A Colloidal Silica Reference Material for Nanoparticle Sizing by Means of Dynamic Light Scattering and Centrifugal Liquid Sedimentation Olivier Couteau*, Jean Charoud-Got*, Hubert Rauscher**, Fabio Franchini**, François Rossi**, Vikram Kestens*, Katrin Franks*, Gert Roebben* (Received: 1 October 2009; in revised form: 12 October 2010; accepted: 10 February 2011) DOI: 10.1002/ppsc.200900094 1 Introduction 1.1 General Introduction on Nanoparticles Nanoparticles are particles with all three external di- mensions in the nanoscale, which is the size range from approximately 1 nm to 100 nm, as defined in ISO/TS 27687:2008 [1]. Naturally occurring nanoparticles are abundantly present in the atmosphere. In industrial and densely populated areas, incidentally produced nanopar- ticles, such as those created in combustion processes, sig- nificantly add to the natural abundance of particles in the atmosphere. Exposure to the respirable, fine and ultrafine fraction of particles in our environment has been linked to evidence of adverse health effects. In the related exposure and epidemiological studies, the term ‘ultrafine particles’ is used for particles with an equiva- lent diameter of less than 100 nm (ISO 14644-6:2006, [2]). The difference between the definitions of nanopar- ticles and ultrafine particles is subtle. A third group of nanoparticles, in addition to those occurring naturally or incidentally, are the engineered or manufactured nanoparticles (ENPs). These are pro- duced intentionally, often with the aim of exploiting a difference in behaviour or properties of nanoscaled par- ticles in comparison to bulk material of the same com- Part. Part. Syst. Charact. 00 (0000) 1–13 1 * Dr. O. Couteau, J. Charoud-Got, Ing. V. Kestens, Dr. G. Roeb- ben (corresponding author), Dr. K. Franks, European Commis- sion, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, 2440 Geel (Belgium). E-mail: gert.roebben@ec.europa.eu ** Dr. H. Rauscher, Dr. F. Franchini, Dr. F. Rossi, European Commission, Joint Research Centre, Institute for Health and Consumer Protection (IHCP), Via E. Fermi 2749, 21027 Is- pra, VA (Italy). Abstract IRMM-304 is a new nanoparticle reference material (RM) consisting of silica nanoparticles suspended in an aqueous solution, of which the particle size was charac- terized by dynamic light scattering (DLS) and centri- fugal liquid sedimentation (CLS). The homogeneity and stability of IRMM-304 were confirmed and three method-specific mean particle sizes around a nominal particle size of 40 nm were assigned to the material. The characterization tests have revealed a systematic devia- tion between the measurement results obtained with DLS and CLS. The availability of IRMM-304 makes it possible to study this difference between methods. Sev- eral possible causes for differences between the DLS and CLS results are suggested and preliminarily investi- gated, such as the interaction between particle and sus- pending medium, the particle shape and the effect of polydispersity on the size averaging procedure. These investigations are one illustration of the potential role of IRMM-304 and other nanoparticle RMs in the develop- ment, comparison, improved understanding, and quality assurance of nanoparticle sizing methods. Keywords: centrifugal liquid sedimentation (CLS), dynamic light scattering (DLS), nanoparticles, particle size, reference material (RM) © 2011 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim http://www.ppsc-journal.com