WCPS: New Standardized Methods for Metals in Cannabis

Significance of the topic

Reliable analysis of toxic and essential metals in cannabis is critical for consumer safety, regulatory compliance and product quality control. The lack of official standardized methods has challenged laboratories tasked with ensuring that cannabis and derived products meet strict limits for arsenic, cadmium, mercury and lead. Adoption of validated approaches supports consistent results across testing facilities and fosters confidence in analytical data.

Objectives and study overview

This work presents the development and validation of new standardized ICP-MS methods for quantifying arsenic, cadmium, mercury and lead in a broad range of cannabis and hemp matrices. Methods were adopted by AOAC with First Action status in August 2021 and are under development as an ASTM standard. Key goals included demonstrating accuracy, precision and interference removal across diverse sample types.

Methodology and instrumentation used

Sample preparation and digestion

• Approximately 0.5 g of plant material or product weighed into TFM MARSXpressPlus vessels
• Addition of 9 mL HNO3 and 1 mL HCl
• Microwave digestion using CEM MARS 6 system

Instrumental analysis

• Agilent 7850 ICP-MS with Ultra High Matrix Introduction (UHMI) system and ORS4 collision/reaction cell
• Micro Mist glass concentric nebulizer and quartz spray chamber
• Quartz torch with 2.5 mm id injector, nickel-plated copper sampling and skimmer cones
• Agilent SPS 4 autosampler

Main results and discussion

Calibration and detection limits

• Excellent linearity for As, Cd, Hg and Pb across calibration ranges
• Limits of quantitation below 10 ppb in original sample, meeting AOAC SMPR criteria

Spike recovery and SRM evaluation

• Spike recoveries for As, Cd, Hg and Pb fell within 60–115 % at low spikes and 80–115 % at medium and high spikes across four cannabis samples
• Analysis of four NIST plant-based SRMs yielded mean recoveries between 80 and 120 % for certified elements, confirming digestion and measurement accuracy

Interference monitoring

• IntelliQuant data revealed presence of rare earth elements in cannabis matrices, which can form doubly charged interferences on Zn, As and Se
• Use of ORS4 cell in helium mode effectively removed polyatomic interferences

Benefits and practical applications

The validated ICP-MS method enables consistent quantification of priority toxic elements in inhaled, oral, topical and manufacturing cannabis products. Laboratories can adopt the AOAC and upcoming ASTM standard to meet regulatory requirements, support quality assurance and ensure product safety across the supply chain.

Future trends and potential applications

Further method development may include expansion to additional trace and rare elements, high-throughput automation, speciation studies and adaptation to emerging cannabis-derived consumables. Continued refinement of collision cell technologies and software algorithms will improve interference removal in complex botanical matrices.

Conclusion

The collaborative efforts between instrument manufacturers, AOAC ERP and ASTM led to the first official standardized ICP-MS methods for metals in cannabis. The Agilent 7850 ICP-MS with UHMI and ORS4 cell demonstrated robust performance, meeting stringent recovery and quantitation criteria. These methods establish a reliable analytical foundation for regulatory testing and quality control in the rapidly growing cannabis industry.

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