Researchers at the European Commission Joint Research Centre in Belgium developed a methodology to characterise materials containing nanoparticles, using asymmetric flow field-flow fractionation (AF4) in combination with various measurement techniques including dynamic light and multi-angle light scattering.
“The purpose of the study was to propose an approach based on the use of experimental design for the optimisation of the AF4 method to characterise polydisperse-coated TiO2. The availability of this method is considered as an important prerequisite to investigate the nano-characteristics of TiO2 containing food and feed additives,” the EC study’s authors wrote.
The difficulty of measuring nanomaterials
In 2011 the EC defined a nanomaterial as: “a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1–100 nm.”
But while the definition is clear, the actual characterisation of nanomaterials has proved to be a challenge, with multiple techniques being required to investigate the size of particles in a given material, according to the study’s authors.
By using AF4 in combination with a variety of measurement systems, the researchers aimed to produce a single methodology for defining nanomaterials.
In the case of the TiO2 material under investigation, the researchers showed a size distribution of particles with diameters between 50.5-197.9nm, which corresponded with previous research on the same material.
“This approach allowed the identification of optimal experimental conditions, while the required number of experiments was minimised. Finally, the optimised method protocol was applied to replicate analyses of polydisperse TiO2, showing acceptable values for repeatability (< 3%) and recovery (> 60%),” wrote the authors in their study.
Challenges remain, but real results to follow
According to Joseph Waldstein, press officer for the EC, here are still several technical challenges before the technique can be used to implement the nanomaterial definition. These include measuring particles within aggregate materials, and how to interpret experimental signals into accurate size distributions.
“In the particular case of the field flow fractionation technique, one of the limitations is that it requires the development of dedicated material-specific test protocols in order to obtain reliable particle size distributions, therefore a range of analytical methods would be required to investigated whether nanomaterials fulfil the regulatory definitions,” said Waldstein.
Despite these remaining challenges, the methodology is already being used to characterise real-world nanomaterials, according to the study’s authors.
“The same approach employed in this study was successfully applied to the characterisation of several non-coated and commercially available polydisperse TiO2 materials, some authorised and used as feed additives in the European market,” they wrote.
“These results, together with the assessment of a number-based size distribution of these materials which is being carried out at the moment, will be presented in a second study.”
Source: Food Additives & Contaminants
Published online ahead of print, doi: 10.1080/19440049.2016.1239031
“Optimisation of asymmetric flow field-flow fractionation for the characterisation of nanoparticles in coated polydisperse TiO2 with applications in food and feed”
Authors: J. Omar, A. Boix, G. Kerckhove, and C. von Holst