Comparability of particle size measurement in different laboratories
An interlaboratory comparison study coordinated by the JRC confirms that the term 'particle size' is not sufficient to specify the exact quantity measured by different particle size analysis methods.
Already in 2014, the JRC released a certified reference material (ERM-FD102) for the quality control of nanoparticle size analysis methods. This CRM consists of a mixture of two aqueous suspensions of silica nanoparticles with distinct particle sizes. In order to elaborate the main metrological challenges encountered during the characterisation of this CRM, scientists from the JRC and other Measurement Institutions from Australia, Belgium, China, Germany, and the United Kingdom studied in-depth the average particle diameters of the main particle populations (one around 20 nm and one around 80 nm in diameter) that were obtained through an inter-laboratory comparison study (ILC).
Thirty laboratories participated in the ILC, with a variety of techniques for particle size analysis. The findings of the ILC confirmed that the particle size results of several measurement methods could significantly differ from each other. This is because 'particle size' is usually the size of an equivalent spherical particle that has, in the specific analysis method, the same behaviour as the actual particles, which are not perfectly spherical.
The results of the in-depth study of the results revealed that it is essential to specify the 'kind of particle size' carefully by describing the entire measurement procedure (i.e. from sample preparation to data analysis). An incomplete specification allows for misinterpretation and ambiguity of the meaning or fitness-for-purpose of the reported data.