In the cannabis industry, there is always more need of validated methods for terpene analysis. While many extraction and detection techniques have been investigated, there is a lack of systematic research on modern cannabis extraction methodologies like accelerated solvent extraction (ASE) and introduction techniques such as direct immersion solid-phase microextraction Arrow (DI-SPME Arrow).
ASE allows the recovery of analytes from the sample matrix using high temperature and pressure to improve extraction efficiency, saving time and solvent in comparison with other extraction techniques. [1] Solid-phase microextraction (SPME) permits quick sample preparation and offers an efficient method to sense chemicals in detection and separation systems. [2] DI-SPME is, in general, less sensitive than headspace (HS) SPME for more volatile compounds; in the former introduction technique, the polymeric fiber (coated with silica) is immersed in a small volume of the liquid-extracted sample instead of being in contact with the gas phase of the sample. [2] Arrows are upgraded options compared to fibers in that they have greater surface area and more phase volume. Injection syringes are considered traditional, less modern options, and injection may be conducted via headspace or liquid.
In a recent study by Myers et al [3], researchers focused on the implementation of terpene extraction using the Dionex™ Accelerated Extractor (ASE™ 350) on cannabis flowers and hop pellets. The method was run at 75°C and 1500 psi (103 bar) using isopropanol as the solvent. When hand shakeout extraction (“manually intensive” using vortexing, sonication, and centrifugation) was compared to ASE, the second was preferred due to reduced disposable waste and more analytical consistency via the absence of user variability. Terpenes were removed from hop pellets using a proprietary cleaning solvent such that the terpene-free hops could be used as a surrogate matrix match to cannabis inflorescences: in organic analysis, the use of surrogates is important to check whether analyte recovery is influenced by the physical/chemical characteristics of the sample to assure a precise and reliable quantification of target compounds. This was the first study to use hops in this way, providing a “viable technique.”
The analyses were performed using gas chromatography coupled with mass spectrometry (GC-MS). The evaluation of sample introduction techniques was done based on relative compound response using reference terpene standards.
Contrary to expectations, on cannabis sample preparation for terpene analysis, DI-SPME Arrow appeared to be preferable to HS-SPME Arrow because of better responses and precision/reproducibility, in particular for high molecular weight terpenes. DI-SPME and liquid injection-syringe (LI-Syringe) were proven to be valuable methods for terpene extraction from cannabis flower, both providing better results than HS-SPME and HS-Syringe. Overall, “The LI-Syringe approach was deemed the most straightforward and robust method…” and provided the “more complete chemovar profile of cannabis flower and at higher concentrations.” The HS-Syringe only picked up 13 of 23 quantified terpenes, failing when it came to sesquiterpenes. In fact, the researchers recommended reconsidering its widespread use by laboratories. They also noted that arrows must be routinely replaced, a key disadvantage.
Further research on the systematic comparison between extraction and injection techniques should be done to fully exploit the potential of traditional and modern methodologies.
References:
[1] Giergielewicz-Możajska H, et al. Accelerated solvent extraction (ASE) in the analysis of environmental solid samples — Some aspects of theory and practice. Critical Reviews in Analytical Chemistry. 2001;31(3):149-165. DOI: 10.1080/20014091076712 [Times cited=165 (Semantic Scholar); Journal impact factor = 4.568][2] Al-Khshemawee H, et al. Application of direct immersion solid-phase microextraction (DI-SPME) for understanding biological changes of Mediterranean fruit fly (Ceratitis capitata) during mating procedures. Molecules. 2018;23(11):2951. doi: 10.3390/molecules23112951 [Times cited = 9; Journal impact factor = 3.267]
[3] Myers C, et al. Accelerated solvent extraction of terpenes in cannabis coupled with various injection techniques for GCMS analysis. Front Chem. 2021;9:619770.
doi: 10.3389/fchem.2021.619770 [Journal impact factor = 3.693]
Image: ThermoFisher Scientific
