Quantitative characterization of silica nanoparticles by asymmetric flow field flow fractionation coupled with online multiangle light scattering and ICP-MS/MS detection

Synthetic amorphous silica is one of the two commodity materials dominating the market of nanomaterials in terms of production volume, used in several industrial applications and found in a wide variety of consumers' products including medicines, toothpastes, cosmetics and food. Recent evidence emerged that despite a long history of use further investigation is needed to exclude long-term effects on human health for specific applications, such as food. It is therefore important to have easy, reliable and sensitive analytical methods for the determination of nano-sized silica available. In this work a method for the simultaneous determination of particle size and mass concentration of synthetic amorphous silica nanoparticles by asymmetric flow field flow fractionation coupled with online multiangle light scattering and ICP-MS/MS detection is described. Accurate dimensional characterization of the particles separated by FFF was achieved by means of both ICP-MS/MS detection with size calibrants and standardless sizing by MALS. Element-specific detection by ICP-MS/MS using all the three silicon isotopes, pre-channel mass-calibration with silica nanoparticles and post-channel mass-calibration with elemental standards were used to provide quantitative data on the silicon present in the size fractions separated online by FFF. The FFF-MALS-ICP-MS/MS method developed enabled dimensional and mass determination of silica particles over the size range of approximately 20-200 nm with satisfactory recoveries of the analyte material. The method was successfully applied to the characterization of two test samples, i.e. the reference material ERM-FD100 and a silica suspension having nominal diameters of 20 and 140 nm, respectively.