Date Published: June 20, 2017
Publisher: Springer Berlin Heidelberg
Author(s): Stefan Weigel, Ruud Peters, Katrin Loeschner, Ringo Grombe, Thomas P. J. Linsinger.
Single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS) promises fast and selective determination of nanoparticle size and number concentrations. While several studies on practical applications have been published, data on formal, especially interlaboratory validation of sp-ICP-MS, is sparse. An international interlaboratory study was organized to determine repeatability and reproducibility of the determination of the median particle size and particle number concentration of Ag nanoparticles (AgNPs) in chicken meat. Ten laboratories from the European Union, the USA, and Canada determined particle size and particle number concentration of two chicken meat homogenates spiked with polyvinylpyrrolidone (PVP)-stabilized AgNPs. For the determination of the median particle diameter, repeatability standard deviations of 2 and 5% were determined, and reproducibility standard deviations were 15 and 25%, respectively. The equivalent median diameter itself was approximately 60% larger than the diameter of the particles in the spiking solution. Determination of the particle number concentration was significantly less precise, with repeatability standard deviations of 7 and 18% and reproducibility standard deviations of 70 and 90%.
Particles with dimensions in the nanoscale (defined as 1–100 nm by ISO/TS 80004-1 ) may show different properties from the same chemical material in its bulk form, either due to the increased surface-to-volume ratio or the emergence of quantum phenomena at these small ranges. Such particles not only have a significant potential for improved material properties but may also have adverse effects. Legislation requiring the labeling of the presence of materials in their nanoform in cosmetics  and food  exists at the EU level. To avoid a multitude of conflicting definitions of nanomaterial, the European Commission has published a recommendation for a definition  which it intends to use in future regulation. This definition defines a nanomaterial as “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 nm-100 nm.”
Nine of the ten participants submitted valid results. One laboratory could not detect particles: the modal particle diameter decreased with dilution from 55 nm at a dilution of 1:3000 to 30 nm at a dilution of 1:10,000. The laboratory, therefore, suspected that the silver nanoparticles were destroyed by the preparation procedure to give an ion-like behavior in the analyzed dispersion.
The interlaboratory study showed promise for the determination of the median particle diameter: reproducibility standard deviations between 15 and 25% are not unusual and are deemed acceptable for the determination of many contaminants in food. Bearing in mind that the AgNP mass fraction in the samples in this study was rather high (0.1 and 0.5 g kg−1), further studies are needed to evaluate whether this level of agreement can also be obtained at the lower AgNP mass fractions, more likely to be caused by contamination from food contact materials.