Characterisation of titanium dioxide (nano)particles in foodstuffs and E171 additives by single particle inductively coupled plasma-tandem mass spectrometry using a highly efficient sample introduction system.

Abstract

This study addressed primarily the characterisation and quantification of titanium dioxide (TiO₂) (nano)particles (NPs) in a large variety of commercial foodstuffs. The samples were purchased from local markets in Spain before the ban of TiO₂ food additive (E171) in the EU. The analyses were carried out by single particle inductively coupled plasma-tandem mass spectrometry (spICP-MS/MS) in mass shift mode (oxidation of ⁴⁸Ti to ⁴⁸Ti¹⁶O (m/z = 64)) and using a highly efficient sample introduction system (APEX™ Ω). This novel analytical approach allowed accurate characterisation of a large panel of TiO₂ NPs sizes ranging from ∼12 to ∼800 nm without isobaric interferences from ⁴⁸Ca isotope, which is highly abundant in most of the analysed foodstuffs. TiO₂ NPs were extracted from foodstuffs using sodium dodecyl sulphate (0.1%, w/v) and diluted with ultra-pure water to reach ∼ 1000 particles signals per acquisition. All the analysed samples contained TiO₂ NPs with concentrations ranging from 10¹⁰ to 10¹⁴ particles kg^-1, but with significant low recoveries compared to the total Ti determination. A selection of samples was also analysed using a similar spICP-MS/MS approach with a conventional sample introduction system. The comparison of results highlighted the improvement of the limit of detection in size (12 nm) by the APEX™ Ω system, providing nanoparticulate fractions ranging from ∼4% (cheddar sauce) up to ∼87% (chewing gum), which is among the highest nanoparticulate fractions reported in literature using a spICP-MS approach. In addition, two commercially available E171 additives were analysed using the previous approaches and other techniques in different European laboratories with the aim of methods inter-comparison. This study provides occurrence data related to TiO₂ NPs in common commercial foodstuffs but it also demonstrates the potential of the novel analytical approach based on APEX™-ICP-MS/MS to characterise nano-size TiO₂ particles in complex matrices such as foodstuffs.