Marihuana safety: Potency of cannabinoids, pesticide residues, and mycotoxin in one analysis by LC/MS/MS

Abstract Because marihuana is legalized for both recreational and medical use state-by-state in the United States and throughout Canada, the governing bodies must assure its safety. Laws have been enacted to assure marihuana that is legally distributed does not contain harmful substances. Among them are pesticides and mycotoxins. Knowing the potency of a product is also a safety issue, as well as an economic one for both the distributor and the end user. A mould common to marihuana is Aspergillus which produces aflatoxins and ochratoxin. Safe levels for these are very low, whereas pesticide concentrations are higher. The compounds typically evaluated for potency are at the percent level. To analyse all three categories of compounds by the very sensitive technique of LC/MS/MS requires suppression of the signal for cannabinoids responsible for potency while maintaining sensitivity for the pesticides and mycotoxins. This is achieved by measuring the LC/MS/MS transitions of the C12 isotopes for pesticides and mycotoxins while using the lower intensity of the C13 isotope transitions for the cannabinoids. Limits of quantification for the aflatoxins are at 5 ppb whereas ochratoxin is at 20 ppb. The pesticide limits are generally at or below 100 ppb. Tetrahydrocannabinol (THC) and cannabidiol (CBD) LOQs are 0.1%. Calibration of the cannabinoids is done with low levels using the C12 isotope transition to reduce the cost of standards. Because the plant is a complex matrix, sample preparation includes a 250-fold dilution. How the calibration, sample preparation, and determination of these different categories of compounds with varied needs for sensitivity is described in detail.