Certification of the equivalent spherical diameters of silica nanoparticles in aqueous solution : certified reference material ERM-FD304

This report describes the certification of several equivalent spherical diameters of silica nanoparticles in aqueous solution, Certified Reference Material (CRM) ERM®-FD304. The CRM has been certified by the European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, BE. ERM-FD304 consists of silica nanoparticles suspended in aqueous solution. The intended use of this CRM is to check the performance of instruments and methods that determine the diameter of nanoparticles suspended in liquid medium. The CRM is available in 10 mL pre-scored amber glass ampoules containing approximately 9 mL of suspension. The CRM was prepared from commercially available colloidal silica, Ludox®, grade TM-50 (Grace Davison GmbH, Worms, Germany) Production of the CRM included testing of the homogeneity and stability of the ampouled diltuted raw material, as well as the characterisation using an interlaboratory comparison approach. The CRM has been certified for the scattering intensity based harmonic mean diameter using Dynamic Light Scattering (DLS) and for the extinction intensity based modal Stokes diameter of the silica nanoparticles in aqueous solution using Centrifugal Liquid Sedimentation (CLS) - line start method. An indicative value for size measurements using electron microscopy and information values for pH and ζ-potential were assigned as well. Expanded uncertainties are estimated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) with a coverage factor of k=2, corresponding to a level of confidence of about 95%.