ABSTRACT
BACKGROUND: Cannabis sativa L. also known as industrial hemp, is primarily cultivated as source material for cannabinoids cannabidiol (CBD) and ∆9-tetrahydrocannabinol (∆9-THC). Pesticide contamination during plant growth is a common issue in the cannabis industry which can render plant biomass and products made from contaminated material unusable. Remediation strategies to ensure safety compliance are vital to the industry, and special consideration should be given to methods that are non-destructive to concomitant cannabinoids. Preparative liquid chromatography (PLC) is an attractive strategy for remediating pesticide contaminants while also facilitating targeted isolation cannabinoids in cannabis biomass. METHODS: The present study evaluated the benchtop-scale suitability of pesticide remediation by liquid chromatographic eluent fractionation, by comparing retention times of 11 pesticides relative to 26 cannabinoids. The ten pesticides evaluated for retention times are clothianidin, imidacloprid, piperonyl butoxide, pyrethrins (I/II mixture), diuron, permethrin, boscalid, carbaryl, spinosyn A, and myclobutanil. Analytes were separated prior to quantification on an Agilent Infinity II 1260 high performance liquid chromatography with diode array detection (HPLC-DAD). The detection wavelengths used were 208, 220, 230, and 240 nm. Primary studies were performed using an Agilent InfinityLab Poroshell 120 EC-C18 3.0 × 50 mm column with 2.7 µm particle diameter, using a binary gradient. Preliminary studies on Phenomenex Luna 10 µm C18 PREP stationary phase were performed using a 150 × 4.6 mm column. RESULTS: The retention times of standards and cannabis matrices were evaluated. The matrices used were raw cannabis flower, ethanol crude extract, CO2 crude extract, distillate, distillation mother liquors, and distillation bottoms. The pesticides clothianidin, imidacloprid, carbaryl, diuron, spinosyn A, and myclobutanil eluted in the first 3.6 min, and all cannabinoids (except for 7-OH-CBD) eluted in the final 12.6 min of the 19-minute gradient for all matrices evaluated. The elution times of 7-OH-CBD and boscalid were 3.44 and 3.55 min, respectively. DISCUSSION: 7-OH-CBD is a metabolite of CBD and was not observed in the cannabis matrices evaluated. Thus, the present method is suitable for separating 7/11 pesticides and 25/26 cannabinoids tested in the six cannabis matrices tested. 7-OH-CBD, pyrethrins I and II (RTA: 6.8 min, RTB: 10.5 min), permethrin (RTA: 11.9 min, RTB: 12.2 min), and piperonyl butoxide (RTA: 8.3 min, RTB: 11.7 min), will require additional fractionation or purification steps. CONCLUSIONS: The benchtop method was demonstrated have congruent elution profiles using preparative-scale stationary phase. The resolution of pesticides from cannabinoids in this method indicates that eluent fractionation is a highly attractive industrial solution for pesticide remediation of contaminated cannabis materials and targeted isolation of cannabinoids.
ABSTRACT
Cannabinoids are important industrial analytes commonly assayed with high-pressure liquid chromatography (HPLC). In this study, we evaluate the suitability of MIL-53(Al), a commercially available metal-organic framework (MOF), as a stationary phase for cannabinoid separations. The suitability of an MOF for a given separation is hypothesized to be limited by the ability of a given molecule to enter the pore of the MOF. To evaluate the extent of possible adsorptive interactions between cannabinoids and the interior surface area of MIL-53(Al), the radii of gyration (Rg) and solvent-accessible surface areas were calculated for three cannabinoids, namely, cannabidiol, cannabinol, and Δ9-tetrahydrocannabinol, as well as the MOF. These values were used to calculate the theoretical adsorption capacity of the MOF, using four competing adsorption models. The Rg of cannabinoids (4.1 Å) is larger than one MOF pore aperture dimension (4.0 × 5.0 Å). The adsorption capacity was measured by relating a decrease in the cannabinoid concentration in acetonitrile when exposed to 100 mg of MOF. The cannabinoid uptake by the MOF was estimated using the relative standard deviation (RSD) of the soaking solution assay, as the decomposition-corrected RSD as uptake (DCRU). The DCRU was calculated as 0.007 ± 0.004 µgcannabinoids/mgMOF. These findings indicate that most of the MOF surface area was inaccessible for adsorption by cannabinoids due to size-exclusion effects. The implication of this work is that the suitability of an MOF for adsorptive separations, such as liquid chromatography, must have an upper limit for the size of the analyte. Additionally, MOFs may generally be more suitable for separations in the gas phase, where adsorbates are not hindered by the presence of a solvation shell.
