Cloud Point Extraction of Metal Oxide Nanoparticles in Water Samples Identified by Raman Spectroscopy and Quantified by Atomic Absorption Spectroscopy

Engineered nanoparticles have been shown to affect the growth of living organisms in freshwater such as lakes and rivers. It is important to acquire a suitable technique to identify nanoparticles and quantify them. Raman scattering offers the advantage of analyzing micro-scale nanoparticle species which is the maximum amount available in aquatic environment. In this project, cloud point extraction (CPE) with Raman spectroscopy and atomic absorption spectroscopy was applied to the analysis of titanium dioxide nanoparticles (TiO₂ NPs) and zinc oxide nanoparticles (ZnO NPs) in water and environmental water samples. The non-ionic surfactant Triton X-114 was used to extract the metal oxide nanoparticles from water. The sample was centrifuged to collect the surfactant, followed by Raman spectroscopy of the surfactant phase. NPs were hydrolyzed in concentrated H₂SO₄, and then diluted to give samples for flame AA. Several CPE factors such as surfactant concentration, pH, incubation temperature, and incubation time were optimized. Method performance was characterized in terms of the smallest concentration of NPs detected, by the selectivity over metal ions, and by the sensitivity of Raman spectroscopy to identify small quantities of NPs in mixtures.