Towards a safe and efficient digestion of TiO₂ (nano)particles in confectioneries using HBF₄

Due to potential health concerns, the European Food Safety Authority (EFSA) issued a ban on the use of titanium dioxide (TiO₂) as a food additive in 2021 (Younes et al. 2021). TiO₂ has been widely used as a food additive (referred to as E171), particularly as a brightener or colorant in confectionery (Weir et al. 2012). Predominantly composed of the anatase form, with rutile as the second most abundant, a significant proportion of E171 is nanoparticulate (Bischoff et al. 2020). The regulatory decision (ban on E171) underscores the necessity for reliable analytical methods to assess the presence and quantity of TiO₂ in food, both to support regulatory compliance and to facilitate further toxicological evaluations. The determination of the total Ti content is used as an initial screening method to assess whether samples might contain TiO₂ and subsequently to determine the recovery of size-resolved analyses (e.g., sp-ICP-MS) employing mild extraction to determine size distribution as well as number and/or mass concentrations of TiO₂ NPs. The digestion process is a critical component of the analytical workflow for TiO₂ analysis as an incomplete digestion of the sample can result in significant variability and underestimation of results. Conventional digestion methods using HNO₃ alone are often inadequate due to the high chemical stability of TiO₂, which is why hydrofluoric acid (HF) (Weir et al. 2012) or sulfuric acid (H₂SO₄) (Mudunkotuwa et al. 2016) are frequently employed to ensure complete dissolution. Developing safe yet efficient digestion protocols is therefore a priority for laboratories targeting such challenging analytes.
This Application Report presents the development and optimization of a digestion protocol that employs in situ HF generation using tetrafluoroboric acid (HBF₄). The proposed method offers a safer and more practical alternative to direct HF handling while ensuring similar digestion capacity for TiO₂ NPs.