Versailles Project on Advanced Materials and Standards (VAMAS) Interlaboratory Study on Measuring the Number Concentration of colloidal gold nanoparticles
Caterina Minelli, Karen E. Murphy, Monique Johnson, Antonio Montoro Bustos, Jeffrey Fagan, Ingo Strenge
We describe the outcome of an international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 54 laboratories enrolled in this study, including national measurement institutes, academic institutions, research organisations, instrument manufacturers, measurement service providers and industrial laboratories. A total of 76 measurement reports were received from the participants, 25 % of which were for measurements using the particle tracking analysis method (PTA), 22 % using single particle inductively coupled plasma mass spectrometry (spICP-MS), 37 % using ultraviolet-visible (UV-Vis) light spectroscopy, 13 % using centrifugal liquid sedimentation (CLS) and 2.6 % using small angle X-ray scattering (SAXS). The sample distributed in the study consisted of spherical gold nanoparticles of nominally 30 nm in diameter. The study provides quantitative data to evaluate repeatability of these methods and reproducibility of the measurement of number concentration of nanoparticles based on common measurement protocols. The study included different instrument models, users with different levels of experience and tested, to some extent, the impact of experimental procedures for the preparation of the samples on the measurement outcome. We find that the ensemble methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, the latter resulting at 3 %, 7 % and 1.4 % respectively. However, results may be significantly biased for reasons including inaccurate materials properties whose values are used to compute the number concentration. On the contrary, results from particle-by-particle methods appear less biased, but also less reproducible, with measured variability of 72 % and 42 % for PTA and spICP-MS respectively. For PTA we observed, however, that considering the laboratories with a bias below 50%, the resulting average bias was 2.5 % and reproducibility 26 %. For spICP-MS, the overall average number concentration was found to be within 7 % of the reference value. Importantly, the study provides the particle community with some comparative data to underpin measurement reproducibility and method validation, which will improve laboratory practice and provide confidence on current available measurement techniques and results, as well as inform the development of new documentary standards and reference materials. Furthermore, as not all methods are suitable for all materials or particle size range, the results from this study underpin comparability across different types of sample.
, Murphy, K.
, Johnson, M.
, Montoro Bustos, A.
, Fagan, J.
and Strenge, I.
Versailles Project on Advanced Materials and Standards (VAMAS) Interlaboratory Study on Measuring the Number Concentration of colloidal gold nanoparticles, Nanoscale, [online], https://doi.org/10.1039/D1NR07775A, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933164
(Accessed June 7, 2023)