Determination of cadmium, lead and mercury in cannabis flowers by microwave plasma atomic emission spectrometry.

BACKGROUND: The rapid expansion of legal medicinal and recreational cannabis markets has increased the need for quality control strategies and regulatory monitoring of contaminants in cannabis products. Toxic elements are of particular concern because cannabis plants can accumulate trace metals from environmental and cultivation sources. OBJECTIVE: To evaluate microwave plasma atomic emission spectrometry (MP AES) as a cost-effective alternative to conventional argon plasma-based techniques for the determination of cadmium (Cd), lead (Pb), and mercury (Hg) in cannabis flowers. METHODS: Samples were prepared by microwave-assisted acid digestion using nitric acid. Cd and Pb were determined sequentially by MP AES, while Hg was quantified using a dedicated cold vapor generation coupled to MP AES (CV-MP AES). The analytical methodologies were optimized and validated according to Eurachem guidelines. RESULTS: Limits of quantification were 0.40 µg/g for Cd, 0.18 µg/g for Pb, and 0.015 µg/g for Hg. Accuracy was evaluated using reference materials and spiked samples, with recoveries of 95-101% and 81-90%, respectively, and relative standard deviations below 15%. Good linearity was achieved (R² > 0.999). The methodologies were applied to 30 commercial cannabis flower samples, where Cd and Hg were not detected, and Pb was quantified at 2.12 ± 0.13 µg/g. CONCLUSIONS: MP AES and CV-MP AES provide adequate accuracy and precision for the determination of Cd, Pb, and Hg in cannabis flowers. The proposed methodologies represent a practical, cost-effective, and sustainable alternative to argon-based plasma techniques for routine quality control and compliance testing of cannabis products.