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.