LC–MS/MS with ESI and APCI Sources for Meeting California Cannabis Pesticide and Mycotoxin Residue Regulatory Requirements

Sep 21, 2018
Abstract / Synopsis: 

Two different liquid chromatography–tandem mass spectrometry (LC–MS/MS) methods with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) were used for low-level analysis of 72 pesticides (including the very hydrophobic and chlorinated pesticides analyzed by gas chromatography [GC]–MS) in cannabis. The ability to screen and quantitate all 72 pesticides, including the very hydrophobic and chlorinated GC–MS amenable pesticides, in cannabis with only LC–MS/MS with ESI and APCI makes this approach a novel way of screening and quantitation of pesticides in cannabis and different matrices with a single instrument.

More than half of the United States has legalized the use of medical cannabis because of its therapeutic benefits for ailments such as cancer, multiple sclerosis, and amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease) (1–3). Like traditional agriculture crops, pesticides are sometimes used in cannabis cultivation to protect plants from pests and improve growth yield. Chronic exposure to pesticides can pose serious health risks; therefore, pesticide analysis in cannabis is an important consumer safety topic. Recent news has reported an alarming percentage of cannabis products to be tainted by high levels of pesticide residue, prompting recalls and public-safety alerts. Banned pesticides such as myclobutanil, imidacloprid, abamectin, etoxazole, and spiromesifen have been detected as residues on cannabis flowers and concentrated further in extracts and edibles. In Colorado, 20,000 packages of cannabis flowers in October 2015 were recalled because of pesticide contamination, and in November 2016, Oregon officials issued a health alert for specific batches of cannabis. Moreover, many of today’s cannabis products are inhaled after combustion, so there is growing concern among consumers and regulators because of the unknown effects of pesticide compounds when they are inhaled (4,5). The growing conditions for cannabis are also conducive to the growth of molds and fungi, which can produce carcinogenic mycotoxins including ochratoxin A and aflatoxins. As a result, testing for the levels of pesticide and mycotoxins in cannabis is important to ensure consumer safety and quality control.

High performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) has emerged as the method of choice for pesticide and mycotoxin analysis because it offers superior selectivity, sensitivity, ruggedness, and does not require extensive sample preparation before analysis. Although gas chromatography–tandem mass spectrometry (GC–MS/MS) methods have been developed for pesticide analysis in cannabis samples, they are only applicable to a smaller subset number of analytes. Compounds such as daminozide, a highly polar compound, and abamectin, a high-molecular-weight compound, are not amenable to analysis by GC–MS/MS because they are heat labile and degrade in either the GC injection port or the column at high temperature. GC–MS/MS methods are not as robust as LC–MS/MS methods for pesticide analysis in complex matrices because they require extensive sample preparation to prevent GC injection port contamination from complex matrices (6,7).

Because there is no federal guidance for the analysis of pesticides in cannabis samples, different states in the United States have developed their own testing guidelines. Oregon was the first state to come up with comprehensive guidelines for pesticide residue analysis in cannabis (8) and set regulatory limits for 59 pesticides in cannabis. However, California has issued more stringent action limits for 66 pesticides (including all but one of those found on the Oregon state list, and eight more) and five mycotoxins residues in cannabis flower and edibles (9). Numerous reports for pesticide analysis in cannabis have been published but these studies have certain deficiencies (10–12). Most of these studies either do not achieve detection limits to meet the California state action limits or use time-consuming sample preparation methods (for example, QuEChERS [quick, easy, cheap, effective, rugged, and safe] with dispersive solid-phase extraction [dSPE]) with poor recoveries for some of the pesticides, which require use of both LC–MS/MS- and GC–MS/MS-based instruments for analysis of all the pesticides. This requirement increases cost, complexity, and turnaround time of analysis substantially. In this work, 66 pesticides (including very hydrophobic and chlorinated pesticides typically analyzed by GC–MS/MS) and five mycotoxins spiked in cannabis flower extracts were analyzed at levels well below the action limits specified by California. An LC–MS/MS instrument was used with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources and a simple solvent extraction method with excellent recoveries for all analytes in acceptable range of 70–120%.

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Avinash Dalmia and Jason P. Weisenseel are with PerkinElmer, Inc., in Shelton, Connecticut. Erasmus Cudjoe, Toby Astill, and Feng Qin are with PerkinElmer, Inc., in Woodbridge, Ontario, Canada. Jacob Jalali is with PerkinElmer, Inc., in San Jose, California. Molly Murphy is with SC Labs in Tigard, Oregon. Travis Ruthenberg is with SC Labs in Santa Cruz, California. Direct correspondence to: [email protected]

How to Cite This Article

A. Dalmia, E. Cudjoe, T. Astill, J. Jalali, J.P. Weisenseel, F. Qin, M. Murphy, and T. Ruthenberg, Cannabis Science and Technology 1(3), 38-50 (2018).