Solid-phase extraction (SPE) is a sample preparation process that separates specific chemical compounds from a solution using solid material usually in the form of a cartridge or column.
Whatever the intended compound for extraction may be, SPE uses chromatography and differential migration: fluid movement of a solute (the dissolved substance) between a solid phase and a liquid/gas phase based on affinity (how well the two stick together). The end result is the separation of the analyte from a multi-faceted chemical mixture. Thus, one can isolate a single chemical component out of an endless array of impurities or other matrix constituents.
The usage of SPE to test pesticide percentages in cannabis products is an excellent example of how effective SPE methodologies are when properly used. Due to the fact that there is no federal standard on pesticide contamination of cannabis products, it is left entirely to each state to decide what an acceptable level for pesticides and contaminants will be.
Thus, for states with varying standards of pesticide levels in cannabis products, having an effective method for identifying said contaminants is of the utmost importance. Legal authorities aren’t the only people out there who can tout the uses of this technology.
Cannabis brands can also laud the abilities of SPE to provide an undiluted and safe product for consumers. One study showed the power of combining supercritical fluid extraction with SPE.  The extraction of cannabis with CO2 produced a crude extract with nearly 38% delta-9-tetrahydrocannabinol (THC). Using just one SPE processing step augmented the potency to 90% THC.
In a presentation outlining the SPE process, Sigma Aldrich Corporation mentioned that the chief advantages of SPE are larger selectivity in sample targets, good reproducibility, and the ability to automate. The possibility of automation could be a game changer for cannabis entrepreneurs looking to maintain a steady flow of products into the marketplace without sacrificing safety and testing.
As SPE methodologies continue to be explored by the cannabis industry, we will begin to see just how effective they truly are. But current applications are quite promising.
Reference Gallo-Molina, A. et al. “Extraction, isolation and purification of tetrahydrocannabinol from the Cannabis sativa L. plant using supercritical fluid extraction and solid phase extraction”, The Journal of Supercritical Fluids, Volume 146, 2019, pp. 208-216. [journal impact factor = 3.481; cited by 3]
Photo courtesy of NPR