Terpenes play a role in the overall smell and taste of cannabis derived products. Some people tend to only focus on THC concentration, whereas the terpenes contribute to the overall complexity and nuances with the cannabis strain. Similarly to how a beer or a wine is more than just its alcohol concentration, marijuana is much more than its THC concentration. The terpenes are believed to have potential medicinal properties and that exhibit an entourage effect with cannabinoids. There have been purported to be around 200 different terpenes (and terpenoids) in various strains of cannabis. Although, this number of 200 frequently given out seems to be inflated and lacks evidence of names and chemical structures of all 200. Monoterpenes tend to dominate the over terpene profile of natural cannabis flower. The most common terpenes found in cannabis are beta-myrcene, limonene, D-linalool, alpha-pinene, beta-caryophyllene, Nerolidol, caryophyllene oxide, phytol, humulene, terineol, and eucalyptol. However, diversity is abundant with cannabis strains and you might see less typical terpenes surpass the concentrations of these most common terpenes.
Terpene analysis and profiling can be performed through a variety of analytical methods. Terpenes are volatile, low boiling point compounds which make them a perfect candidate for gas chromatography (GC). GC is typically employed as the separation method while the sample introduction method and detector can vary. Headspace sampling or direct liquid injection can be used as the sample introduction technique. Headspace involves heading a known quantity of sample in a vial and injecting a portion of the gaseous phase in the vial. Due to the high volatility of terpenes, they are easily boiled off into gas phase, thus allowing for a clean sample introduction with minimal matrix effects. Cannabis is an incredibly dirty matrix (by GC standards) with various waxes, lipids, large concentrations of cannabinoids and other compounds. Automated headspace sampling is a great way to overcome problems associated with a dirty matrix. Direct liquid injection is the alternative method. I must preface this with saying that I do not have direct experience comparing and contrasting if one method is analytically superior to the other. Although one aspect for certain is that a lab using direct liquid injection would require more GC maintenance changing the liner of the sample introduction port. Potential false positive or inaccurate elevated values might be obtained if FID is used as the detector. Flame Ionization Detection (FID) is a non-specific method that only detects molecules based on retention time as they come off the GC column. A mass spectrometry (MS) detector can be used to add extra specificity and increased sensitivity. However, proponents of the cost effective FID technique could say MS isn’t that useful because a lot of terpenes are isomers of one another and classified as monoterpenes, diterpenes, sesquiterpenes, etc with identical mass to charge ratios. At least with the MS chromatogram, you have the mass to charge ratio and RT for unambiguous identification and quantification.