Analyzing Pesticide Residue of Cannabis

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In 1970, marijuana was designated a Schedule 1 drug as part of the Controlled Substances Act. This made it almost impossible for academic labs to carry out cannabis research. Today however, the medicinal use of cannabis is legal in 29 US states, Canada, Israel and the Czech Republic. In the UK, the law is currently under review, and cannabis oil is currently being licensed on a case-by-case basis since the first license was granted in June 2018.

In a relatively young market, with significant interest in medical cannabis, a requirement for good analysis methodology has been highlighted. Standard protocols, requirements, and testing practices are still being developed for use in cannabis analysis, with typical tests including those for active ingredients, such as tetrahydrocannabinol (THC) and their potency, as well for pesticide residues and heavy metals.

Another important factor is the terpene content of cannabis. Terpenes have been shown to have beneficial uses for the treatment of a range of conditions, from anxiety and insomnia, to inflammation and cancer, and it is believed that in combination with cannabinoids, terpenes can produce a synergistic effect with medical benefits. It is believed that the combination of terpenes and cannabinoids in cannabis produce a synergistic effect with regards to medical benefits.

Challenges

For trace level analysis of contaminants, for example in pesticide residue testing, care must be taken when physically handling dry cannabis materials. As cannabis is a cultivated plant, some health and safety risks are innate, and analysis can answer some important questions. [How was it stored and handled? Were pesticides used during growth? Was growth carried out properly, avoiding the formation of mold (mycotoxins)?]. The preparation of samples is crucial in order to obtain good data, as complex materials like cannabis have a high potential for matrix interference.

Product Variety

A large variety of cannabis-based products are now available, including THC-infused beverages, chocolates, concentrates, foot creams and perfumes, each present unique issues in cannabis analysis. For different types of samples, different preparation techniques must be used, and this can lead to inter-sample variability and inconsistency when comparing results. As such, it is generally advised to work with proven sample preparation technologies, while a standard methodology must be developed to achieve consistency in the analysis.

Testing can be further complicated by sample preparation methods or Matrix effects. In an edible sample, for example, the distribution of active ingredients, such as tetrahydrocannabinol can be non-uniform across the product making representative sample necessary.

Potency

Potency testing is the most common analysis carried out on flowers, concentrates and infused products. This is used to calculate the percentage of various cannabinoids (THC, THCA and CBD). Sample preparation is made more difficult by the high percent level of THC and other cannabinoids present in the plant, with literally dozens of different cannabinoids each with a different activity.

Eight of these are of the most interest in potency testing and are used to provide a bench-mark for commercial cannabis, typically via the quantification of the tetrahydrocannabinol/cannabidiol (THC/CBD) ratio. While THC is psychoactive, CBD is not, and a higher ratio of the latter is normally preferred for medical marijuana. One strain of cannabis, bred to have particularly low amounts of THC (less than 0.4 %) is known as Hemp, and is favored for its fibers used for clothing and other nonmedicinal purposes. Overall, it is vital for medicinal users to realize the strength of the cannabis and to appreciate the relative concentrations of cannabinoids.

Sample Preparation

Based on solid phase extraction, the QuEChERS method is practical for the analysis of mycotoxins, pesticide, cannabis actives, and terpene and is increasingly being used on more difficult plant matrices including cannabis. However, this method is a manual multi step process, and can be time consuming.

An alternative method, known as Headspace solid-phase microextraction (HS-SPME) can be used to identify and quantify terpene content in cannabis. The HS-SPME method is superior to solvent extraction as it is non-destructive to the sample, has no interference from a coextracted matrix, and provides a cleaner analysis.

Energized Dispersive Guided Extraction (EDGE)

EDGE™ is an alternative method 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. Using the EDGE™ method, a difficult sample can be extracted in one automated step, including dispersive solid phase clean up.

With EDGE™, extraction and clean-up can be carried out in one step, as both the sample and sorbents are together in one sample cell. The sample can be extracted in under 5 minutes using Q-Cup Technology, which performs both extraction and clean-up of the sample.

After collection, the extract is filtered and cooled before it is ready for analysis. EDGE™ offers the fastest possible extraction of pesticide, cannabinol, mycotoxin or terpene in one simple method. EDGE™ is inexpensive, rapid and convenient.

Q-Cup Technology

Q-Cup Technology combines the process of Dispersive Solid Phase Extraction and Pressurized Fluid Extraction in a single instrument for fast and efficient extraction, allowing different samples to be quickly extracted. Extractions in the EDGE™ are carried out at elevated temperatures and under pressure, which speeds up reaction kinetics.

In addition to faster desorption of the analytes from the matrix, sample heating and cooling is carried out in only a few seconds using a special process. Accelerated solvent extraction with EDGE is faster than QuEChERS, Soxhlet, classical ASE, ultrasound, or other conventional extraction methods, and requires less solvent and considerably less effort.

The extraction cell Q-Cup has a unique open cell concept, containing a porous Q-disk on the bottom. The sample to be examined is loaded into the Q-Cup, after which the Q-Cup is loaded into the autosampler. The Q-Cup is transported into the sample chamber using the gripper arm and is then automatically pressure-tight sealed.

After the addition of solvent, the cell is heated to a maximum temperature of 180 °C with elevated pressure. It is then kept under constant conditions for two minutes to disperse the analytes out of the sample. The solvent extract is then automatically filtered using the Q-Cup Disc, after which it is cooled down and transferred into the collection vial.

Analysis

The analysis of pesticide residue in cannabis plant material is accomplished using sensitive and selective detection techniques, such as GC and LC MS/MS. Both GC and LC are required as some pesticides can only be reproducibly detected at sufficiently low levels by one or the other, although many pesticides can be detected by both.

High selectivity is required for trace pesticide analysis and MS/MS is used to counter the complex matrix. The preparation of samples, and the clean-up of EDGE is essential to minimize ion suppression. Due to the low detection limits required, the analysis of Mycotoxins is a challenge, and affinity-based sample preparation with HPLC or LC-MS/MS is most often used. The majority of analyses are potency tests, typically conducted with UHPLC. As the cannabinoids are mainly present in their acidic form in the plant material, UHPLC is preferred over GC.

Analysis of Trace Metals

It is well known that certain heavy metals can have damaging effects on human health. If released into the environment, toxic heavy metals such as cadmium, lead, arsenic, and mercury are persistent and can accumulate in cannabis plants. As such, cannabis-based products such as foods, tinctures, oils, and salves should be tested for the presence of heavy metals to ensure the safety of patients and the quality of products.

Elemental Analysis using the MARS 6

For sample preparation of cannabis in trace metal elemental analysis, the MARS 6 microwave digestion system is the system of choice. Integrated sensor technology is used by the MARS 6 to recognize the vessel and sample number, which is then used to create a custom algorithm to ensure a custom digestion process.

The MARS 6 is a batch acid digestion microwave system with options for remote system control and contactless all vessel temperature control. Up to 40 samples can be heated during the same run. Solid sample matrices can be dissolved into an aqueous liquid using the microwave technique. Samples are placed in a concentrated acid matrix in a closed vessel, and exposed to microwave irradiation.

In these conditions, both the rate of thermal decomposition of the sample and the solubility of metals are increased. Once these metals are in solution, quantitative and qualitative analysis can be carried out using spectroscopic techniques. Using the MARS 6 acid digestion process, sample preparation time can be cut by 50 – 75 % compared to using hot plates.

Cannabis

The regulation and marketing of cannabis as a legal medical product is set to bring new challenges. New cannabis products must adhere to the highest levels of safety. It is likely that more strict regulations will be implemented in the future, resulting in a safer product. This will depend upon good analytical methodology. The use of EDGE and the MARS microwave system for the preparation of cannabis samples will provide a good basis for consistent sample 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).

This information has been sourced, reviewed and adapted from materials provided by CEM - Analytical

For more information on this source, please visit CEM - Analytical.

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