Determination of Heavy Metals in Cannabis and Hemp Products Following AOAC Method for ICP-MS

Importance of the Topic

Cannabis and hemp products can accumulate toxic heavy metals such as arsenic, cadmium, mercury, and lead from soil and water. Regulatory agencies set strict limits for these contaminants to protect consumer health. A standardized, robust analytical method is essential to ensure product safety, enable regulatory compliance, and build consumer trust.

Objectives and Study Overview

This study evaluates the AOAC First Action ICP-MS method for determining As, Cd, Hg, Pb, and optional elements in a broad range of cannabis matrices. Using an Agilent 7850 ICP-MS with Ultra High Matrix Introduction (UHMI) and ORS4 collision cell, the work demonstrates method linearity, limits of quantitation, accuracy with reference materials, and spike recovery in real samples.

Methodology and Used Instrumentation

Sample Preparation and Microwave Digestion:

• Homogenized plant and product samples (~0.5 g) digested in 9 mL HNO3 and 1 mL HCl using a CEM MARS 6 microwave system in TFM vessels.
• Digests diluted to 50 mL with reagent water (100× dilution).
• Four NIST plant SRMs processed identically to verify digestion completeness and method accuracy.

ICP-MS Analysis:

• Agilent 7850 ICP-MS with UHMI for automated aerosol dilution (4×) and ORS4 He collision mode for KED interference removal.
• MicroMist glass concentric nebulizer, quartz spray chamber, quartz torch, nickel cones, Agilent SPS 4 autosampler.
• Calibration in 1% HNO3/0.5% HCl: Hg 0.01–10 ppb; other elements 0.1–100 ppb.
• IntelliQuant full-mass semiquantitative screening concurrent with quantitative runs.

Main Results and Discussion

Calibration and Sensitivity:

• Excellent linearity (R=1.0000) for As, Cd, Hg, Pb; detection limits ≤0.016 ppb.
• Limits of quantitation ≤10 ppb in original samples, meeting AOAC SMPR.

Accuracy and Recoveries:

• NIST SRMs returned 80–120% recoveries for target elements.
• Spike recoveries in fortified blanks: 98–117% across all SMPR elements and spike levels.
• Spike recoveries in four cannabis product types ranged 64–114%, meeting AOAC criteria (60–115% low, 80–115% medium/high).

Interference Management:

• He KED mode and half-mass correction effectively removed rare earth doubly charged overlaps at m/z 75 and 78.

Benefits and Practical Applications of the Method

• Versatile analysis across diverse cannabis and hemp matrices without matrix-matched calibration.
• High throughput with automated UHMI, minimal instrument adjustment between sample types.
• Concurrent semiquantitative screening of 78 elements via IntelliQuant, aiding method development and troubleshooting.
• Compliance support for medicinal and recreational cannabis testing facilities.

Future Trends and Opportunities

• Expanded use of full-mass screening for emerging contaminants and nutritional elements.
• Integration of advanced collision/reaction cell chemistries for improved interference removal.
• Automation and high-throughput workflows including autosampler optimization and digital LIMS integration.
• Development of unified methods covering microplastics and nanoparticle contaminants in botanical products.

Conclusion

The AOAC First Action ICP-MS method run on the Agilent 7850 platform provides reliable, sensitive, and accurate heavy metal determination in cannabis and hemp products. The combination of microwave digestion, UHMI, ORS4 collision cell, and IntelliQuant screening delivers robust performance across varied matrices, ensuring regulatory compliance and consumer safety.

References

1. AOAC Expert Review Panel (ERP) for Chemical Contaminants in Cannabis Methods, August 2021 Analytical Methods Week Highlights.
2. Agilent IntelliQuant for ICP-MS, Agilent publication 5994-2796EN.
3. T. Kubota, Simplifying Correction of Doubly Charged Ion Interferences with Agilent ICP-MS MassHunter, Agilent publication 5994-1435EN.