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The Use of Dispersive Solid Phase Extraction in the Detection of Pesticides in Cannabis Flower by GC-MS/MS

Adam Floyd1, Kirk R. Jensen2, Craig D. Sergeant2, A. John Dane2, Josh Cosgrove1, and Mike Tunis1
1Think20 Laboratories, Irvine, CA  2JEOL USA, Inc. Peabody, MA


INTRODUCTION

As recreational and medical cannabis use becomes legalized in more jurisdictions, more pesticides are being used in the cultivation of Cannabis. Because certain pesticide residues can pose significant health risks to consumers, pesticide analysis of Cannabis in California is highly regulated by the Bureau of Cannabis Control (BCC). All legal Cannabis products sold in California must undergo analysis for sixty-six regulated pesticides. The action limits of these pesticides vary depending on their classification and perceived danger to human health. Extracted Cannabis matrix is notoriously difficult to work with as there are significant interferences present which hinder the low-level detection of pesticides. 

This study presents a comprehensive method for the analysis of gas chromatograph (GC)-amendable pesticides in Cannabis flower. Furthermore, this method uses dispersive solid phase extraction (dSPE) to help mitigate matrix effects that are common in the flower extract. Three selected reaction monitoring (SRM) transitions were used for each target pesticide. This study was focused on developing a robust and sensitive method for GC amendable pesticides in Cannabis flower for use in the state of California. However, LC-MS/MS would also be required to analyze the complete California pesticide list.

EXPERIMENTAL

Sample Preparation:
Cannabis flower was ground and extracted using a mixture of acetonitrile and dimethylacetamide (DMA). The sample was spiked with a 20 ppb pesticide standard mixture consisting of the 12 compounds listed in Table 3. The extraction and dSPE workflow are outlined in Figure 1. The use of dSPE is critical for reducing matrix effects and allowing for low detection limits as shown in Figure 2.


Fig 1
. Sample preparation of Cannabis flower.


Fig 2
. Cannabis matrix effects before (top) and after (bottom) using dSPE.


Table 1
: Gas Chromatograph Parameters


Table 2
: Mass Spectrometer Parameters

Instrumentation:
An Agilent 7890B GC combined with a JEOL JMS-TQ4000GC triple quadrupole mass spectrometer was used in this study. All injections were done using pulsed splitless liquid injection. Analysis parameters and SRM channels are detailed in Tables 1–3.

RESULTS

The SRM chromatograms for the three transitions of every pesticide tested are shown in Figures 3 – 14.  Strong signals were observed for all pesticide transitions at 20 ppb with very little interference effects.  These results clearly show that this extraction/dSPE method combined with GC-MS/MS can readily handle the action limits for GC amenable pesticides as set forth by California regulations.

CONCLUSIONS

This study showcases a rapid, sensitive, and effective method for testing GC amenable pesticides in Cannabis matrix. The use of a dSPE sample cleanup step coupled with GC-MS/MS allows for the rapid, selective screening of Cannabis products. Furthermore, low detection limits were achieved using this scenario, which in turn allows for larger dilution factors to further mitigate matrix effects. Using dSPE also allows for greater sensitivity and better chromatographic peak shapes by removing interference compounds. These results show that each pesticide can be measured at 20 ppb in cannabis matrix and that the action limits put forth by the State of California are readily achievable using this method. Furthermore, a combination of GC-MS/MS and LC-MS/MS will provide the best all-around capabilities for analyzing the entire California pesticide list.


Table 3
: SRM Transitions


Fig 3
. SRM chromatograms for boscalid.


Fig 4
. SRM chromatograms for cis-chlordane


Fig 5
. SRM chromatograms for trans-chlordane.


Fig 6
. SRM chromatograms for chlorfenapyr.


Fig 7
. SRM chromatograms for fipronil.


Fig 8
. SRM chromatograms for kresoxim-methyl.


Fig 9
. SRM chromatograms for methiocarb.


Fig 10
. SRM chromatograms for propoxur.


Fig 11
. SRM chromatograms for chlorpyrifos.


Fig 12
. SRM chromatograms for diazinone.


Fig 13
. SRM chromatograms for dimethoate.


Fig 14
. SRM chromatograms for pentachloro-nitrobenzene (PCNB).

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