Reliable nanomaterial classification of powders using the volume-specific surface area method

Area of Science:

• Materials Science
• Nanotechnology
• Regulatory Science

Background:

• The European Commission uses metrics like volume-specific surface area (VSSA) and median particle size for nanomaterial definition.
• Discrepancies in classification can arise due to particle characteristics such as composition, size, shape, porosity, and aggregation.
• Electron microscopy (EM) and VSSA are key methods for nanomaterial identification, but their agreement needs evaluation.

Purpose of the Study:

• To evaluate the agreement between nanomaterial classification by EM and VSSA across diverse particulate substances.
• To assess the reproducibility of EM and VSSA measurements in multiple laboratories.
• To develop and validate a tiered screening strategy for implementing the EU nanomaterial definition.

Main Methods:

• Classification of diverse particulate substances using both electron microscopy (EM) and volume-specific surface area (VSSA).
• Multi-laboratory determination of EM and VSSA to assess reproducibility.
• Development of a tiered screening strategy based on benchmark materials and application to industrial samples.

Main Results:

• VSSA classification showed no false negatives, even with industrial polydispersity and diverse material properties.
• VSSA is crucial for preventing false-negative classification of platelet-shaped nanomaterials by EM.
• Extended adsorption isotherms prevent false-positive classification by VSSA for porous materials.

Conclusions:

• The VSSA screening strategy demonstrates high reliability and is recommended for regulatory guidance on nanomaterial definition.
• VSSA serves as an essential complementary method to EM, particularly for challenging particle morphologies and compositions.
• The proposed tiered screening strategy effectively classifies nanomaterials, minimizing borderline cases for EM.