Recently we reported on what we believe is the first application of QuEChERS for marijuana, using it for potency analysis with GCxGC-TOFMS. Ultimately, the plan was to determine pesticides via the QuEChERS approach, combining it with cartridge SPE cleanup as we did for dietary supplements, since sample complexity would defeat the typical dispersive SPE cleanup used with QuEChERS.
Since 17 States and the District of Columbia now have active medical marijuana programs, which includes allowing dispensaries to sell cannabis products for smoking/vaporizing, and in the form of edibles, it won’t be long before the FDA has to get involved to evaluate the pesticide content of the medicine. And while many of the cannabis labs currently in existence purport to determine weed killers in weed, it’s unlikely they have sophisticated methods in place to look for anything but the highest levels.
We did our method development on illicit marijuana that was scheduled for destruction by the Penn State University police department, with the kind help of Randy Hoffman, a police officer there. Samples were finely ground, weighed from about 0.2 to 2 g into centrifuge tubes, wetted with solvent and water, spiked with internal standards and pesticides (if needed for recovery determinations), and extracted with a modified EN QuEChERS method. The extract was then cleaned using cartridge SPE (500 mg GCB and 500 mg PSA), mainly to remove high levels of chlorophyll that degrade GC inlet and column performance, and fatty acids that interfere with pesticides where they elute. We looked at over 80 pesticides, including those reported to be found on marijuana or used in marijuana grow operations. Recoveries overall were very good as determined using GCxGC-TOFMS, with a few exceptions.
Interestingly, but perhaps not surprisingly, we also found incurred pesticides in the marijuana samples, sometimes at ppm levels (see tables below), highlighting the need for monitoring of medical marijuana. Watch for another blog coming soon on the LC-MS/MS quantification of Bifenazate (Floramite) and Abamectin (Avid), two pesticides commonly used in indoor grow operations.