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

Abstract

The volume-specific surface area (VSSA) of a particulate material is one of two apparently very different metrics recommended by the European Commission for a definition of “nanomaterial” for regulatory purposes: specifically, the VSSA metric may classify nanomaterials and non-nanomaterials differently than the median size in number metrics, depending on the chemical composition, size, polydispersity, shape, porosity, and aggregation of the particles in the powder. Here we evaluate the extent of agreement between classification by electron microscopy (EM) and classification by VSSA on a large set of diverse particulate substances that represent all the anticipated challenges except mixtures of different substances. EM and VSSA are determined in multiple labs to assess also the level of reproducibility. Based on the results obtained on highly characterized benchmark materials from the NanoDefine EU FP7 project, we derive a tiered screening strategy for the purpose of implementing the definition of nanomaterials. We finally apply the screening strategy to further industrial materials, which were classified correctly and left only borderline cases for EM. On platelet-shaped nanomaterials, VSSA is essential to prevent false-negative classification by EM. On porous materials, approaches involving extended adsorption isotherms prevent false positive classification by VSSA. We find no false negatives by VSSA, neither in Tier 1 nor in Tier 2, despite real-world industrial polydispersity and diverse composition, shape, and coatings. The VSSA screening strategy is recommended for inclusion in a technical guidance for the implementation of the definition. Graphical abstractWe evaluate the extent of agreement between classification by electron microscopy (EM) and classification by Volume-Specific Surface Area (VSSA) on a large set of diverse particulate substances. These represent the challenges anticipated for identification of nanomaterials by the European Commission recommendation for a definition of nanomaterials for regulatory purposes. Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-017-3741-x) contains supplementary material, which is available to authorized users.

Nanoparticle Characterization: What to Measure?

“…For nonporous materials, the volume‐specific surface area (VSSA) can be used to classify it as a nanomaterial . VSSA is defined according to Equation where S is the external surface of the sample, V is the solid volume, SSA is the specific surface area (surface per mass), and ρ is the material density.…”

Nano or Not Nano? A Structured Approach for Identifying Nanomaterials According to the European Commission’s Definition

“…Being able to experimentally demonstrate that a material is not a nanomaterial is certainly important in view of nanorelated regulatory requirements, especially if those measurements can be performed in a time and costefficient manner. [6,17,18] The NanoDefiner Framework consists of a com prehensive methodology and measurement strategy that sup ports practitioners in industry, regulatory bodies and enforce ment laboratories in implementing the EC NM Definition. [16,19] The NanoDefine Methods Manual [16] describes the NanoDefiner Framework and its tools.…”

“…On the other hand, the possibility to classify a material as a nanoma terial or nonnanomaterial by determining the VSSA, together with the conditions of applicability to use VSSA as classifica tion criteria, is discussed in detail in refs. [18,30]. An overview of determining VSSA with BET is given in ref.…”

“…A fine powder of calcium carbonate CaCO 3 (IRMM384) was tested. According to the MCS, [24] using information on the type of the material (inorganic, dry powder) and the shape of the particles (rod/cigarlike [18] ), the following methods are recom mended for reliable analysis: 1) Tier 1: BET (if the shape is homogenous and the particle size distribution of the sample is monomodal). 2) Tier 2: TEM, SEM, and atomic force microscopy (AFM).…”

A technique-driven materials categorisation scheme to support regulatory identification of nanomaterials

“…None of the available techniques is suitable for all materials. [11][12][13][14][15][16][17][18] However, if such size measurements are to be done to full regulatory obligations, the results must be relevant, reliable and transparent so that the involved parties, i.e. commercial rms and regulators, including non-specialists in the metrology eld, mutually can accept the conclusions drawn from them.…”