Coupling of asymmetric flow field flow fractionation to ICPMS for nanoparticle analysis

Importance of the Topic

The rapid integration of engineered nanoparticles into consumer products demands robust analytical techniques for size-resolved characterization. Among these, silver, titanium dioxide and zinc oxide nanoparticles are prevalent in sprays, raising concerns about human exposure, transport and potential health risks. Effective monitoring in aerosols and liquids requires sensitive, selective methods capable of discriminating particle size distributions and elemental composition.

Objectives and Overview of the Study

The study targeted the development and validation of a hyphenated technique combining asymmetric flow field flow fractionation (AF4) with inductively coupled plasma mass spectrometry (ICPMS) for nanoparticle analysis. Silver nanoparticles from a consumer spray product were separated by size and quantified, with results compared to electron microscopy imaging to assess accuracy and reliability.

Methodology and Instrumentation

Nanoparticle separation was performed using AF4, exploiting a laminar channel flow and crossflow to fractionate particles according to hydrodynamic size. Calibration employed NIST traceable gold standards at 10, 30 and 60 nm diameters. Separated fractions were directed into an ICPMS detector operating in E-Scan mode with a 300 ms integration time, enabling element-specific quantification.

Used Instrumentation

• Wyatt Eclipse3 AF4 System equipped with a 30 kDa PVDF membrane and a 350 µm channel spacer.
• Thermo Finnigan Element2 ICPMS with 1400 W RF power, cooled quartz spray chamber and ESI PFA-ST nebulizer at 1 L/min.

Main Results and Discussion

• Calibration curves based on gold nanoparticle standards showed a clear retention time–size correlation, enabling accurate size distribution calculations.
• Analysis of a diluted silver spray revealed a polydisperse distribution between approximately 6 and 30 nm.
• Results correlated strongly with transmission electron microscopy, confirming method validity.
• Aerosolization experiments indicated transient agglomeration, with larger particle aggregates forming under spray conditions.

Benefits and Practical Applications

The AF4–ICPMS coupling offers:

• High sensitivity and element-specific detection across a broad size range.
• Quantitative, size-resolved data matching electron microscopy accuracy without extensive sample preparation or high operational costs.
• Flexibility for routine monitoring of nanoparticle content in consumer products, environmental samples and industrial process streams.

Future Trends and Potential Applications

Advancements may include integration with multiangle light scattering and UV/VIS detectors for simultaneous morphological characterization. Automation and inline sampling could facilitate real-time monitoring in manufacturing and environmental assessment. Applying this approach to complex matrices such as biological fluids and soils will enhance risk evaluation and regulatory compliance for nanomaterials.

Conclusion

The AF4–ICPMS technique demonstrated robust, reliable size-based separation and elemental analysis of silver nanoparticles, offering a practical alternative to traditional microscopy methods. Its sensitivity, throughput and comparability to electron imaging underscore its value for research, quality control and safety assessment of nanoparticle-containing products.

References

1. Hagendorfer H., Ulrich A., Roessner D., Schneider M., Jocks T. Coupling of asymmetric flow field flow fractionation to ICPMS for nanoparticle analysis. EMPA - Swiss Federal Laboratories and Wyatt Technology Europe GmbH, 2010.