Rapid Screening of Cannabinoids in Edibles Using Thermal Desorption-GC–MS

November 12, 2018
Volume: 
1
Issue: 
4
Abstract / Synopsis: 

Most of the traditional methodologies for the determination of cannabinoids are based on solvent extraction, filtration, and concentration. These techniques are cumbersome, time-consuming, and suffer from analyst-to-analyst variability while producing data of limited value. Many laboratories routinely “screen” each sample to quickly determine the potential for matrix interference and instrument contamination while providing an estimate of the target compound’s concentration. A good “screening” method is simple (that is, minimal or no sample preparation), fast (analysis in less than 5 min), and semiquantitative. This article describes how thermal desorption (TD)-gas chromatography–mass spectrometry (GC–MS) analysis eliminates conventional sample preparation regimes and can be used as a good rapid screening technique.

Most of the traditional methodologies for the determination of cannabinoids are based on solvent extraction, filtration, and concentration. These techniques are cumbersome, time-consuming, and suffer from analyst-to-analyst variability while producing data of limited value.

As the demand for the analysis of cannabinoids increases, it is imperative that the day-to-day analytical protocols be reproducible, accurate, and efficient. Many laboratories routinely “screen” each sample to quickly determine the potential for matrix interference and instrument contamination while providing an estimate of the target compound’s concentration. A good “screening” method is simple (that is, minimal or no sample preparation), fast (analysis in less than 5 min), and semiquantitative.

One of the most widely used analytical techniques for “screening” is thermal desorption-gas chromatography–mass spectrometry (TD-GC–MS) (1,2). This technique does not require any solvent extraction or sample pretreatment. Milligram quantities are put in an inert sample cup which is then “ready to analyze.” The multimode pyrolyzer with a vertical micro-furnace design allows programmable and multiple thermal desorption analysis on a single sample. This process, which refers to evolved gas analysis (EGA), starts with the acquisition of a thermal profile (that is, detector response as a function of sample temperature) of each sample type. To perform EGA, a short, deactivated tube (2.5 m, 0.15 mm i.d.) is used to connect the injection port to the MS detector. The sample is dropped into the furnace at a relatively low temperature (40–100 °C). The furnace is then programmed to a much higher temperature (600–800 °C). Compounds “evolve” from the sample as the temperature increases. A plot of detector response versus furnace temperature is obtained. Extracted ion chromatograms (EIC) are used to identify the thermal zone over which specific compounds of interest evolve from the sample. Now, these optimum TD temperatures can be used in subsequent TD-GC–MS experiments to introduce the key components of interest while minimizing introduction of the matrix. Only this portion of the sample is actually transferred (that is, injected on) to the analytical column. Injecting only a small portion of the sample provides immediate benefits to the laboratory, such as:

  • The high boiling fraction of the sample remains in the sample cup. This eliminates the need for a high-temperature bake out. Thus, column lifetime increases, there is little to no system contamination, and run-to-run cycle time decreases.
  • More sample can be put in the sample cup, which has the effect of lowering detection limits—without affecting instrument performance or cycle time.

With respect to the analysis of cannabinoids, it is important to keep in mind that TD-GC–MS is based on the volatilization of target compounds from the matrix. Those compounds that are thermally labile or easily converted to an alternative compound need to be identified. In these instances, it is the reformed compounds that are identified and monitored. Decarboxylation is forced to completion which could give the “screening determinations” higher values: the concentration range increases and dilution factors are more accurately determined.

References: 
  1. ASTM International, ASTM D7823-16: Determination of Low Level, Regulated Phthalates in Poly (Vinyl Chloride) Plastics by Thermal Desorption—Gas Chromatography/Mass Spectrometry, https://www.astm.org/Standards/D7823.htm.
  2. International Electrotechnical Commission, IEC 62321-8: Determination of certain substances in electrotechnical products – Part 8: Phthalates in polymers by gas chromatography-mass spectrometry (GC-MS), gas chromatography-mass spectrometry using a pyrolyzer/thermal desorption accessory (PY/TD-GC-MS), https://webstore.iec.ch/publication/32719.

Rojin Belganeh is the technical and marketing director for Frontier Laboratories Ltd. North America in Antioch, California. William Pipkin is the president of ATRq in Orem, Utah. Direct correspondence to: [email protected] and [email protected]

How to Cite This Article

R. Belganeh and W. Pipkin, Cannabis Science and Technology 1(4), 50-55 (2018).