Size characterization and quantification of titanium dioxide nano- and microparticles-based products by Asymmetrical Flow Field-Flow Fractionation coupled to Dynamic Light Scattering and Inductively Coupled Plasma Mass Spectrometry

Abstract

A procedure for the size characterization and quantification of titanium dioxide (TiO₂) nano- and microparticles by Asymmetric Flow Field-Flow Fractionation (AF4) coupled to Dynamic Light Scattering (DLS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is described. Different strategies for size characterization with size standards and the use of the DLS signal for the estimation of hydrodynamic diameters are evaluated. The procedure has been applied to the characterization of TiO₂ nanoparticles in photocatalytic products and crab sticks (surimis), where TiO₂ is present as E171 food additive. Sizes in the range of 50-90 nm and 160-170 nm were estimated in the different photocatalytic products by AF4-DLS, in good agreement with the sizes predicted by calibration versus SiO₂ and polystyrene standards. In surimis, sizes between 140 and 350 nm were estimated by AF4-DLS, similar to those reported in literature for E171 additive. These results were also compared to those obtained by single particle ICP-MS, which allowed the detection of a nano-sized fraction of TiO₂ present in the four surimis analyzed. Titanium contents in one of the photocatalytic products determined by AF4-ICP-MS was 16.86 ± 2.54 mg g^-1, whereas the alkaline extraction followed by AF4-ICP-MS allowed the determination of TiO₂ content in four surimis at concentration levels in the range of the μg g^-1 (from 3.14 ± 0.10 to 14.55 ± 1.46 μg Ti g^-1), with channel recoveries above 85% in all cases. The method has been validated by comparison with the Ti content determined by ICP-OES after microwaved assisted acid digestion of all the samples. The methodology proposed allows the complete quantification of the (nano)particulate forms of titanium in complex matrices together with their size characterization.

Keywords: Alkaline extraction; Asymmetric flow field-flow fractionation; Crab sticks (surimi); Photocatalytic products; Single particle inductively coupled plasma-mass spectrometry; Titanium dioxide nanoparticles.