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Cannabis Analysis: Pesticides, Potency, and Elements

July 16, 2018

Since 1970, marijuana has been designated a Schedule 1 drug under the Controlled Substances Act, making it nearly impossible for academic labs to perform cannabis research. However, medicinal use of cannabis is now legal in Canada, 29 US states, the Czech Republic and Israel. With the law under review, the UK is currently licensing cannabis oil on a case-by-case basis, with the first license granted in June 2018. All of this interest in medical cannabis has highlighted the need for good analysis methodology in this relatively young market. Cannabis analysis is still developing standardized protocols, requirements, and acceptable testing practices. Typical testing requirements for cannabis and its products include heavy metal analysis, pesticide residue, and the potency of active ingredients such as tetrahydrocannabinol (THC). The terpene content of cannabis is also important. Terpenes have been shown to have beneficial uses for treatment of conditions ranging from cancer and inflammation to anxiety and sleeplessness. It is believed that the combination of terpenes and cannabinoids in cannabis produce a synergistic effect with regards to medical benefits.

The Challenges

Physically handling dry cannabis materials requires care especially for trace level contaminant analysis, such as pesticide residue testing. Since cannabis is a cultivated plant, there are some innate health and safety risks and analysis can answer some important questions. Was it treated with pesticides? Was it grown properly to prevent the formation of mold (mycotoxins)? How was it stored and handled? Sample preparation is critical to obtaining good data, as a complex material such as cannabis has a high potential for matrix interference.

Products

There is now a huge variety of cannabis-based products – such as THC-infused chocolate, concentrates, beverages, perfumes and foot creams. These have provided some unique issues in cannabis analysis. These various sample forms require different sample preparation techniques and this can create inter-sample variability and inconsistency when comparing results. The advice is to work with proven sample preparation technologies. It is essential to develop a standard methodology for sample preparation to provide consistency in the analysis. Matrix effects and sample preparation can complicate testing. For example, when testing an edible sample, the tetrahydrocannabinol levels may not be uniform across the product, so representative sampling is imperative.

Potency

The most common cannabis analysis conducted on flowers, concentrates and infused products is potency testing to determine the percentage of cannabinoids such as THC, THCA, CBD. The high percent level of THC and other cannabinoids that have been bred into the plant makes sample preparation even more challenging. There are literally dozens of different cannabinoids each with a different activity. Eight of these are of the most interest in potency testing and provide a bench-mark for commercial cannabis. The primary objective is typically the quantification of the tetrahydrocannabinol/cannabidiol (THC/CBD) ratio. THC is psychoactive, but CBD isn’t, and for medical marijuana, a higher ratio of the latter is often preferred. Hemp is a strain of cannabis that is bred to diminish the amount of THC to 0.4% or below. This variety is favored for its fibers and is commonly used for clothing and other nonmedicinal purposes. Overall it is vital for medical users to realize how strong the cannabis is and to appreciate the relative amounts of cannabinoids.

Current Sample Preparation

The QuEChERS method, which is based upon solid phase extraction is practical for pesticide, cannabis actives, mycotoxins and terpene analysis and is increasingly being employed on more difficult plant matrices such as cannabis. The problem is this process is a time consuming manual multi-step process. Headspace solid-phase microextraction (HS-SPME) has been used to identify and quantify terpene content in cannabis. The HS-SPME method is superior to solvent extraction as it provides a cleaner analysis, has no interferences from coextracted matrix, and is non-destructive to the sample.

Energized Dispersive Guided Extraction (EDGE)

EDGE™ is an alternative to QuEChERS in the extraction of compounds from difficult matrices. EDGE™ is a sequential system for the fast-automated solvent extraction of up to 12 samples. The method can extract a difficult sample, including the dispersive solid phase clean up, in one automated step. With EDGE, the sample and sorbents are together in one sample cell allowing extraction and clean-up in one step. In under 5 minutes, the sample can be extracted using Q-Cup Technology which performs both extraction and clean-up of the sample. The collected extract is then filtered, cooled and ready for analysis. EDGE™ offers the fastest pesticide, terpene, cannabinol or mycotoxin extraction possible in one simple method. EDGE™ is rapid, inexpensive and convenient.

Q-Cup Technology

Q-Cup Technology combines the process of Pressurised Fluid Extraction and Dispersive Solid Phase Extraction in a single instrument for rapid and efficient extraction. This allows different samples to be quickly extracted. Extractions in the EDGE™ are carried out under pressure and at elevated temperatures, which speeds up the reaction kinetics. In addition to this quicker desorption of the analytes from the matrix, heating and cooling of the sample is carried out by a special process in a few seconds. Accelerated solvent extraction with EDGE is faster than Soxhlet, ultrasound, classical ASE, QuEChERS or other conventional extraction methods and requires much less solvent while at the same time requiring considerably less effort. The extraction cell Q-Cup, with a unique open cell concept, contains a porous Q-Disk on the bottom. The sample to be examined is loaded into this Q-Cup and the Q-Cup is into the autosampler. The gripper arm transports the Q-Cup into the sample chamber and then the Q-Cup is automatically pressure-tight sealed. After addition of the solvent, the cell is heated to a maximum of 180°C with elevated pressure and kept under constant conditions for two minutes to disperse the analytes out of the sample. The solvent extract is automatically filtered by the Q-Cup Disc, cooled down and transferred into the collection vial.

The Analysis

Pesticide residue analysis of cannabis plant material is accomplished by using sensitive and selective detection such as GC and LC MS/MS. GC and LC are both needed because some pesticides are only reproducibly detected at low enough levels by one or the other. Although many pesticides can be detected by both. Trace pesticide analysis requires high selectivity and MS/MS is used to counter the complex matrix. The sample preparation and clean-up of EDGE is essential to minimize ion suppression. Mycotoxins analysis is challenging because of the low detection limits required, and affinity-based sample preparation with HPLC or LC-MS/MS is most often used. The majority of analyses are potency tests and these are usually conducted with UHPLC. UHPLC is preferred over GC, as the cannabinoids are mainly present in their acidic form in the plant material.

Trace Metals Analysis

Certain heavy metals can cause adverse effects on human health. Toxic heavy metals such as arsenic, cadmium, lead, and mercury are persistent once released into the environment and can accumulate in Cannabis plants. Cannabis-based products such as foods, oils, tinctures and salves should be tested for the presence of heavy metals to ensure patient safety and product quality.

The MARS 6 for Elemental Analysis

The MARS 6 microwave digestion system is the choice for sample preparation of cannabis in trace elemental analysis. The MARS 6 uses integrated sensor technology to recognize the vessel and the sample number and uses that to create a custom algorithm to ensure a custom digestion process. There are options for remote system control and contactless all vessel temperature control. The MARS 6 is a batch acid digestion microwave system. It can heat up to 40 samples during the same run. Microwave is a technique used to dissolve solid sample matrices into an aqueous liquid. This is achieved by placing a sample in a concentrated acid matrix in a closed vessel and exposing it to microwave irradiation. The speed of thermal decomposition of the sample, and the solubility of metals are both increased. Once these metals are in solution, they can be analyzed quantitatively and qualitatively using spectroscopic techniques. The MARS 6 acid digestion process routinely cuts the time of sample preparation by 50 – 75 % compared to hot plates.

Cannabis

The marketing and regulation of cannabis as a legal medical product is set to bring new challenges. The product must adhere to the highest levels of safety. There are likely to be stricter regulations in the future, which will result in a safer product. This will depend upon good analytical methodology. The use of EDGE and the MARS microwave system in the preparation of cannabis samples for analysis will provide a good basis for the preparation of consistent samples for analysis.

References

  1. “Medical use of marijuana”, N Engl J Med, 368, 866–868 (2013).
  2. I Grant et al, “Medical marijuana: clearing away the smoke”, Open Neurol J 2012;6:18-25.
  3. A Hazekamp et al, “The medicinal use of cannabis and cannabinoids – an international cross-sectional survey on administration forms”, J Psychoactive Drugs, 45 (3), 199–210 (2013).
Disclaimer.
Possessing, using, distributing or selling marijuana or marijuana-based products constitute federal crimes in the United States, even where a state law decriminalizes or legalizes such activities. CEM Corporation produces instruments that are intended for use in testing laboratories and applications only where such use is permitted under applicable state/country law.