Measuring Multiple Elements in Nanoparticles using spICP-MS

Significance of the Topic

Single particle inductively coupled plasma mass spectrometry (spICP-MS) is an emerging analytical technique that delivers simultaneous information on particle size, number concentration, and elemental composition for nanoparticles (NPs) in complex matrices. Its rapid, sensitive measurements are critical for environmental monitoring, quality control in consumer products, and safety assessments of engineered nanomaterials.

Objectives and Study Overview

This work demonstrates a Rapid Multi-Element Nanoparticle Analysis mode, implemented in the Agilent ICP-MS MassHunter software, enabling sequential measurement of up to 16 elements in a single spICP-MS run. The main goals were:

• Verify method accuracy using reference materials (NIST 1898 TiO₂, NIST 8013 Au NPs).
• Apply the multi-element spICP-MS approach to characterize Al(OH)₃, TiO₂, and ZnO NPs in commercial sunscreens.
• Assess TiO₂ and ZnO NP levels in municipal swimming pool waters.

Methodology and Instrumentation

Samples were prepared by controlled dilution and sonication to achieve optimal NP dispersions. Commercial sunscreens (three brands with varying Al, Ti, Zn ingredients) were diluted in Triton™ X-100 and de-ionized water. Swimming pool waters (indoor and three outdoor pools) were collected without pretreatment.

Used Instrumentation

An Agilent 7900 ICP-MS equipped with:

• Glass concentric nebulizer and quartz spray chamber (2 °C).
• Quartz torch with 1.0 mm injector and nickel cones.
• Peristaltic pump (0.35 mL/min sample uptake).
• Time-Resolved Analysis mode (100 μs dwell time, no settling time).
• ICP-MS MassHunter Single Nanoparticle Application Module with Rapid Multi-Element Nanoparticle Analysis wizard.

Main Results and Discussion

Method validation with NIST 1898 TiO₂ RM yielded a measured mean particle diameter of 79 nm (certificate: 71 ± 4 nm by laser diffraction, 77 ± 7 nm by sedimentation).

In sunscreen samples:

• Sample A contained 0.016 wt % Al(OH)₃ and 0.713 wt % TiO₂ NPs.
• Sample B showed trace Al(OH)₃ (
• Sample C included 0.588 wt % Al(OH)₃, 4.96 wt % TiO₂, and 10.8 wt % ZnO NPs.

NP size distributions in Sample C revealed TiO₂ and ZnO populations below 100 nm. Comparison with total metal concentrations (microwave digest) showed NP/total ratios of 82 % (Al), 90 % (Ti), and 74 % (Zn).

In swimming pool waters:

• Indoor pool showed no detectable NPs.
• Outdoor pools contained TiO₂ between 49 ng/L and 1100 ng/L, and ZnO up to 1610 ng/L.
• The highest NP levels appeared in a small children’s outdoor pool, reflecting sunscreen wash-off.

Rapid multi-element acquisition reduced analysis time and sample vial visits, minimized contamination risk, and enabled element association studies within individual particles.

Benefits and Practical Applications

The Rapid Multi-Element spICP-MS approach:

• Simultaneously characterizes multiple elements in NPs from a single injection.
• Saves time by eliminating repeated uptake/rinse cycles.
• Improves precision and reduces carryover.
• Supports QA/QC in environmental, food, cosmetic, and material research.

Future Trends and Potential Applications

Expanding multi-element spICP-MS to 16 elements will broaden its utility in:

• Tracking multi-metal core-shell NPs in biological and environmental systems.
• Mapping element correlations in natural nanoparticle mixtures.
• High-throughput screening of complex consumer products.
• Regulatory compliance and environmental risk assessments.

Conclusion

The Agilent Rapid Multi-Element Nanoparticle Analysis mode on the 7900 ICP-MS provides an efficient, accurate, and contamination-resistant platform for simultaneous multi-element NP characterization. It offers significant gains in throughput and data quality for diverse analytical applications.

References

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