Determination of titanium speciation in consumer plastics by Raman microspectroscopy

The main component of objects made of plastic is an organic polymer matrix, but plastics also contain a wide range of other chemicals, such as additives, processing aids and unintentionally added substances. At present, the scientific and regulatory communities face challenges due to the lack of access to basic information on their quantity and identity, which is crucial in relation to potential toxicity, management, recycling, environmental fate and resource uses. Moreover, an additional problem is that some additives, such as titanium oxide (TiO₂), can be present in different crystallographic forms, which makes it necessary to characterise not only the total amount of titanium present, but also its polymorph. Titanium dioxide is widely used in plastics and is found in two different polymorphs: anatase and rutile. Here we highlight several advantages of Raman microspectroscopy over conventional Raman spectroscopy in the detection of TiO₂ in plastics and synthetic textiles. A main advantage derives from a better signal-to-background ratio due to its small sampling volume. In this study, it was possible to detect the TiO₂ form at concentrations as low as ∼ 450 mg kg⁻¹. Furthermore, we demonstrate that the choice of the less used 405 nm laser for Raman spectroscopy could overcome the unwanted fluorescence background in some cases. We found the presence of anatase in all textiles analysed and rutile in virtually all consumer plastic samples.