Determination of trace elements in titanium oxides by wavelength dispersive x-ray fluorescence spectrometry (WD-XRF)

Abstract

TiO₂ is used in a great variety of industries (foods, medicines, cosmetics, etc.). In food industry, although the use of TiO₂ as additive was banned by EU in 2022, it is still authorized in medicinal products, and is allowed as food ingredient in US and Canada. Focusing on cosmetics, regulations state some forbidden elements (As, Cd, Ni, Hg, Sb, and Pb), and others allowed with a specific limit (Co, Cr, and Se). Most researches about TiO₂ characterization are focused on the purity determination and no studies analyzing trace metals in this material have been found. Due to the potential impact of those trace elements on health and safety, a robust method for determining them in TiO₂ is required. A methodology for the determination of As, Cd, Co, Cr, Hg, Ni, Pb, Sb, and Se at trace level in TiO₂ by WD-XRF has been developed. Sample was prepared as pressed pellets to achieve low limits required by regulations, and the best conditions were established using n-butyl methacrylate as binder and plastic spatula to avoid Cr contamination coming from the stainless-steel one. An in-depth inquiry conducted to get calibration and validation standards revealed a lack of reference materials; therefore, additions of pure oxides of each element were made to high-purity TiO₂. Validation was performed by two means: analyzing synthetic standards prepared as stated and analyzing two commercial TiO₂ by an independent method (ICP-OES). The developed methodology was suitable to be used as control method to assess whether the materials meet the regulations, since time required to undertake the analysis is much less than other methods.