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News article20 October 20172 min read

Validation of particle tracking analysis for size measurements of particles

PTA measurements in the JRC's Engineering Materials Laboratory
© EU, 2017

Scientists from the JRC and the Veterinary and Agrochemical Research Centre (CODA-CERVA, Belgium) have investigated the performance of a commercial particle tracking analysis device for size analysis of silica and polystyrene nano- and microparticles. The results of this study will help scientists in estimating the uncertainties of their measurement results in this field.

Particle tracking analysis (PTA) is a technique to measure the size of particles with external dimensions in the nano- and sub-micrometre scale range. Recently, a new and improved type of PTA instrument has been developed and commercialised. Following the adoption of the European Commission's Recommendation on a definition of a nanomaterial (2011/696/EU), which refers to number-based size distributions, PTA has attracted great interest because it directly measures such number-based particle size distributions.

In particular for regulatory purposes, measurement procedures must be fully validated to ensure the reliability and comparability of results. Despite its growing popularity, only limited attempts have so far been made to investigate and quantify the performance of the PTA method for particle size analysis.

To assess the PTA's measurement capability, JRC scientists, in collaboration with the Belgian Veterinary and Agrochemical Research Centre (CODA-CERVA), Belgium, conducted a validation study during which monomodal and bimodal suspensions of silica and polystyrene nano- and microparticles were analysed. The study found that monomodal populations of particles, dispersed in purified water, can be measured with an accuracy of 10 %, provided that they are larger than 40 nm in diameter. Silica and polystyrene particles smaller than 40 nm could not be reliably measured due to the method's limit of detection.

The study also showed that bimodal populations can be resolved and quantified provided the ratio of small to big particles is at least 1.25 – that is, sample mixtures in which the size of the smallest particles is about 25 % smaller than the size of the biggest particles. These findings confirm that the PTA method has a superior resolution compared to other ensemble light scattering based techniques such as dynamic light scattering (DLS).

While the study demonstrates the reliability of the particle size aspect of the technique, the reliability of particle number concentrations, obtained with this technique, has yet not been demonstrated yet due to the absence of fit-for-purpose certified reference materials. This second dimension of the measurement challenge must be adequately tackled before the PTA technique can be used to solve regulatory and compliance requirements related to the EC nanomaterial definition.

Read more in: V. Kestens et al., "Validation of a particle tracking analysis method for the size determination of nano- and microparticles", Journal of Nanoparticle Research 19 (2017) 271, doi: 10.1007/s11051-017-3966-8

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Validation of a particle tracking analysis method for the size determination of nano- and microparticles


Publication date
20 October 2017