Comparison of the effects of different protocols on the particle size distribution of TiO₂ dispersions

There is a need to standardize methods associated with the dispersion of nanomaterials in nano(eco)toxicological investigations. The first step toward this goal is to understand the degree of variability that exists in nanomaterial dispersions prepared by using different protocols. Using two case studies, the degree of variability in TiO₂ nanomaterial dispersions was assessed by differential centrifugal sedimentation (DCS) methods. Case study 1 addresses the variability that arises from variations within one protocol, investigating the effects of dispersion aging, sonication exposure time, sonication in the presence/absence of an ice bath, material subsampling, particle concentration and having a pre-wetting step. Case study 2 addresses the variability between four different protocols developed through past research activities and projects. The results indicate that there is a large degree of variability (relative standard deviation (RSD) of mean particle diameter = 26%) in the dispersion of TiO₂ nanomaterials between the four different protocols studied and that several steps in a dispersion protocol are potential sources of variation, with final particle concentration being the most significant. The implication of this study is clear: for the purpose of data comparability, there is a need to provide the exact details of all steps involved in a dispersion protocol.