Paul Kippax alerted me to an interesting piece in Chemical Watch (Global Risk and Regulation News). It’s based on a comment by the European Commission Joint Research Council (JRC) that:

The term “particle size” does not sufficiently describe the exact quantity that is measured, across different nanomaterial particle size analysis (PSA) methods’.

Our findings show that the equivalent diameter values of some measurement methods do not agree and that the results of some others only agree, due to their relatively large uncertainties,” the study authors say.

For a reliable comparison of particle size, we propose a more detailed specification of the measure and particle size, including the physical principle of the measurement method and the data analysis procedures.

They add: “An incomplete specification leaves room for misinterpretation, along with ambiguity about the meaning or the fitness-for-purpose of the reported data’.


Now, I’m sure we’d all agree that detailed reporting of experiments and ancillary information is vital in all sciences.  Indeed, ISO particle size standards from the TC24/SC4 Particle Characterization Technical Committee carry a mandatory reporting section – everything from the name of the operator to more details in terms of applied constants and parameters (for example the imaginary component of the refractive index for laser diffraction). But that’s not my main point.  Readers of this blog may have seen or even have a copy of the ‘Basic Principles of Particle Size Analysis’ (dating from 1993) where we talk about equivalent spheres and concepts supported by a webinar or two:

March 30th, 2011 The Basic Principles of Particle Size Analysis” Part 1 – Overview and the numbers

So here we see a nice diagram showing some of the different answers possible for a single grain of sand for instance:

Particle size standard

of an irregular particle surrounded by 7 different but equally correct equivalent spheres with their appropriate diameters. Isn’t that what JRC was saying?

Déjà vu and nostalgia ain’t what they used to be. Happy reading!

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