Analysis of Heavy Metals in e-Liquids using the Agilent 5110 ICP-OES

Significance of the Topic

Electronic cigarettes have become a popular alternative to conventional smoking, driven by public health concerns and regulatory developments worldwide. The shift toward e-liquids eliminates many combustion by-products of tobacco but introduces questions about trace heavy metal exposure. Regulatory bodies such as the EU, US FDA, and AFNOR have established limits for arsenic, cadmium, mercury, lead, and antimony in e-liquids to ensure consumer safety. Robust analytical methods are essential for routine compliance testing and quality assurance in this rapidly expanding market.

Objectives and Study Overview

This study aimed to develop and validate a straightforward, reliable routine method for quantifying five heavy metals (As, Cd, Hg, Pb, Sb) in e-liquids. The method was designed to meet the AFNOR XP D90-300-2 standard requirements, featuring matrix-matched calibration to reflect common e-liquid compositions of propylene glycol, vegetable glycerin, and ethanol.

Methodology and Instrumentation

Sample and Standard Preparation:

• A blank matrix (48.5% PG, 49.5% VG, 2% EtOH) was diluted fivefold in water.
• Calibration standards (0–200 µg/L) were prepared in the blank solution.
• E-liquid samples (100% glycerol and 50:50 PG:VG) were diluted 5× before analysis and spiked at 0.5 mg/L for recovery tests.

Instrument and Operating Conditions:

• Agilent 5110 Vertical Dual View ICP-OES with SPS 3 autosampler
• SeaSpray nebulizer, cyclonic spray chamber, 1.8 mm injector torch
• Axial viewing mode, RF power 1.2 kW, plasma flow 12 L/min, auxiliary flow 1 L/min
• Internal standard: 1 mg/L scandium added to all solutions

Background Correction:
Complex carbon-based backgrounds from PG and VG were addressed using the fast automated curve-fitting technique (FACT) in ICP Expert software. FACT models blank and analyte spectra, deconvolutes interferences, and improves detection limits without extending analysis time.

Main Results and Discussion

Calibration Performance:

• Linear response from 0 to 200 µg/L for all five elements (R² > 0.9997).

Detection and Quantification Limits:

• Method LOQs in 1/5 diluted solution ranged from 0.0002 mg/L (Cd) to 0.014 mg/L (As), well below AFNOR maximum limits.

Precision and Accuracy:

• Repeatability tested at 50 µg/L: RSD < 3.5% for all elements.
• Spike recoveries between 90% and 107%.

Sample Analysis:

• Unspiked e-liquid samples showed heavy metals below LOQ.
• Spiked recoveries in two e-liquid formulations confirmed method robustness across different matrices.

FACT deconvolution effectively separated analyte peaks from carbon-related interferences, enhancing signal accuracy and lowering quantitation limits by an order of magnitude compared to off-peak correction.

Benefits and Practical Applications

The described ICP-OES method offers rapid, reliable routine testing for heavy metals in e-liquids. Key advantages include:

• Minimal sample preparation with matrix-matched calibration.
• High sensitivity and low LOQs through FACT background correction.
• Excellent precision and accuracy across common e-liquid formulations.
• Compliance with international quality and safety standards (AFNOR, EU, FDA).

This approach supports regulatory monitoring, product development, and consumer safety assessments in tobacco and vaping industries.

Future Trends and Applications

Emerging directions in heavy metal analysis of e-liquids and related matrices may include:

• Integration of automated sample preparation for higher throughput.
• Adoption of tandem mass spectrometry (ICP-MS) for ultratrace analyses.
• Expansion to other product matrices such as aerosols and device residues.
• Data analytics and machine learning for spectral deconvolution and trend monitoring.

These advances will further enhance sensitivity, reduce turnaround times, and broaden the scope of contaminants monitored in vaping products.

Conclusion

The Agilent 5110 VDV ICP-OES method with FACT background correction delivers a robust solution for routine quantification of As, Cd, Hg, Pb, and Sb in e-liquids. It offers low detection limits, strong linearity, and reliable performance across diverse sample matrices, fulfilling AFNOR and regulatory standards for consumer safety testing.

References

1. World Health Organization. Tobacco Fact Sheet; 2018.
2. Zhu SH, Sun JY, Bonnevie E, et al. Four Hundred and Sixty Brands of E-Cigarettes and Counting: Implications for Product Regulation. Tobacco Control. 2014;23(Suppl 3):iii3–iii9.
3. European Union. Tobacco Products Directive 2014/40/EU; 2014.
4. US Food and Drug Administration. FDA’s Deeming Rule for Tobacco Products; 2016.
5. AFNOR. XP D90-300-2: Electronic Cigarettes and E-Liquids—Part 2: Requirements and Test Methods; 2016.
6. Agilent Technologies. Real-Time Spectral Correction Using FACT; 2016.