Work Package 2

Verification of the performance of number concentration measurements for relevant RT

The aim of this WP is to evaluate the performance of established reference and laboratory methods for number concentration measurements of complex particles (using the RTMs provided by WP1), as well as to assess capabilities of novel methods, such as FCCS/FCS, establish a traceability chain for ensemble methods and to reduce measurement uncertainty associated with number concentration measurements overall (Obj. 2).

This extends current measurement capabilities described in the "ISO/TS 24672:2023 Nanotechnologies ‑ Guidance on the measurement of nanoparticle number concentration" of both particle‑by‑particle and ensemble methods across the different categories of particles with sizes between 1 and 1000 nm, particle densities between 1 g cm‑3and 20 g cm‑3, RI between 0.05 and 3 and number concentrations between 103 and 1014 g‑1.

Close-up of a microscope lens focusing on a slide with gloved hands nearby.

Tasks under WP2

Task 2.1: Particle counting methods for number concentration measurements

First, the materials will be characterised with particle‑by‑particle methods to establish a consensus reference and comparison point for the available RTMs.

Task 2.2: Comparison of number concentration measurements using ensemble methods

Then, an internal ILC between the participants (and potentially project stakeholders) using ensemble methods will be performed (Task 2.2). At this stage, known tabulated or bulk material density and RI values will be assumed, as these are typically used as input parameters by ensemble methods.

In both Task 2.1 and Task 2.2, sample preparation protocols will be developed or improved where required. Especially for imaging methods, material‑specific protocols will be developed as part of Task 2.1, in close collaboration with the work of ISO/PWI TS 21551 "Nanotechnologies ‑ Methods for sample preparation for particle size measurements by electron microscopy and atomic force microscopy".

Task 2.3: External ILC and establishment of uncertainty budgets for number concentration measurement

Finally, with the protocols developed in Task 2.1 and Task 2.2 a VAMAS ILC including external participants will be performed (Task 2.3). In this ILC, RI and density values measured in WP3 will be provided to the participants together with the sample handling and measurement protocols. This will extend current measurement capabilities of ensemble methods to complex particles, reduce associated measurement uncertainty and improve the traceability chain in number concentration measurements through well‑characterised RI and density input parameters.