Accurate Analysis of Trace Mercury in Cosmetics using the Agilent 8900 ICP-QQQ

Significance of the topic

Mercury compounds are highly toxic and may be absorbed through the skin, posing serious health risks. Regulatory agencies restrict mercury in cosmetics, but “anti-aging” and skin-lightening products have been found to contain trace levels of mercury. Accurate quantification at sub-ppb levels is challenging due to low ionization efficiency of Hg and severe polyatomic interferences from tungsten oxide and hydroxide in tungsten-rich matrices.

Objectives and Study Overview

This application note evaluates the performance of the Agilent 8900 triple-quadrupole ICP-MS (ICP-QQQ) for reliable trace-level mercury determination in a cosmetic lotion containing high tungsten. The study compares no-gas, He collision, O₂ single-quadrupole, and O₂ MS/MS modes to assess interference removal and quantification accuracy across five major Hg isotopes.

Methodology and Instrumentation

Sample Preparation:

• Tungsten-rich cosmetic lotion (~4000 mg/kg W) was diluted 100× in deionized water with 0.5 % HCl to stabilize Hg.
• Hg standards prepared in 0.5 % high-purity HCl.

Instrumentation:

• Agilent 8900 ICP-QQQ with glass concentric nebulizer, quartz spray chamber, quartz torch, Ni cones.
• Operating modes: no gas, He cell gas, O₂ cell gas in SQ mode, and O₂ cell gas in MS/MS mode.
• Key conditions: RF power 1550 W, sampling depth 8 mm, carrier gas 0.8 L/min, He 5 mL/min, O₂ 0.9 mL/min.

MS/MS Reaction Mechanism:
Q1 set to target isotope mass (e.g., m/z 200) allows only Hg⁺ and WO⁺ into the cell. In O₂, WO⁺ converts to WO₂⁺/WO₃⁺ (higher m/z), while Hg⁺ remains. Q2 at the original m/z transmits interference-free Hg to the detector.

Key Results and Discussion

Calibration and Figures of Merit:

• Preferred isotope 202Hg showed linearity (R ≈ 0.999), DL ~ 0.002 μg/L and BEC ~ 0.003 μg/L in O₂ MS/MS mode.

Isotope Ratio Accuracy:

• Comparison of measured vs. natural isotope ratios in W-spiked samples showed only O₂ MS/MS matched theoretical values, confirming effective WO⁺/WOH⁺ removal across 198–202Hg.

Quantitative Results in Cosmetic Sample:

• No-gas, He, and O₂ SQ modes produced grossly inflated Hg due to interferences (up to tens of thousands μg/kg).
• O₂ MS/MS yielded consistent results (~2 μg/kg in original lotion) for all five isotopes after 100× dilution.

Spike Recovery:

• 30 ppt spike of 200Hg in the diluted matrix gave 104 % recovery in O₂ MS/MS mode, demonstrating excellent matrix tolerance.

Benefits and Practical Applications

• Reliable trace-level Hg determination in tungsten-rich cosmetics and other complex matrices
• On-mass MS/MS approach avoids mass-shift methods, simplifying method development
• Multiple isotope confirmation supports regulatory and QA/QC requirements

Future Trends and Opportunities

Emerging applications of ICP-QQQ include speciation analysis of mercury, coupling with automated sample introduction for high throughput, and expanding to other challenging matrices (e.g., mining byproducts, environmental sediments). Advances in reaction gas chemistry may further enhance interference control for a broader range of elements.

Conclusion

The Agilent 8900 ICP-QQQ with O₂ MS/MS mode provides robust removal of tungsten-based polyatomic interferences, enabling accurate and precise trace mercury analysis in cosmetics. The method meets stringent regulatory requirements and offers reliable multi-isotope confirmation for QA/QC.

References

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2. Federal Food, Drug, and Cosmetic Act (FD&C Act), Cosmetics and U.S. Law, FDA, accessed October 2018.
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4. L. Fu, S. Shi, and X. Chen, Food Chemistry, 2018, 245, 692–697.
5. L. Whitty-Léveillé, K. Turgeon, C. Bazin, and D. Larivière, Anal. Chim. Acta, 2017, 961, 33–41.