Of the hundreds of unique phytochemicals in cannabis, terpenes form the largest group with over 100 currently identified. Like cannabinoids, many terpenes are of medicinal interest having properties ranging from anti-inflammatory to antimicrobial effects. In addition, terpenes can enhance (or antagonize) the effects of certain cannabinoids through a synergistic effect, by modulation of cannabinoid receptor interactions, increased blood brain barrier permeation, and other modes of action.
Terpenes are responsible for the odor and flavor of cannabis and the presence of varying concentrations of individual terpenes are strain specific. The compounds are classified in diverse families according to the number and arrangement of 5-carbon units (isoprene units) -- monoterpenes have 10 carbons, sesquiterpenes have 15, and triterpenes derive from a 30-carbon structure.
Monoterpenes including D-limonene, β-myrcene, and β-pinene dominate the volatile terpene fraction. Along with the sesquiterpenes, β-caryophyllene, α-humulene, and others, these occur in large proportions in cannabis extracts. Terpenes in general are secondary metabolites and are present in largely the same location as most cannabinoids, the glandular trichomes of the cannabis flower. Thus, they are present in varying levels during the harvest and processing of cannabis and cannabinoid compounds.
It is clear that accurate identification and quantification of terpenes is both relevant and important. As evolving state regulations have led to an increase in cannabinoid testing and profiling methodologies, terpenes have been the subject of this as well, with several states now including terpene profiling in their guidelines for cannabis testing.
The preferred method for analyzing these aromatic compounds is by GC or GC-MS. In profiling a panel of compounds from a cohort of samples, a front-end device such as a head space autosampler is advantageous to support a steady workflow. Advanced methods such as the full evaporation headspace technique (FET) are designed to permit analysis of material that does not dissolve in solvent.
A capillary GC with a split flow inlet permits analysis of high concentration compounds and standards without sacrificing performance and sensitivity. Finally, the small molecule secondary metabolite chemistry of terpenes is consistent with the use of a single quadrupole mass spectrometer for downstream analysis.
Analytical standards relative the terpene panel are used to construct a calibration curve, which is checked for linearity and reproducibility. From this the terpene concentrations can be measured. These methods permit not only quantitation but the identity and relative concentrations of terpene analogs and coeluting species. This may be important as it has been shown that terpenes can breakdown and change over time, activities that are exacerbated by heat and light and other possible confounding factors.
Terpenes are an interesting and important constituent of cannabis as they have dominant roles in the flavor and aroma as well as the medicinal qualities of the plant. As the significance of terpenes becomes further evident, and as states continue to add terpene profiling to testing guidelines, accurate and precise methods for terpene analysis will become more and more important.