Towards routine analysis of TiO2 (nano-)particle size in consumer products: Evaluation of potential techniques

In this work, the potential of several techniques commonly used in research studies for TiO2 nanoparticles' (NPs) characterization was evaluated for the implementation in routine analysis. Namely, Dynamic Light Scattering (DLS), single-particle mode Inductively Coupled Plasma Mass Spectrometry (spICP-MS) and Asymmetrical Flow Field-Flow Fractionation coupled to Multi Angle Light Scattering and (single particle) Inductively-Coupled Plasma Mass Spectrometry (AF4-MALS-(sp)ICP-MS) were assessed for this purpose. Electron Microscopy was also used to confirm the validity of results and to obtain information about the shape of the particles. Each instrument was optimized according to routine analysis criteria using reference materials for instrument performance and quality assurance. Then, the methodology was applied to two types of samples of consumer products (sunscreens and sugar-coated chocolate candies), where particle size and concentration obtained by each technique were discussed. Results indicated that TiO2 particles were found in both samples. AF4-MALS-ICP-MS and spICP-MS were powerful tools to characterize TiO2 NPs in real samples, with spICP-MS being more adapted to routine analysis. DLS and electron microscopy provided comparable results for the particle size. The studied sunscreen complied with the European regulation (No 1223/2009) in relation with NPs because the particle size found for TiO2 was in the range 80-110 nm and the reference to nano required is present in the label of the product. Sugar-coated chocolate candies may contain NPs according to DLS and AF4-MALS-ICP-MS results, but particles larger than 100 nm were found by spICP-MS.