Detection of pesticides in cannabis flowers: a comparative study utilizing DART®-MS, LC-MS/MS, and QuEChERS
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Abstract
Cannabis has been used for thousands of years, though only recently has its use become more accepted and even legalized in some states. Cannabis is a schedule I substance and is considered federally illegal. Each state legislature can regulate the production, sale, and consumption of cannabis along with cultivation practices and the use of plant growth regulators or pesticides. With the lack of restrictions and required testing, there is minimal standardized testing for pesticides with limited development of novel analytical methods. The quick, easy, cheap, effective, rugged, and safe sample preparation method known as QuEChERS has shown to be a promising and effective method for the isolation of pesticides. This is a dispersive SPE method to preconcentrate the pesticides and can be modified depending on the sample matrix. In this study, two different methods for sample clean up within QuEChERS were compared along with a solvent extraction of five separate strains of cannabis flower. Instrumentation included ambient ionization using direct analysis in real time coupled to a single quadrupole mass spectrometer (DART®-MS) and liquid chromatography - tandem mass spectrometry (LC-MS/MS).
Method optimization was performed using a 16-component standard pesticide mixture on both instruments. The DART®-MS instrument required a higher concentration of the standard mixture due to a decrease in sensitivity in comparison to the LC-MS/MS approach. Sample preparation was performed with QuEChERS extractions with one clean-up method containing ChloroFiltr® and one without. Solvent extractions were also performed in both acetonitrile (ACN) and methanol (MeOH). Because the DART® instrument is coupled to a single quadrupole, the scan will detect all ions present in the sample along with any background ions from the ambient environment. In solvent extraction, the most intense peaks corresponded to THC and CBD followed by THCA and CBDA. When utilizing the QuEChERS procedure, the CBD and THC peaks were still present, but the THCA and CBDA peaks were significantly diminished. There were many peaks at a relatively small intensity that, without an analyte library, couldn’t be identified. This suggests DART-MS could potentially serve as a general screening technique for pesticide residues. LC-MS/MS was also used to analyze the effectiveness of both QuEChERS extraction techniques and the solvent extraction with both an ACN mobile phase and a MeOH mobile phase. The QuEChERS extractions did not show a significant difference between utilizing the ChloroFiltr® or not. The QuEChERS extraction detected significantly more analytes than the solvent extraction, and the MeOH mobile phase showed much higher ion counts compared to the ACN.
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