Pesticide Analysis in Cannabis using QuEChERS Extraction

QuEChERS extraction is a reputable food and agriculture testing method that is now used by analytical labs for cannabis pesticides analysis

Food safety has become a top priority as food importing and processing have grown in abundance. Due in part to this growth, increasingly efficient methods for food testing have become necessary to test for the presence of pesticides and other residual compounds in a greater number and variety of food sources. These concerns extend to the growing cannabis industry as well and the myriad of consumables that have become available in recent years — a trend that is certain to continue as more states adopt cannabis friendly regulations.

Pesticides are frequently necessary to prevent crop damage by mold and insects, however, the persistence of even trace amounts can pose a danger to consumers. Currently, states enforce individual recommendations for pesticides use and levels. These mandates do not yet extend to federal oversight by the EPA or other regulatory bodies. To ensure state specifications are met, and to prepare for future federal oversight, highly sensitive and selective methods must be specifically adapted or developed for cannabis.

Robust liquid-liquid extraction using a technique such as QuEChERS (Quick, Easy, Cheap, Effective, Robust, Safe) has shown to be an effective method for food safety analysis — modifications of which are used for cannabis product related pesticides testing as well.

The QuEChERS Extraction Method

The sample is first homogenized in a blender or (cryo)mill and placed in a vessel. Acidified acetonitrile is added to the material (1:1 with solution or with added water) and incubated with shaking and/or homogenizer balls if necessary. After incubation, QuEChERS salts are added and the mixture is shaken or vortexed, followed by centrifugation.

A key to the method is that although acetonitrile is miscible in water, it is salted out during the extraction process, thereby permitting the separation of organic compounds and water-soluble matrix materials. The resultant extract of the QuEChERS process has four layers:

1. The top extract containing organic compounds and pesticides; 
2. the insoluble matrix component layer; 
3. the water-soluble matrix components; 
4. the excess extraction salts at the bottom.

For pesticide analysis, a clean up step using a dispersive solid phase extraction (dSPE) kit provides further conditioning of the extract. This method improves performance by pulling out further interfering matrix components, while removing excess water to improve analyte partitioning. The resultant extract can be dried under nitrogen and resuspended in an appropriate solution for HPLC, GC-MS or LC-MS analysis. Quantitation, as discussed in subsequent articles, typically requires the use of analytical standards appropriate for the chosen analytical platform.

Several groups have applied extraction modifications to selectively isolate and analyze a greater number of pesticide residues from a wider variety of plants and consumables. Modifications of the salts and solution components lends to QuEChERS methods tailored toward the pesticides of interest. For instance, buffered extraction salts are amenable to more labile pesticides. Dispersive kit components are associated with removal of specific matrix components, such as organic acids, sugars, and lipids. Finally, standardized methodologies such as those approved by the Association of Official Analytical Chemists (AOAC) or the European Committee for Standardization (CEN) often dictate which kits and components are compatible with appropriate performance guidelines.

The Growing Importance of Cannabis Pesticides Analysis

The data produced by high-performance instruments are only as solid as the quality of analyte material going in. With a greater range of compounds and concentrations used as pesticides in modern food production, it is imperative that analytical labs achieve the sensitivity and reliability needed to maintain high quality food safety. Modern methods aim to achieve greater depth of sample extraction in this regard.

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Updated May 2022