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.
Highlights
The European Commission (EC) published a recommendation on the definition of nanomaterial (NM) for61 Page 2 of 16 regulatory purposes (European Commission 2011)
We find no false negatives by volume-specific surface area (VSSA), neither in Tier 1 nor in Tier 2, despite real-world industrial polydispersity and diverse composition, shape, and coatings
All available data was averaged and can be found in Table 2; more details are provided in the supporting information, : Derivation of the quantity dminVSSA; Calculation of the uncertainty introduced by the aspect ratio cutoff values; Calculation of multimodal material VSSA; electron microscopy (EM) data for NanoDefine materials, including SEM method on platelets; EM, BET, density data for the Joint Research Centre (JRC)/ Eurocolour materials; EM, BET, density data for the further real-world industrial materials
Summary
The European Commission (EC) published a recommendation on the definition of nanomaterial (NM) for. Many possibilities exist (Roebben et al 2014) when materials which are unambiguously NMs according to the size criterion can exhibit a VSSA below 60 m2/cm3 This can be the case for specific particle shapes, for example, fibers or platelets, having only two or one external dimension between 1 and 100 nm, respectively. A quantitative relation between the VSSA and the particle size as measured by electron microscopy (EM, as a general term for scanning electron microscopy, SEM and transmission electron microscopy, TEM), using the available VSSA corrections for particle shape and porosity, will be demonstrated for the first time on a set of representative industrial materials These materials are part of the European research project NanoDefine (http://www.nanodefine.eu) and a joint study by the JRC and Eurocolour (Pena et al 2014 ). All available data was averaged and can be found in Table 2; more details are provided in the supporting information, : Derivation of the quantity dminVSSA; Calculation of the uncertainty introduced by the aspect ratio cutoff values; Calculation of multimodal material VSSA; EM data for NanoDefine materials, including SEM method on platelets; EM, BET, density data for the JRC/ Eurocolour materials; EM, BET, density data for the further real-world industrial materials
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