Determination of size distribution of colloidal TiO2 nanoparticles using sedimentation field-flow fractionation combined with single particle mode of inductively coupled plasma-mass spectrometry

Sedimentation field-flow fractionation (SdFFF) provides mass-based separation of colloidal particles, and thus a size-based separation if the particles are of uniform density. The particle size can be measured from the retention time in SdFFF if the density of the particle is known. In the single-particle mode of inductively coupled plasma-mass spectrometer (SP-ICPMS), the signal intensity depends on the particle size, and the signal frequency is proportional to the particle concentration. In this study, SdFFF was employed for size-based separation and size analysis of two types of TiO2 nanoparticles, rutile and anatase, having rather broad size distributions. SdFFF provided high enough resolution to show the difference in size distributions between two samples, for which dynamic light scattering (DLS) could not show clearly. SdFFF fractions were collected and analyzed by SP-ICPMS to determine size distributions of the SdFFF fractions. The sizes and Ti concentrations of SdFFF fractions of TiO2 colloids determined by SP-ICPMS were well correlated with SdFFF results. Results revealed that SP-ICP could become a useful tool for size-based separation and also for size analysis of various types of colloidal nanoparticles, when it is combined with a particle separator such as SdFFF, especially for samples having relatively broad size distributions.