Determination of Pesticide Residues in Marijuana and Tea by QuEChERS and LC–MS–MS

Xiaoyan Wang, UCT, LLC

This application note outlines a simple method for the rapid determination of pesticide residues in marijuana and tea leaves. Dry samples are hydrated with water followed by QuEChERS extraction and dispersive solid-phase extraction (dSPE) cleanup using UCT's ChloroFiltr®, a specially designed sorbent to selectively remove chlorophyll without affecting the recovery of planar pesticides which can occur when carbon is used for dSPE cleanup. Chlorophyll removal is important as it can adversely impact gas chromatographic (GC) or liquid chromatographic (LC) injector and detection systems.

Extraction and Cleanup Materials

QuEChERS Extraction

1) Weigh 2 g of homogenized tea or marijuana sample into 50 mL centrifuge tubes (RFV0050CT).

2) Hydrate the samples by adding 10 mL of reagent water to the tubes and mix at a low speed for 1 h with a horizontal shaker.

3) Add internal standard to all samples.

4) For fortified samples, add appropriate volumes of pesticide standard solution.

5) Add 10 mL of acetonitrile and vortex for 1 min.

6) Add contents of Mylar pouch (ECQUUS2-MP) to each tube and shake vigorously for 1 min.

7) Centrifuge the samples at 3830 rcf for 5 min.

Figure 1: Extracts (a) before and (b) after dSPE cleanup.

dSPE Cleanup

1) Transfer 1 mL supernatant into a 2-mL dSPE tube (CUMPSGG2CT).

2) Vortex for 30 s.

3) Centrifuge at 15,300 rcf for 5 min.

4) Transfer 0.3 mL of the purified extract into a 2-mL auto-sampler vial.

5) Add 0.3 mL of reagent water, vortex, and then filter using a 0.45 μm syringe filter.

6) The samples are ready for LC–MS–MS analysis.

Table 1: Accuracy and precision data for fortified tea samples.

Conclusion

As described, this is a simple, fast, and cost-effective method for the determination of pesticide residues in tea and marijuana samples. After hydrating the samples, pesticide residues were extracted using a non-buffered QuEChERS approach, followed by dSPE cleanup using MgSO₄ for water removal; primary secondary amine (PSA) for removing organic acids, sugars, and some pigments; and ChloroFiltr® to selectively remove chlorophyll. The result is a clean extract for LC–MS–MS analysis. Good accuracy and precision were obtained using this method.

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