Bilateral evaluation of certified reference materials for macro and trace elements in food as control materials for spICP-MS

The suitability of existing certified reference materials (CRMs) intended for analysis of macro and trace elements in food as effective control materials for single particle inductively coupled plasma-mass spectrometry (spICP-MS) was examined. The presence of nanoparticles (NPs) in these CRMs was evaluated in parallel at two independent laboratories with a focus on matrices such as wheat flour, mussels, and multielement/multivitamin tablets. In general, this bilateral comparison resulted in a good agreement for the determination of different metal-containing NP diameters and particle size distributions (PSDs) for NIST SRM 1567a (wheat flour), NIST SRM 2976 (mussel tissue), NIST SRM 3294 (multielement tablets), and NRC VITA-1 (low-level multivitamin tablets). We provide evidence regarding the impact of the processing software on the computation of the size limit of detection and, hence, on resulting PSDs. However, despite similar sample preparation, instrumental settings, and data processing approaches, the bilateral comparison revealed interlaboratory differences in particle number concentration (PNC), indicating that achieving reproducible PNC results by spICP-MS in complex samples remains analytically challenging. Lastly, a selection of marine animal- and plant-based CRMs was screened for the presence of metal-containing NPs to identify potential candidates suitable for further in-depth quantitative efforts, revealing the presence of large numbers of Al-, Fe-, and Si-containing NPs.