Validation of a high-throughput method for analysis of pesticide residues in hemp and hemp products

Authors: MICHLIG, NICOLAS - Universidad Nacional Del Litoral; Lehotay, Steven; Lightfield, Alan; BELDOMENICO, HORACIO - Universidad Nacional Del Litoral; REPETTI, MARIA - Universidad Nacional Del Litoral

Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2021
Publication Date: 3/27/2021
Citation: Michlig, N., Lehotay, S.J., Lightfield, A.R., Beldomenico, H., Repetti, M.R. 2021. Validation of a high-throughput method for analysis of pesticide residues in hemp and hemp products. Journal of Chromatography A. 1645:462097. https://doi.org/10.1016/j.chroma.2021.462097.
DOI: https://doi.org/10.1016/j.chroma.2021.462097

Interpretive Summary: Hemp production and usage is increasing throughout North America, and pesticide residues need to be monitored in food, feed, and medicinal products generated from hemp. The aim of this work was to evaluate and validate the recently developed “quick, easy, cheap, effective, rugged, safe, efficient, and robust” (QuEChERSER) sample preparation method to determine pesticide residues in hemp plants, powders, oils, and pellets. Multi-level, multi-day validation results show that acceptable results were typically achieved for more than 90 of the 106 targeted pesticides in all but the most complex dried samples. Based on these and other findings, the QuEChERSER method is anticipated to become the most widely applied analytical method in the world for chemical residues in foods and feed, including many hemp products.

Technical Abstract: Hemp has been an agricultural commodity for millennia, and it has been undergoing a resurgence in interest and production due to its high content of cannabinoids, protein, fiber and other ingredients. For legal possession and use throughout the USA, hemp and hemp products must have delta-9-tetrahydrocannabinol (THC) concentration < 0.3%. As with most crops, pesticides may be applied when farming hemp, which need to be monitored in food, feed, and medicinal products. The aim of this work was to evaluate and validate the recently developed “quick, easy, cheap, effective, rugged, safe, efficient, and robust” (QuEChERSER) sample preparation mega-method to determine pesticide residues in hemp plants, flowers, powders, oils, and pellets. High-throughput analysis of final extracts for 106 targeted pesticides and metabolites from North American monitoring lists entailed: 1) ultrahigh-performance liquid chromatography - tandem mass spectrometry (UHPLC-MS/MS) with column back-flushing, and 2) instrument-top sample preparation + low-pressure gas chromatography (ITSP+LPGC-MS/MS). In QuEChERSER, 2 g sample is extracted with 10 mL 4/1 (v/v) acetonitrile/water by mechanical shaking for 10 min, followed by 3 min centrifugation. For LC, 200 µL of extract is taken and solvent exchanged into initial mobile phase followed by 5 min ultra-centrifugation prior to the 10 min analysis. For GC-amenable pesticides, the remaining initial extract is partitioned with 4/1 (w/w) anh. MgSO4/NaCl, and 1 mL is taken for automated ITSP cleanup in parallel with 10 min LPGC analysis. In the former case, the UHPLC column is back-flushed with 1/1 (v/v) methanol/acetonitrile for 3 min between each injection to keep the system clean and avoid ghost peaks. Multi-level, multi-day validation results show that 70-120% recoveries with RSDs < 20% were achieved for more than 80% of the analytes in hemp protein powder, oil, pellets, and fresh plant (dried hemp plant and flower were too complex). Limits of quantification (LOQs) < 10 ng/g were achieved for nearly all pesticides, yielding 2.8% false negatives among >13,000 analyte results in the spiked samples. The QuEChERSER method was demonstrated to meet the challenge for several complex hemp matrices.