Sample Preparation Methods for Cannabis Analysis

Today’s era is changing, and the decriminalization and legalization of marijuana in many countries have ushered in new markets for cannabis, and cannabis-infused products. These range from personal care, to foods, to other medicinal formulations.

Cannabis

Cannabis. Image Credit: Dmytro Tyshchenko/Shutterstock.com

To ensure the legitimacy of these products, and to control against illicit variants of cannabis, the sample preparation methods of high Ion mobility spectrometry (IMS) Ion mobility spectrometry- Mass Spectrometry (IMS-MS), and Stir Bar Sorptive Extraction (SBSE) will be explored.

Ion mobility spectrometry (IMS)

Primary research performed by Marianne Had̈ener et. al, highlight the boons of high ion mobility spectrometry (IMS). Working with cannabis extracts while implementing electrospray ionization has allowed researchers to distinguish medicinal marijuana from illicit variants of the drug.

The contrast between legal and illegal forms of marijuana is defined by Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) threshold, as demarcated under Swiss legislation. According to this bylaw, strains that hold a Δ9-THC content of 1% or greater are considered illegal by narcotics control within Switzerland, while varying amounts of high-CBD/low-THC marijuana products can be sold legally.

In addition, this apparatus can also distinguish between the controlled substrate, Δ9- THC, and its noncontrolled cannabinoid isomer (CBD), a hallmark challenge in the field of cannabis testing. The isomers THC and tetrahydrocannabinolic acid (THCA) have an ether-bridged closed ring structure, as opposed to the isomers CBD and Cannabidiolic acid (CBDA), where a cleaved ring is found, resulting in an alkene and hydroxyl group.

Even in this IMS-only mode (excluding the coupling to a mass spectrometer), the signal-to-noise ratio (S/N) may deteriorate (due in part to the longer integration time), though the cannabinoid isomers are distinguishable. A small deviation of <5% is found when compared to IMS-MS. The potency and portability incorporated in IMS require further investigation, however, this method does bring new strides in the field of cannabinoid testing.

Sample preparations within ion mobility spectrometry (IMS)

Researchers have been placing a good amount of stock into mobility spectrometry, as well as its coupling to mass spectrometry (IMS-MS). Through the drift tube of this apparatus, two different mobile phases are incorporated while testing. One was an aqueous solution of triethylammonium phosphate, while the other was acetonitrile- the buffer gas that was used was high-purity nitrogen.

All measurements were implemented using high-resolution, while the IMS cell was set to a pressure of 1000 mbar (986.9 atm) and 60 oC. Key analytes such as cannabinoids, terpenes, solvents, etc. all fall under predetermined ranges, which led to an acquisition of the mass spectra from 100 to 500 mass: charge (m/z).

The similarities in functional groups between all isomeric cannabinoids embody a hurdle for GC and LC-based techniques, leading to long run times of 15 minutes or more. This baseline separation is superlative when compared to common HPLC methods of analysis.

According to Marianne Had̈ener et. al, IMS-MS holds a negative bias for CBD, Δ9-THC, CBDA, and Δ9-THCA, maintaining a confidence interval of ∼20% for every analyte listed. It is speculated that this negative bias is directly caused by the improved selectivity of mass spectrometry when compared to the diode-array detector in archetypical HPLC systems.

Stir bar sorptive extraction (SBSE)

Both cannabis inflorescences and cannabis resins are dually extracted via supercritical fluid and are used in SBSE. Derived from sorptive extraction, this process incorporates the extraction of solutes into a polymer coating atop a magnetic stirring rod, perfect for the retrieval and enrichment of organic matter from aqueous matrices.

These Polydimethylsiloxane (PDMS) covered bars are immersed in an aqueous solution of cannabis flowers, using a thermal desorption unit (TDU) to heat the sample, followed by a cooled injection system (CIS) to allow for MS analysis.

By extracting the biological analyte in question, followed by assay via GC x GC-MS means, researchers can undergo a high-class quantitative analysis of arguably the three most important cannabinoids: Δ9- tetrahydrocannabinol, cannabidiol, and cannabinol.

Flavio A. Franchina et. al have accomplished just that, yielding correlation factors over 0.98, and a <20% reproducibility rate. This post-targeting analysis allowed for the confirmation of two different pesticides, plasticizers, and one cannabidiol degradation product throughout several different strains. This technique SBSE/ flow-modulated GC x GC-MS method, herein used in combination, is an effective approach in targeting analysis of complex samples.

Interpretable results of sample preparation

Once these three processes are accomplished, schematics such as chromatographs and heat maps are often employed, measuring the response of selected ions from varying chemical classes, such as monoterpenes, sesquiterpenes, hydrocarbons, cannabinoids, other terpenoids, and fatty acids. This will accrue a good amount of data that will help determine extraction variables (e.g., temperature, salt addition, solvent).

The following two-dimensional gas chromatography and time-of-flight mass spectrometry (GCXGC-TOFMS) graphs that result from these sample preparations are a commonly used method of determining these compounds and salts with a suitable amount of reproducibility. This creates a contour plot to display the nature of the marijuana extract. This is accomplished by elucidating which compound classes elute by displaying certain regions in 2D space where the first-dimension retention time in minutes (1tR) and second retention time in seconds (2tR), are plotted. This measuring shows the time elapsed between sample injection, and the maximum signal displayed by a compound migrating to the detector.

Sources:

  • Marianne Hädener, Michael Z. Kamrath, Wolfgang Weinmann, and Michael Groessl. High-Resolution Ion Mobility Spectrometry for Rapid Cannabis Potency Testing. Analytical Chemistry 2018 90 (15), 8764-8768
  • Flavio A. Franchina, Lena M. Dubois, and Jean-François Focant. In-Depth Cannabis Multiclass Metabolite Profiling Using Sorptive Extraction and Multidimensional Gas Chromatography with Low- and High-Resolution Mass Spectrometry. Analytical Chemistry 2020 92 (15), 10512-10520
  • Carlo Bicchi, Cristina Iori, Patrizia Rubiolo, and Pat Sandra. Headspace Sorptive Extraction (HSSE), Stir Bar Sorptive Extraction (SBSE), and Solid Phase Microextraction (SPME) Applied to the Analysis of Roasted Arabica Coffee and Coffee Brew. Journal of Agricultural and Food Chemistry 2002 50 (3), 449-459
  • Weimin Wang, Shuang Wang, Chuting Xu, Hong Li, Yuming Xing, Keyong Hou, and Haiyang Li. Rapid Screening of Trace Volatile and Nonvolatile Illegal Drugs by Miniature Ion Trap Mass Spectrometry: Synchronized Flash-Thermal-Desorption Purging and Ion Injection Analytical Chemistry 2019 91 (15), 10212-10220
  • Megan Grabenauer, Wojciech L. Krol, Jenny L. Wiley, and Brian F. Thomas. Analysis of Synthetic Cannabinoids Using High-Resolution Mass Spectrometry and Mass Defect Filtering: Implications for Nontargeted Screening of Designer Drugs. Analytical Chemistry 2012 84 (13), 5574-5581

Further Reading

Last Updated: Sep 27, 2021

Vasco Medeiros

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Vasco Medeiros

Obtaining an International Baccalaureate Degree at Oeiras International School, with higher levels in Chemistry, Biology, and Portuguese, Vasco Medeiros has just graduated from the University of Providence College with a Bachelor of Science. Before his work as an undergraduate, he first began his vocational training at the HIKMA Pharmaceuticals PLC plant in Ribeiro Novo. Here he worked as a validation specialist, tasked with monitoring the gauging and pressure equipment of the plant, as well as the inspection of weights and products.

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