High Quality Analysis of Pesticides in Marijuana using QuEChERS, Cartridge SPE Cleanup, and GCxGC-TOFMS

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.

Cartridge SPE cleanup of QuEChERS extract of marijuana. Note chlorophyll removal from cleaned extract on right.

Cartridge cleaned QuEChERS marijuana extract (top) and uncleaned extract (bottom) analyzed with GCxGC-TOFMS (Rxi-5Sil MS x Rtx-200 columns).

Cartridge SPE cleanup (top) of marijuana extract showing removal of fatty acids versus uncleaned extract (bottom) as analyzed with GC-TOFMS.

GCxGC-TOFMS of pesticide standard using an Rxi-5Sil MS x Rtx-200 column combination.

Zoom of GCxGC-TOFMS chromatogram showing select pesticides. Notice the excellent separation in both 1D and 2D spaces with the Rxi-5Sil MS x Rtx-200 column combination.

Separating Tebuthiuron from matrix interferences in a QuEChERS marijuana extract using GCxGC.

Pesticide recoveries from cartridge cleanup of QuEChERS marijuana extract (spiked immediately before cleanup; column 1), and two samples spiked before QuEChERS extraction and cartridge cleanup (columns 2 and 3). Generally, recoveries are very good. I is incurred pesticides.

Pesticides, and their concentrations, found in marijuana samples with QuEChERS, cartridge SPE cleanup, and GCxGC-TOFMS.

GCxGC-TOFMS chromatogram of cypermethrins (noted by black peak markers) as incurred pesticides in a marijuana extract. The quantification mass 163 is plotted. Note the interferences resolved by using GCxGC.

Cypermethrin mass spectrum (deconvoluted) matches well with a Reference Spectrum, confirming incurred pesticide in QuEChERS marijuana extract.

5 Responses to “High Quality Analysis of Pesticides in Marijuana using QuEChERS, Cartridge SPE Cleanup, and GCxGC-TOFMS”

  1. […] possibly fingerprinting marijuana types, (2) characterize marijuana potency, and (3) analyze for pesticides in marijuana with GCxGC-TOFMS and […]

  2. […] impact on LC-MS/MS analysis by dirtying the source prematurely, so recently when analyzing some QuEChERS marijuana extracts for pesticides, we employed GCB dSPE.  We used 3 dSPE formulations that contained 2.5, 7.5, and 50 mg GCB, along […]

  3. […] post I told you about our experimentation with marijuana (that didn’t sound right…) and pesticide extraction via QuEChERS.  An important part of that work was cartridge solid phase extraction (cSPE) cleanup with 500mg […]

  4. Ahmad says:

    What does PSA stand for

  5. Jack Cochran says:

    Primary Secondary Amine (PSA) is a type of sorbent material used to remove fatty acids and sugars, mainly, from QuEChERS extracts via dispersive solid phase extraction (dSPE). The PSA is bonded on silica particles. Simple shaking of a QuEChERS extract with PSA followed by centrifugation produces a “just clean enough” extract to analyze via GC or LC.


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