During chromatographic analysis of cannabis, cannabinoids present within samples may co-elute with low-polarity pesticides often present in lower concentrations on cannabis plant materials. Current methods emphasize recovery of target analytes but report losses for some analytes during the sample clean-up process. Additionally, these methods are unable to isolate pesticides from cannabinoids and rely heavily on the sensitivity and selectivity of mass spectrometry to differentiate co-eluting analytes. Methods circumventing these issues are needed for accurate quality control. In this work, we present a new approach to extract and analyze pesticides and cannabinoids using solid-phase microextraction (SPME). SPME is capable of high enrichment factors allowing for quantification of analytes in low concentrations or with low response factors. Over the last several years, SPME sorbent coatings comprised of polymeric ionic liquids (PILs) have been developed to be compatible with gas chromatography and liquid chromatography due to their high thermal and chemical stability, low vapor pressure, and tunable hydrophobicity. As functional monomers within PILs, ionic liquids (ILs) can undergo many different and simultaneous interactions including dispersive, π-π stacking, and hydrogen bonding interactions. PIL sorbent coatings display low solubility in organic solvents and have lifetimes comparable to commercial fibers when a dicationic IL crosslinker is incorporated into the polymer network. By introducing different functional groups into the chemical structure of the ILs/PILs, sorbent coatings can exhibit selectivity towards desired analytes. In this work, we have designed imidazolium PIL-based sorbent coatings for direct immersion-SPME to isolate commonly regulated pesticides and cannabinoids from aqueous samples. PIL fibers containing 100%, 50%, and 0% benzyl moieties and a commercial PDMS/DVB fiber were investigated for their increased selectivity towards 59 pesticides compared to six cannabinoids abundantly found in cannabis, including Δ9-THC. Extraction and desorption conditions, including pH, extraction temperature, extraction time, desorption time, and desorption solvent, were optimized for both pesticides and cannabinoids using high-performance liquid chromatography. Under optimized conditions, structurally-tailored PIL sorbent coatings permitted selective extraction of detectable pesticides while minimizing the amount of cannabinoids extracted from the sample.

Analyzing pesticides and cannabinoids using polymeric ionic liquid-based sorbent coatings in solid phase microextraction coupled to high-performance liquid chromatography

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ACS Fall 2022

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