Towards improved reliability in the determination of TiO2 (nano)particles by single particle inductively coupled plasma-mass spectrometry : application to food characterisation and migration studies

Titanium dioxide (TiO₂) appears to be one of the most employed pigments in the industry due to its specific structural, optical, electronic and photocatalytic properties. It is a solid, crystalline, white and bright, odourless inorganic substance in the form of a powder with particles size ranging from the nanometre (nm) to the micrometre (µm) scale. TiO₂ has been used for decades as a coloring additive in food (E171), especially in candies, chewing gums and frostings. However, since the first report regarding the presence of TiO₂ having particles with size < 100 nm (NPs), the concern about the toxicity of E171 increased, which led recently (2022) to an European Regulation banning the use of this additive in food in the European Union (EU). Food-grade TiO₂ is, however, still used in food industry outside the EU and in food packaging all around the world, thus the question of the migration of TiO₂ particles in food is raised. Reliable analytical methods for the characterisation of TiO₂ are still necessary to assess human exposure by ingestion of food contaminated with E171 and TiO₂-based food packaging.

The Ph.D. project addressed primarily the development and various applications of a new approach for the characterisation (detection and quantification) of NPs in complex matrices such as foodstuffs and food simulants by inductively coupled plasma-mass spectrometry in combination with the single particle approach (spICP-MS). Among the relatively large panel of available techniques for the characterisation of (nano)materials, spICP-MS shows promising features since it allows the rapid screening and analysis of the individual particles in the sample, either in terms of concentration (down to ng/L levels) and size (from ~ 30 to 900 nm).

The first part of the thesis describes the development and validation of a novel method based on spICP-MS/MS using a high efficiency sample introduction system (APEX™) for the characterisation and quantification of TiO₂ NPs in food simulants. The accuracy was demonstrated for both particle size determination and quantitative measurements, and the method’s uncertainty was also calculated. The APEX™ proved to be an excellent approach to avoid matrix effects and increase the sensitivity of the method allowing the detection of particles as small as 12 nm.

The second part of the thesis consisted in the application of the developed method for two different studies. On the one hand, the APEX™-spICP-MS/MS method was used for the assessment of TiO₂ NPs migration from food packaging into food simulants upon storage, showing very low migration yield of TiO₂ NPs from food packaging in standard contact conditions of storage. On the other hand, the method was applied to the characterisation of TiO₂ NPs from E171 in food samples. The main objective was to assess the feasibility of the method for the analysis of real food matrices, especially regarding the detection and quantification of the nanoparticulate fraction (% of particles having a diameter < 100 nm). In addition, a pilot inter-comparison study on the characterisation of E171 additive was performed using different techniques at different laboratories in France and abroad.

The last part of the thesis consisted of the development of an in-house approach (based on python code) for spICP-MS data treatment to assess the main parameters influencing the method uncertainty related to the characterisation of TiO₂ NPs by spICP-MS.

inductively coupled plasma mass spectrometry, titanium oxide, TiO₂ nanoparticles, single particle ICP-MS/MS, high efficiency sample introduction system, E171 additive, foodstuffs, migration and food packaging

Full document (EN): TEL-04678080