Determination of Metals in Cannabis and Cannabis-related Samples using ICP-OES and ICP-MS

Significance of the Topic

Regulation of heavy metals in cannabis and related products has become essential for consumer safety and regulatory compliance. Diverse formulations—from raw plant material to concentrates and edibles—pose analytical challenges due to complex matrices. Sensitive, multi‐element methods are required to ensure that toxic elements such as cadmium, lead, arsenic, and mercury remain below prescribed action levels while allowing quantification of essential nutrients.

Objectives and Overview

This study evaluates the performance of microwave‐assisted acid digestion combined with two inductively coupled plasma techniques—optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS)—for the determination of macro‐ and trace elements in cannabis plant samples. Key aims include method validation using certified reference materials, assessment of calibration, limits of detection, and spike‐recovery performance, and demonstration on real cannabis samples.

Methodology and Instrumentation

Sample Preparation:

• Approximately 0.15 g of cannabis buds were digested in a single‐step microwave program (ramp to 240 °C over 20 min, hold 15 min) using 4 mL HNO₃ and 1 mL HCl.
• Digests were diluted with 1 % HNO₃ and 0.5 % HCl prior to analysis.

Instrumentation:

• ICP-MS: Agilent 7800 with High Matrix Introduction system, helium collision cell, micromist nebulizer, quartz torch and HMI; operated in helium mode for all elements.
• ICP-OES: Agilent 5110 SVDV with Advanced Valve System, SeaSpray nebulizer, double‐pass cyclonic spray chamber; axial viewing.

Operating parameters (RF power, gas flows, sampling depth) were auto‐optimized for robust performance.

Main Results and Discussion

Calibration and Sensitivity:

• Excellent linearity (R² ≥ 0.9994) for As, Cd, Pb, Hg by both techniques across ppb to ppm levels.
• Detection limits in the low ppb range for ICP-OES and sub‐ppb for ICP-MS.

Reference Material Validation:

• Analysis of NIST 1547 (Peach Leaves) and 1573a (Tomato Leaves) yielded recoveries of 90–120 % for certified elements, demonstrating complete digestion and accurate quantification.

Real Sample Analysis:

• Two cannabis samples showed As ~160 ppb, Cd ~11 ppb, Pb 24–55 ppb, Co ~143–162 ppb, all below regulatory limits.
• Spike recoveries for toxic metals were within ±20 % for both ICP-OES and ICP-MS methods.

Technique Comparison:

• ICP-OES offers lower capital cost and ease of use for macroelements and mid‐level trace metals.
• ICP-MS provides superior sensitivity for ultratrace analytes and broader dynamic range.

Benefits and Practical Applications

The validated protocols enable rapid, high‐throughput multi‐element screening of cannabis and derivatives for routine QC and safety testing. Laboratories can select ICP-OES for cost‐effective monitoring of major and mid‐level elements, while ICP-MS is recommended when ultralow detection limits are required.

Future Trends and Applications

As regulations evolve, demand will grow for simultaneous monitoring of additional elements and contaminants. Future work may focus on speciation analysis, coupling with chromatography for organic contaminants, further automation of sample prep, and integration of hyphenated techniques to expand analytical scope.

Conclusion

Microwave‐assisted acid digestion coupled with ICP-OES and ICP-MS provides accurate, precise, and sensitive multi‐element analysis for a variety of cannabis matrices. Both techniques meet quality control criteria and support compliance with current and future regulatory requirements.

References

1. A. Filipiak‐Szok, M. Kurzawa, M. Cichosz, and E. Szłyk, Anal. Lett. 48(16), 2627–2637 (2015)
2. National Conference of State Legislatures, NCSL, State Medical Marijuana Laws
3. L. Rough, Leafly’s State-by-State Guide to Cannabis Testing Regulations
4. P.J. Gray, W.R. Mindak, and J. Cheng, Elemental Analysis Manual for Food and Related Products, FDA (2015)