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Analysis of Pesticides in a Cannabis sativa Matrix

INTRODUCTION

Cannabis sativa is well-known for its use as a recreational drug due the presence of the psychoactive compound tetrahydrocannabinol (THC), and has been listed as a Schedule 1 drug in the United States since the passage of the Controlled Substances Act of 1970.1 With the recent surge in legalization of recreational and medicinal use, there is a need for reliable analytical tools to meet the regulatory requirements for pesticide testing in Cannabis. Action limits for each pesticide vary between jurisdictions, but can be as low as 10 ppb.2,3
The JEOL JMS-TQ4000GC triple-quadrupole GC-MS/MS system offers high speed and high sensitivity for quantitation of trace or residual pesticides. The TQ4000 combines a unique short collision cell with JEOL’s patented ion accumulation and timed detection technology to provide high sensitivity and selectivity, as well as the fastest selected reaction monitoring (SRM) switching speed available (up to 1000 transitions per second).

JEOL msPrimo and Escrime software provide all of the tools needed to develop optimized methods for target compound quantitation and report generation. In this application note, we describe a sensitive method for analyzing pesticides in Cannabis sativa matrix using the SRM capabilities of our triple quadrupole system.

EXPERIMENTAL

Dried Cannabis sativa flower buds for recreational use were purchased from a local dispensary. Approximately 1 gram of flower was extracted into 10 mL of 90:10 acetonitrile:dimethylacetamide by sonication for 15 minutes. The extract was centrifuged at approximately 2500 rpm for 10 minutes, followed by 10X dilution. One mL of the diluted extract was put through a dSPE cleanup step using Restek Q-sep QuEChERS dSPE Tubes (AOAC 2007.01 method4, PN# 26125) and following the provided dSPE instructions. The supernatant was used as the matrix for each sample. Each spiked sample was created by adding 10 μL of prepared pesticide standard to 90 μL of the matrix. Samples were analyzed on the JMS-TQ4000GC using the parameters and SRM channels outlined in Tables 1 - 3 below. Optimal product- and precursor-ion pairs and optimized collision energies for each pesticide were determined using built-in SRM optimization tools. Each sample was run in triplicate with the exception of the 1 ppb samples for which 8 replicates were done to calculate the instrument detection limit (IDL) where possible.

RESULTS

Figure 1 shows the total ion current chromatogram (TICC) with labeled peaks, and Figure 2 shows several selected SRM chromatograms.  Table 4 lists the data acquired for 46 pesticides analyzed by GC-MS/MS analysis. There were 41 pesticides observed at 1 ppb or less, which translates to 10 ppb on the plant. The IDL and %CV were not calculated for samples that could not be observed at 1 ppb.  For samples with isomers (e.g., chlordane), the best performing isomer was used for reporting.  All samples below showed good linearity, even up to 100 ppb.  Example calibration curves are shown in Figure 3.  Although some matrix effects were observed, system performance was generally good with very few pesticides affected by matrix interference.

CONCLUSIONS

The JMS-TQ4000GC is an excellent platform for fast, sensitive analysis of a wide range of pesticides in Cannabis matrix. Using built-in SRM optimization tools, optimal ion transitions and collision energies for each pesticide were determined in the presence of the matrix. The SRM method provided high sensitivity and selectivity, and reduced matrix effects without a complicated extraction method.  Forty-one pesticides were observed at one ppb or lower with good linearity, which translates to ten ppb on the flower and is sufficient to meet the action limits of jurisdictions of interest. 

REFERENCES

  1. United States Drug Enforcement Administration. The Controlled Substances Act https://www.dea.gov/controlled-substances-act (accessed Mar 19, 2020).
  2. Health Canada. Mandatory cannabis testing for pesticide active ingredients - List and limits https://www.canada.ca/en/public-health/services/publications/drugs-health-products/cannabis-testing-pesticide-list-limits.html (accessed Mar 19, 2020).
  3. Dodson, L.; Laprade, N. M. The Natalie M. Laprade Maryland Medical Cannabis Commission’s (MMCC) Technical Authority for Medical Cannabis Testing; 2019.
  4. Official Methods of Analysis. Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate. Association of Official Agricultural Chemists: 2007.01.

Table 1. Gas Chromatograph parameters.

GC 7890B (Agilent)
Column ZB-5MSPlus, 30.0 m, 0.25 mm i.d., 0.25 µm
(Phenomenex, Cat#:7HG-G030-11)
Inlet liner Zebron Plus 4 mm Single Taper w/Wool on bottom
(Phenomenex Cat#: AG2-0A11-05)
Inlet Temp. 260°C
Carrier Gas Type, Flow He, 1.000 mL/min constant flow
Mode Pulsed Splitless
Pulsed Pressure, Time 206.84 kPa, 0.550 min
Purge Flow 30 mL/min, 1.0 min
Septum Purge Flow 3.0 mL/min
Saver flow, Time 15 mL/min, 5.0 min
Injection Volume 1.0 µL
Oven Program 80°C (0.75 min) → 35°C/min → 190°C → 5°C/min →
240°C → 20°C/min → 300°C (6 min)

Table 2. Mass Spectrometer parameters.

JMS-TQ4000GC
Ion Source Temp. 250°C
Interface Temp. 300°C
Ionization Mode EI+, 70 eV, 100 µA
Measurement Mode SRM, High Sensitivity
Target Cycle Time Approx. 330 ms
Acquisition Rate 2.778 Hz
Channel Time 20 – 100 ms
Relative EM Voltage 900 V
Collision Gas N2, 10%

Table 3. SRM channel data.

Compound Quantitative ion Referenced ion 1 Referenced ion 2 Collision Energy
Precursor Product ion Precursor Product ion Precursor Product ion Quantitative ion Referenced ion 1 Referenced ion 2
ion m/z m/z ion m/z m/z ion m/z m/z
Acephate 136 94 136 42 77 51 10 15 15
Azoxystrobin 344 156 388 345 388 360 30 20 10
Bifenazate 258 196 258 199 300 196 15 10 25
Bifenthrin 181 165 181 166 181 164 30 20 30
Boscalid 140 112 140 76 342 140 10 25 20
Carbaril (decomp) 144 115 144 116 89 63 25 15 15
Carbaril (intact) 144 115 144 116 89 63 25 15 15
Carbofuran 164 149 164 103 149 103 15 25 20
Chlordane (cis) 375 266 373 266 373 264 20 25 25
Chlordane (trans) 373 266 373 264 375 266 25 20 20
Chlorfenapyr 59 31 247 227 59 41 5 15 5
Chlorpyrifos 197 169 199 171 197 134 15 15 25
Chlorpyrifos-d10 200 172 260 167 260 139 20 25 30
Cinerin I 150 108 123 79 123 81 10 20 10
Cinerin II 107 91 121 93 121 77 10 5 25
Clofentezine 137 102 137 75 139 102 10 25 15
Cyfluthrin I 226 206 206 151 206 150 15 25 25
Cyfluthrin II 226 206 163 127 163 91 20 10 15
Cyfluthrin III 226 206 163 127 163 91 20 10 15
Cyfluthrin IV 226 206 163 127 163 91 15 10 15
Cypermethrin I 163 127 181 152 163 91 10 25 20
Cypermethrin II 163 127 181 152 163 91 10 25 15
Cypermethrin III 163 127 181 152 163 91 10 25 15
Cypermethrin IV 163 127 181 152 163 91 10 25 15
Diazinone 137 84 199 135 199 93 15 10 15
Dichlorvos 109 79 185 93 79 47 10 15 10
Dimethoate 93 63 87 42 87 46 10 10 20
Ethoprophos 158 97 158 114 97 79 15 10 20
Etofenprox 163 107 163 135 135 107 20 10 10
Etoxazole 141 113 300 270 204 176 15 30 10
Fenoxycarb 116 88 186 157 186 158 10 15 10
Fipronil 213 143 367 213 213 178 25 30 20
Fludioxonil 248 127 248 154 248 182 30 25 20
Imazalil 173 145 215 173 173 109 20 10 25
Jasmolin I 164 109 123 79 123 81 10 20 10
Jasmolin II 121 93 121 77 121 91 10 20 20
Kresoxim-methyl 116 89 206 116 206 131 20 10 10
Malathion 127 99 93 63 125 79 10 10 15
Metalaxyl 206 132 132 117 206 105 20 15 20
Methiocarb 168 153 168 109 153 109 10 15 10
Methomyl 105 88 58 31 105 58 5 5 10
Methyl parathion 263 109 125 79 125 47 15 10 15
MGK 264 I 164 93 164 121 164 77 15 10 30
MGK 264 II 164 67 164 80 164 98 10 25 15
Myclobutanil 179 125 150 123 179 90 20 20 30
Naled 145 109 185 93 145 113 10 15 20
Oxamyl 98 58 98 69 72 56 10 5 10
Paclobutrazol 236 125 125 89 236 132 20 25 20
Permethrin (cis) 183 153 183 168 183 165 20 20 20
Permethrin (trans) 183 153 183 168 163 91 20 20 15
Phosmet 160 133 160 105 160 77 15 20 20
Piperonyl butoxide 176 117 176 103 176 131 20 25 15
Prallethrin 123 81 123 79 105 77 10 20 15
Propiconazole I 173 109 173 145 259 191 25 15 10
Propiconazole II 173 109 173 145 259 191 25 15 10
Propoxur 110 63 152 110 110 64 25 10 20
Pyrethrin II 133 105 91 65 107 91 10 15 10
Pyridaben 147 117 147 105 147 132 20 10 15
Spiromesifen 272 254 272 209 272 226 5 15 10
Spiroxamine I 100 72 100 58 100 41 10 10 20
Spiroxamine II 100 72 100 58 100 41 10 10 20
Tebuconazole 250 125 125 89 125 99 25 20 20
Thiamethoxam 132 71 212 139 212 182 10 15 5
Trifloxystrobin 116 89 172 145 131 89 20 20 25

Figure 1. TIC chromatogram.

Figure 2. Selected SRM chromatograms.

Figure 3. Selected calibrations curves.

Table 4. Performance data for tested pesticides.

Compound Range (ppb) Linearity (R^2) % CV LOQ (ppb) IDL (ppb)
Azoxystrobin 0.5 - 100 0.9809 12.50 1 0.37
Bifenazate 0.5 - 100 0.9815 12.18 1 0.37
Bifenthrin 0.25 - 100 0.9928 8.37 0.5 0.25
Boscalid 0.25 - 100 0.9902 4.77 0.5 0.14
Carbaril 0.5 - 100 0.9952 8.10 10 0.24
Carbofuran 0.5 - 100 0.9953 8.57 0.5 0.26
Chlordane 1 - 100 0.9974 18.13 1 0.54
Chlorfenapyr 0.5 - 100 0.9932 13.87 1 0.42
Chlorpyrifos 0.25 - 100 0.9981 8.72 0.5 0.26
Chlorpyrifos-d10 1 - 100 0.9967 16.81 2.5 0.5
Cinerin I 25 - 100 0.9844 N/A 25 N/A
Clofentezine 0.5 - 100 0.9992 6.46 1 0.19
Cyfluthrin 0.5 - 100 0.9963 6.76 0.5 0.2
Cypermethrin 1 - 100 0.9954 6.68 2.5 0.2
Diazinone 0.25 - 100 0.9978 9.22 0.5 0.28
Dichlorvos 0.25 - 100 0.9929 9.28 0.5 0.28
Dimethoate 1 - 100 0.9918 8.10 2.5 0.24
Ethoprophos 0.25 - 100 0.9921 8.77 1 0.26
Etofenprox 0.25 - 100 0.9901 5.18 2.5 0.16
Etoxazole 0.5 - 100 0.9957 7.74 0.5 0.23
Fenoxycarb 0.5 - 100 0.9944 10.05 5 0.3
Fipronil 0.5 - 100 0.9929 10.20 1 0.31
Fludioxonil 0.25 - 100 0.9936 10.46 0.5 0.31
Imazalil 1 - 100 0.9787 20.72 1 0.62
Jasmolin I 2.5 - 100 0.9937 N/A 25 N/A
Kresoxim-methyl 0.5 - 100 0.9975 9.49 0.5 0.28
Malathion 0.25 - 100 0.9961 8.78 2.5 0.26
Metalaxyl 0.5 - 100 0.9975 7.90 2.5 0.24
Methiocarb 1 - 100 0.9957 12.35 1 0.37
Methomyl 0.25 - 100 0.9763 24.74 0.5 0.74
Methyl parathion 0.5 - 100 0.9948 10.82 2.5 0.32
MGK 264 0.5 - 100 0.9972 5.21 0.5 0.16
Myclobutanil 0.25 - 100 0.9923 9.30 0.5 0.28
Naled 25 - 100 N/A N/A 50 N/A
Paclobutrazol 0.25 - 100 0.9953 14.15 0.5 0.42
Permethrin 2.5 - 100 0.9946 N/A 2.5 N/A
Phosmet 0.5 - 100 0.9948 8.49 0.5 0.25
Prallethrin 10 -100 0.9952 N/A 25 N/A
Propiconazole 0.5 - 100 0.9944 8.70 0.5 0.26
Propoxur 0.25 - 100 0.9955 9.67 0.5 0.29
Pyridaben 0.5 - 100 0.9952 6.66 1 0.2
Spiromesifen 0.25 - 100 0.9934 4.98 0.5 0.15
Spiroxamine 0.25 - 100 0.9985 7.07 2.5 0.21
Tebuconazole 0.5 - 100 0.9934 9.93 0.5 0.3
Thiamethoxam 1 - 100 0.9951 9.59 1 0.29
Trifloxystrobin 0.5 - 100 0.9972 6.59 1 0.2

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