Characterization of Iron Nanoparticles in Hydrocarbon Matrices by Single Particle (sp)ICP-MS

Significance of the topic

Accurate measurement of metal nanoparticles in hydrocarbon matrices is crucial for both petrochemical and semiconductor industries. Iron‐based particles can catalyze corrosion in refinery equipment and create defects in silicon wafers, impacting product quality and safety. Single particle ICP-MS (spICP-MS) offers elemental specificity and quantitative particle sizing in complex organic media, filling a gap left by traditional aqueous‐based nanoparticle analysis methods.

Study Objectives and Overview

This study evaluates an Agilent 7900 ICP-MS method, enhanced by solvent‐compatible nanoparticle reference materials (RMs), for characterizing gold and iron oxide nanoparticles dispersed in nonpolar solvents. Key goals included validating the spICP-MS approach against TEM, determining method performance for newly developed organic‐stable RMs, and applying the technique to real petroleum SRMs.

Methodology and Instrumentation

The method combines fast time‐resolved acquisition (100 μs dwell time) on the Agilent 7900 ICP-MS with dedicated spICP-MS software for automated response factor, threshold, and nebulization efficiency calculations. Instrumentation details:

• Agilent 7900 ICP-MS with glass concentric nebulizer, quartz spray chamber, 1.0 mm ID injector, ORS4 collision cell (He mode) and optional H₂ cell gas
• Oxygen addition to carrier gas to prevent carbon deposition
• Peristaltic pump with solvent‐resistant tubing for direct injection of o‐xylene dilutions

Elemental response factors were measured using Au and Fe soluble standards in hydrocarbon oil. Nebulization efficiency (ca. 5 %) was determined with a 100 nm Au nanoparticle RM.

Key Results and Discussion

Ultrastable polystyrene-coated Au nanoparticles (40 nm, 100 nm) and octadecylsilane‐modified silica-shelled Fe₃O₄ nanoparticles (60–70 nm) were synthesized for organic solvent compatibility. spICP-MS size measurements agreed within ±10 % of TEM values for both Au and Fe RMs. In testing NIST SRMs (crude oil 8505 and residual fuel oil 2717a), natural Fe nanoparticle populations were quantified with mean sizes of 77 nm and 68 nm, consistent with TEM ranges. Trajectory scans showed strong separation of particle signals from background, enabling reliable particle counting and sizing.

Benefits and Practical Applications

• Provides quantitative, element‐specific nanoparticle characterization in nonpolar matrices
• Simplifies method setup and data processing through dedicated software module
• Supports method validation and proficiency testing for petroleum and semiconductor quality control
• Complements imaging techniques by delivering statistically robust size distribution and particle number data

Future Trends and Opportunities

Advancements in spICP-MS cell technologies (e.g., mixed reaction gases) may further enhance detection limits for trace metals in organic media. Development of additional solvent‐stable RMs across a broader size and composition range will expand application to additives, catalysts, and environmental samples. Integration with hyphenated separation techniques could enable speciation analysis of nanoparticle surface chemistries.

Conclusion

The Agilent 7900 ICP-MS in spICP-MS mode, paired with novel solvent‐compatible nanoparticle reference materials, delivers accurate and reproducible sizing and counting of metal nanoparticles in complex hydrocarbon matrices. This approach offers a robust analytical platform for industry quality assurance and research applications where knowledge of nanoparticle content is critical.

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