High sensitivity analysis of SiO2 nanoparticles using the Agilent 8900 ICP-QQQ in MS/MS mode

Significance of the Topic

Nanoparticles such as silicon dioxide (SiO2) are increasingly integrated into industrial processes, consumer products, and pharmaceuticals, raising concerns over their environmental fate and potential health impacts. Accurate characterization of these particles in complex matrices is essential for risk assessment, quality control, and regulatory compliance.

Objectives and Study Overview

This work evaluates the performance of the Agilent 8900 triple quadrupole ICP-MS (ICP-QQQ) operating in MS/MS mode with hydrogen cell gas for single particle ICP-MS (spICP-MS) analysis of SiO2 nanoparticles. The study aims to determine particle size distributions, concentrations, and the effectiveness of interference removal under various sample conditions.

Methodology and Instrumentation

Fast Time Resolved Analysis (fast TRA) was employed with a 0.1 ms dwell time and no settling between measurements. Reference SiO2 nanoparticles (50, 60, 100, 200 nm) were diluted to 40–1000 ng/L in deionized water, sonicated for homogenization, and introduced via a concentric glass nebulizer into a quartz spray chamber.

Hydrogen Cell Gas:

• H2 at 2.0 mL/min for aqueous samples and 3.0 mL/min for 1 % ethanol matrix to remove 12C16O and 14N2 interferences at m/z 28.

Nebulization Efficiency:

• Determined by comparing sample uptake and spray chamber drain mass flows.
• Cross-checked against gold nanoparticle reference material.
• Measured efficiency: 6.5 % under the chosen operating conditions.

Instrument Configuration:

• Agilent 8900 ICP-QQQ (#100) with Q1 and Q2 both set to m/z 28.
• Nickel sampling and skimmer cones; quartz torch with 1 mm injector; peristaltic pump at 0.35 mL/min; carrier gas at 0.76 L/min; RF power at 1550 W.
• Single Nanoparticle Application Module in MassHunter for automated calibration and data processing.

Main Results and Discussion

• Distinct signal peaks for individual SiO2 nanoparticles down to 50 nm, with a background equivalent diameter of 22 nm.
• Measured median, mode, and mean diameters closely matched TEM values (e.g., 49–50 nm measured vs. 46.3 ± 3.1 nm TEM for the 50 nm sample).
• Particle concentrations determined by spICP-QQQ agreed with prepared concentrations (e.g., 92 ng/L measured vs. 100 ng/L prepared for 100 nm).
• The log–log plot of mean signal intensity versus TEM diameter yielded a slope of 2.84, confirming the theoretical cubic relationship between mass and diameter.
• In a 1 % ethanol matrix, H2 cell gas effectively suppressed carbon-based interferences, enabling clear separation of mixed 100 nm and 200 nm populations.

Benefits and Practical Applications

The MS/MS approach with hydrogen cell gas offers robust polyatomic interference removal and low background, while high sensitivity and dedicated software enable rapid, accurate size and concentration measurements. This method supports environmental monitoring, food safety analysis, materials QA/QC, and nanotoxicology studies.

Future Trends and Potential Applications

• Expansion to multi-element nanoparticle characterization and real-time monitoring.
• Integration with separation techniques (e.g., field-flow fractionation) for complex matrices.
• Development of novel reaction/collision gases to address broader interferences.
• Advanced software algorithms for automated data interpretation and reporting.
• Increased availability of certified nanoparticle reference materials and standardized protocols.

Conclusion

The Agilent 8900 ICP-QQQ in MS/MS mode with hydrogen cell gas, combined with spICP-MS software, provides precise and sensitive SiO2 nanoparticle analysis. This approach overcomes common silicon interferences, delivers accurate sizing and quantification down to under 50 nm, and offers high throughput for diverse research and industrial applications.

References

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