Optimization of mineralization methods of TiO2 nanoparticles: Determination of titanium levels in rat organ tissues

Titanium dioxide nanoparticles (TiO2 NPs) are among the highest produced nanoparticles in the world today and are increasingly being incorporated into a wide range of construction and domestic products. Production on such a massive scale raises questions concerning their human and environmental toxicity. In order to draw appropriate conclusions about the possible adverse biological effects of TiO2 NPs, the so-called “dose-effect” relationship must be explored. This requires proper quantification of titanium in complex matrices such as animal organs. For metal oxide nanoparticles, the use of ICP-MS, a cornerstone in analytical chemistry, is not straightforward.
This study presents the method development for mineralizing TiO2 NPs for analysis of biological tissues. We compare the recovery and quantification limits (LOQ) of the four most commonly used mineralization methods for metal oxides: A. Microwave-assisted dissolution in a HNO3/H2O2 mixture; B. Microwave-assisted digestion in a HNO3/HF/HCl mixture; C. Microwave-assisted dissolution in a HNO3/HF mixture followed by H2O2 treatment; D. Persulfate fusion. Method C produced the best results for a TiO2-NPs suspension, with 96 ± 8 % recovery and a LOQ as low as 0.885 µg/L. It provides rapid and simple determination of ultratrace amounts of titanium NPs in a majority of biological matrixes tested.
Method C was then used for the determination of titanium levels in tissue samples taken from non-exposed rats. Our results are comparable to those found in the literature, but with a slightly lower LOQ. These showed that the Method Quantification Limit was matrix-dependent. For example, the method is not sensitive enough to quantify titanium levels in a single olfactory bulb and in hippocampus in control rats. Bearing this limitation in mind, the method could be applicable to in vivo studies of TiO2-NPs biokinetics and toxicokinetics studies and could also be transposed to human urine for biological monitoring of workers exposed to TiO2-NPs.