins, the mobile phase (yellow) moves through each cell in series. The compounds in the mobile phase (A, B, and C) diffuse into the stationary phase (blue) at different rates according to their relative affinities for the two phases.

A chemist can choose a biphasic solvent system that will optimize the separation of a target compound such as CBD to extract relatively pure CBD from a cannabis extract in one step. In one small-scale study, researchers injected five grams of crude cannabis oil low in CBD content into a CPC system and obtained 205 milligrams of over 95% pure CBD in 10 minutes.

Using a liquid stationary phase instead of silica imbues CPC with several time and cost benefits. Because natural products such as raw cannabis extract adhere to silica, traditional chromatography columns must be replaced every few weeks. On the other hand, a chemist can simply rinse out the columns in CPC and reuse them. Also, unlike silica columns, liquid solvents such as heptane used in CPC methods can be distilled with a rotary evaporator and recycled, reducing costs.

Environmental Advantages of CPC

The solvents used in chromatography, such as methanol and acetonitrile, are toxic to both humans and the environment. Many environmentally-conscious companies have attempted to replace these toxic solvents with greener alternatives, but these may come with drawbacks. The standard, toxic solvents are so common because they are integral for optimizing purity. Replacing a solvent with an alternative could, therefore, diminish purity and yield. Consequently, a chemist may need to perform additional steps to achieve the same quality and quantity achievable with a toxic solvent. This produces more waste, offsetting the original intent of using the green solvent.

CPC uses the same solvents as traditional chromatography, but it uses them in smaller quantities. Furthermore, as previously mentioned, these solvents can be reused. Hence, the method is effective, more environmentally-friendly, andeconomically feasible.

CPC’s Value in CBD Production

As manufacturers seek to produce larger quantities of pure CBD to meet the demand of patients and physicians, they will need to integrate CPC into their purification workflows. Since CPC produces a relativelyduct on a larger scale, it is equipped to handle the high-volume needs of a large manufacturer. Additionally, because it extracts more CBD from a given volume of raw cannabis extract, and does not use costly silica or require multiple replacement columns, CPC also makes the process of industrial-scale CBD production economically sustainable. Since it also uses significantly less solvent than traditional chromatography, CPC makes it financially feasible to make the process of producing CBD more environmentally-friendly.

Suggested Reading:

CPC 250: Purification of Cannabidiol from Cannabis sativa

Introduction to Centrifugal Partition Chromatography