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High Quality Analysis of Pesticides in Marijuana
Using QuEChERS, Cartridge SPE Cleanup, and GCxGC-TOFMS
By Jack Cochran, Julie Kowalski, Sharon Lupo, Michelle Misselwitz, and Amanda Rigdon
• Quickly and effectively extract medical marijuana samples for pesticide analysis.
• Cartridge SPE cleanups of dirty extracts improve GC inlet and column lifetimes.
• Selective GC columns increase accuracy of pesticide determinations for complex samples.
Over a dozen states in the U.S. have legalized medical marijuana
because of therapeutic benefits for ailments such as cancer, multiple
sclerosis, and ALS. Dosing methods include smoking or vaporizing
and baked goods. Unlike other prescribed medicines regulated by
U.S. FDA, marijuana is a Schedule 1 drug and is illegal on the federal
level. As a result, medical marijuana patients have no safety assur-
ances for their medication, which could contain harmful levels of
pesticide residues. Currently, medical marijuana pesticide residue
analysis methods are poorly defined and challenging to develop due
to matrix complexity and a long list of potential target analytes.
In order to address matrix complexity, we combined a simple
QuEChERS extraction approach with cartridge SPE (cSPE) cleanup,
followed by GCxGC-TOFMS. Acceptable recoveries were obtained for
most pesticides, and incurred pesticide residues were detected in
some of the illicit marijuana samples used for method development.
QuEChERS Extraction Saves Time and Reduces
Hazardous Solvent Use
Trace residue extraction procedures from dry materials like marijuana
typically involve large amounts of solvent, long extraction times, and
tedious concentration steps similar to the Soxhlet procedure or
multiresidue methods from the Pesticide Analytical Manual.
QuEChERS, with its simple 10 mL acetonitrile shake extraction and
extract partitioning with salts and centrifugation, offers time savings,
glassware use reduction, and lower solvent consumption.
Water was added to finely ground, dry marijuana samples to increase
QuEChERS extraction efficiency, especially for more polar pesticides.
A vortex mixer was used to shake the solvent and sample for at least
30 minutes prior to extract partitioning. When finished, it was easy to
transfer the supernatant from the QuEChERS extraction tube for sub-
sequent cSPE cleanup prior to analysis with GC or LC (Figure 1).
Cartridge SPE Cleanup Improves GC Inlet Uptime
Injecting chlorophyll-laden extracts into a GC gives reduced recoveries
for less volatile pesticides, and results in degradation of sensitive pesti-
cides like DDT and Dicofol (Table I). SPE cleanup with a 500 mg graphi-
tized carbon black/500 mg PSA cartridge removes chlorophyll and traps
fatty acids that interfere with qualitative pesticide identification and bias
quantification. cSPE has increased sorbent capacity over dispersive SPE
for thorough cleanup of complex extracts.
Figure 1: A quick and easy QuEChERS extraction, combined with cSPE, effectively prepared extracts for pesticide residue analysis from
highly complex marijuana samples.
A. Post-centrifugation
QuEChERS
extracts
B. QuEChERS
extracts loaded
on SPE cartridge
C. Final extract
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