A MULTIRESIDUE APPROACH TO PESTICIDE SCREENING IN CANNABIS USING GC-MS/MS

Multiresidue Pesticide Screening in Cannabis Using GC-MS/MS

Significance of the Topic

The recent legalization of cannabis for medical and recreational use has created a critical need for reliable methods to detect trace pesticide residues in a highly complex plant matrix. Cannabis contains high levels of cannabinoids, resins and other constituents that interfere with analyte detection at ppb to ppm levels, while regulatory requirements vary widely across jurisdictions.

Objectives and Study Overview

This work presents a comprehensive, multiresidue GC-MS/MS approach designed to screen hundreds of GC-amenable pesticides in cannabis and cannabis products. The method development focused on optimizing sample extraction, cleanup procedures, chromatographic separation and ionization strategies to achieve robust selectivity and sensitivity.

Methodology

• Sample Preparation: 0.5 g homogenized cannabis flower spiked with pesticide standards and extracted with 5 mL acetonitrile using a Geno Grinder. Following centrifugation, extracts were cleaned by dispersive SPE containing MgSO₄, PSA, C18 and graphitized carbon black.
• Column Screening: Five GC columns (Rxi-5MS, Rtx-200, Rtx-440, Rxi-17SilMS and Rtx-1301) were evaluated for resolution of target pesticides from interfering cannabinoids. The 30 m Rtx-440 phase provided the best balance of resolution and thermal robustness.
• Chromatographic Conditions: Pulsed splitless injection at 250 °C, helium carrier at 2.0 mL/min, a multi-segment oven program to 330 °C over 21.1 min.
• Ionization Modes: Both electron ionization (EI) at 70 eV and atmospheric pressure GC (APGC) were compared for selectivity and sensitivity.

Used Instrumentation

• Xevo TQ-GC triple quadrupole mass spectrometer with EI source
• Xevo TQ-S micro instrument equipped with APGC source

Main Results and Discussion

Optimization of column selectivity with Rtx-440 improved peak shape and provided baseline or near‐baseline resolution of key pesticides (e.g., bifenthrin) from abundant cannabinoids such as THC. Comparison of ionization techniques showed that APGC’s softer ionization yielded higher molecular ion abundances, enabling more specific MRM transitions and substantially lower limits of detection. For example, chlorfenapyr detection in cannabis improved from 50 ng/mL with EI to well below 5 ng/mL with APGC. Quantitative recoveries for a representative panel of GC-amenable pesticides spiked into matrix ranged from 80 % to 120 %, demonstrating method accuracy and precision.

Benefits and Practical Applications of the Method

• Wide pesticide scope covering hundreds of analytes to meet diverse regulatory thresholds across states and countries.
• Enhanced chromatographic separation to mitigate extreme matrix interferences from cannabinoids.
• Dual ionization capability (EI and APGC) for flexible trade-offs between fragmentation rich spectra for library searching and high-specificity molecular ion detection.
• Robust sample cleanup protocol yielding consistent recoveries and minimal matrix effects.

Future Trends and Potential Applications

Advances in ionization technology and high-resolution mass spectrometry will further lower detection limits and simplify pesticide identification in complex matrices. Harmonization of regulatory standards may drive demand for standardized multiresidue methods. Automation and miniaturization of sample preparation workflows will increase throughput in high-volume testing laboratories.

Conclusion

The described multiresidue GC-MS/MS method combining optimized column chemistry, effective dispersive SPE cleanup and both EI and APGC ionization provides a powerful platform for sensitive, selective and comprehensive pesticide screening in cannabis. This approach addresses the unique analytical challenges posed by the cannabis matrix and supports compliance with evolving safety regulations.