A Comprehensive Approach to Pesticide Residue Analysis in Cannabis

June 19, 2018
Volume: 
1
Issue: 
2
Abstract / Synopsis: 

As the number of U.S. states allowing the adult use of cannabis and cannabis products increases, so does the need for product testing before retail sale. States that have legalized recreational use have specified testing requirements for pesticide residues in cannabis flower and cannabis products. Because the specific pesticides and action levels vary from state to state, a comprehensive approach to residue analysis can meet the requirements of multiple U.S. state regulations with a single analysis. The challenge of quantifying pesticide residues in cannabis is complex because of the high concentration of cannabinoids and terpenes relative to the levels of pesticides that may be present. Here we present a straightforward acetonitrile extraction using a solid-phase extraction (SPE) cartridge and targeted dispersive solid-phase extraction (dSPE) cleanup. The final dilute extract is analyzed with both gas chromatography–tandem mass spectrometry (GC–MS/MS) and liquid chromatography–tandem mass spectrometry (LC–MS/MS) for a comprehensive target list (200+ compounds) that encompasses those identified on individual U.S. state lists. Limits of quantitation meet or exceed individual U.S. state requirements.

For U.S. states that have legalized the recreational or medicinal use of cannabis and cannabis products, there are presale testing requirements meant to address quality and consumer safety (1–3). In the absence of guidance at the federal level, states must establish the scope of the required testing in addition to any minimum or maximum values before product release into the marketplace. These compliance efforts, combined with the lack of true consensus methods, allow individual laboratories to develop analytical methodology that typically only meet the regulatory requirements of the single state where the laboratory is located.

Conventional agricultural commodities are subject to U.S. maximum residue levels (MRLs) for pesticides labeled for use on each specific commodity. These MRLs are established by the U.S. Environmental Protection Agency (EPA) as part of the pesticide registration process. Commodities destined for international export will be subject to the MRLs established by the importing country. With a wide range of commodities, pesticides, and MRLs, a comprehensive approach to residue testing is necessary to ensure the commodity complies with all applicable regulations. This comprehensive approach to pesticide residue analysis can be applied to cannabis and cannabinoid products. U.S. states with approved cannabis sales have developed target lists for pesticides with associated “action levels.” An action level is not an MRL, but rather a subjective number assigned by state regulators to establish criteria for laboratory testing. These action levels were determined by a combination of factors such as laboratory capabilities, analytical techniques, and evaluating MRLs from other commodities (4,5). Additionally, U.S. states have language in statutes or administrative rules that prohibit any pesticide from being applied off-label (that is, not following product label instructions) to any crops. Pesticide products not included on a state list could potentially be applied during cannabis cultivation. Because U.S. state regulations require a limited scope targeted testing procedure, these residues would not be discovered during presale screening and would find their way into the final consumer products on retail shelves.

QuEChERS (quick, easy, cheap, effective, rugged, and safe) is a common approach for the extraction of pesticide residues (6,7), and has been applied to both cannabis and cannabis products. Although it generates acceptable results for most pesticides in cannabis, it was developed for samples that contain greater than 70% moisture. Cannabis flower typically contains 10–15% moisture so the addition of water to each sample is necessary to generate the desired partitioning that is the principle of the QuEChERS technique. Moreover, the addition of water and salts in the QuEChERS approach generates an exothermic reaction and an increase in pH—both of which can degrade sensitive pesticides. An alternate approach is a serial extraction using acetonitrile and a solid-phase cleanup step (8). This procedure results in less coextracted material and improved recoveries for the more polar pesticides.

The general trend among testing laboratories is to develop analytical methods using a single extraction followed by analysis using tandem quadrupole mass spectrometers. With the limited scope of many U.S. state regulatory lists, liquid chromatography–tandem mass spectrometry (LC–MS/MS) is often the choice when a single instrument is used. For a true comprehensive residue analysis, a dual-platform MS/MS scheme should be developed using both gas chromatography–tandem mass spectrometry (GC–MS/MS) and LC–MS/MS. This approach allows laboratories to evaluate compounds on each platform to optimize sensitivity and chromatographic performance. Many compounds can be identified and quantified using both techniques, giving laboratories orthogonal confirmation for difficult sample matrices. 

The challenge with pesticide residue analysis in cannabis is the concentration difference between the pesticide residues and those of the coextracted cannabinoids and terpenes. These coextracted materials complicate residue testing by introducing matrix effects in the MS/MS system, and lead to increased system maintenance and instrument downtime. To address these issues, both MS/MS platforms need to have sufficient sensitivity to allow for large dilution factors that will reduce matrix effects and maintenance while meeting state-specific action levels.

References: 
  1. Oregon Administrative Rules 333-007-0400.
  2. California Code of Regulations, Title 16, Division 42. Bureau of Cannabis Control, Chapter 11, § 5719.
  3. Washington Administrative Code 246-70-050.
  4. D.G. Farrer, “Technical report: Oregon Health Authority’s Process to Decide Which Types of Contaminants to Test for in Cannabis” (Oregon Health Authority, 2015).
  5. J. Konschnik, H. Krug, and S. Kassner, Cannabis Science and Technology 1(1), 42–47 (2018).
  6. AOAC Official Method 2007.01, Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate, Gas Chromatography/Mass Spectrometry and Liquid Chromatography/Tandem Mass Spectrometry, First Action 2007.
  7. CSN EN 15662, Foods of Plant Origin - Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extraction/Partitioning and Clean-Up by Dispersive SPE - QuEChERS-Method.
  8. M.J. Hengel, J. Am. Soc. Brew. Chem. 69(3),121–126 (2011).
  9. F.J. Schenck and J.W. Wong in Analysis of Pesticides in Food and Environmental Samples, J.L. Tadeo, Ed. (CRC Press Inc., Boca Raton, Florida, 2008), Chapter 6.
  10. M. Anastassiades, D.I. Kolberg, E. Eichhorn, A. Benkenstein, S. Lukacevic, D. Mack, C. Wildgrube, I. Sigalov, D. Dörk, and A. Barth, “Quick Method for the Analysis of Numerous Highly Polar Pesticides in Foods of Plant Origin via LC-MS/MS involving Simultaneous Extraction with Methanol (QuPPe-Method),” Version 8.1, EURL-SRM, March 2015.

Rick Jordan is the Laboratory Manager at Pacific Agricultural Laboratory in Sherwood, Oregon. Daniel Miller is the Technical Director at Pacific Agricultural Laboratory. Lilly Asanuma is a chemist at Pacific Agricultural Laboratory. Anthony Macherone is a Senior Scientist with Agilent Technologies and a visiting professor at The Johns Hopkins University School of Medicine. Direct correspondence to: [email protected]

How to Cite This Article

R. Jordan, L. Asanuma, D. Miller, and A. Macherone, Cannabis Science and Technology 1(2), 26-31 (2018).