by Paul C. Winkler, David Egerton, Craig Butt, April Quinn-Paquet, K.C. Hyland, Phil Taylor, and David Monk
AL
Pesticide Testing for the Cannabis Industry: The Importance of LC-MS/MS for Obtaining Accurate Results in a Complex Matrix
In the early years, regulations for medical marijuana focused on the aspects of production, possession, and prescription.1
There was little if
any regulatory incentive to analyze cannabis samples for anything other than the major cannabinoids. When Colorado and Washington legalized adult-use marijuana in 2012,2,3
interest in testing cannabis and related
products such as concentrates and edibles grew dramatically. While cannabis samples are analyzed for a variety of items such as potency, ter- penes, microbial contamination, metals, and residual solvents, the most controversy has been related to the amount of pesticides (a term used to describe pesticides, miticides, plant growth regulators, and fungicides) present in cannabis samples.4
Pesticides are a major concern to consum-
ers and regulators due to the unknown health effects of many of these compounds, especially when inhaled.5
High-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) has emerged as the method of choice for pesticide analysis because it offers superior selectivity, sensitivity, and ruggedness and does not require extensive sample preparation before analysis. Methods have been described for the analysis of pesticides in cannabis samples using gas chromatography-tandem mass spectrometry (GC-MS/MS) that perform well but in general are applied to a smaller number of analytes than LC-MS/MS. Moreover, GC-MS/MS methods are not as robust as LC-MS/MS methods, especially in complex matrices,6,7
and some com-
pounds, such as abamectin, are not amenable to analysis by GC-MS/MS because they are heat labile and degrade in the injection source.
Analysis of pesticides in cannabis has been complicated by the lack of federal guidance. States have struggled to develop clear testing guide- lines, and the testing requirements change as the industry evolves.8,9
The
industry has responded to customer requirements for pesticide analysis, and several laboratories offer these services using LC-MS/MS analyses.
Experimental
Samples were extracted via either QuEChERS or solvent extraction using 1 g of sample extracted into 5 mL of methanol. An Exion LC AD system attached to a QTRAP 6500+ system or Triple Quad 3500 system (all from SCIEX, Framingham, MA) were used to analyze the samples. The LOQ
AMERICAN LABORATORY 10
(limit of quantitation) data were obtained using a QTRAP 6500+, and sample analyses were performed on a Triple Quad 3500. Separations were performed on a Raptor ARC-18 column (Restek, Bellefonte, PA) or Kinetex C18 column (Phenomenex, Torrance, CA) using 0.1% formic acid + 5 mM ammonium formate in water: 0.1% formic acid + 5 mM ammo- nium formate in methanol gradient.
Discussion
The first question for any method development project is: What are the target analytes and what is the maximum residual limit (MRL)? As regards pesticide analysis for cannabis, this is a more complex issue than may be expected, mainly due to the lack of federal guidelines from agencies such as the USDA that issue pesticide residue levels for crops. These agencies cannot issue guidelines for cannabis because it is an illegal substance, which leaves each state to develop its own regula- tions, and results in different guidelines and compound lists. The State of Oregon, however, has developed a list of 59 compounds with MRLs and is, to date, the only state to provide such a list.10
Others are working
to develop lists as well and, fortunately, these lists have been subsets of the Oregon list. Therefore, laboratories interested in providing pesticide analyses will ultimately need to have the capability to analyze these compounds.
All of the compounds on the list can be detected using LC-MS/MS, in contrast to GC-MS/MS, where some of the compounds require de- rivatization to survive the injection port. Typical LC-MS/MS instrumental LOQs are shown in Table 1. This table shows LOQs when the compounds are analyzed in a solvent. An LOQ of 4.5 ppb corresponds to a plant concentration of 0.1 ppm using a 0.25-g sample size. In general, LC- MS/MS can detect compounds at concentrations approximately two orders of magnitude below the required action levels. Most of the com- pounds on the Oregon list are easily analyzed by LC-MS/MS in matrix, but some—such as the pyrethrins, cyfluthrin, and acequinocyl—require more careful method optimization of the chromatographic conditions to separate matrix interferences from the target analytes. These data demonstrate that LC-MS/MS methods can provide adequate sensitivity for the analysis of pesticides in cannabis samples.
JUNE/JULY 2017
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