Selective separation and quantification of hematite nanoparticles and ionic iron via cloud point extraction and flame atomic absorption spectrometry

Abstract

The increasing use of nanomaterials (NMs) in materials science, health, and technology has raised concerns regarding their environmental distribution, stability, and toxicity. Iron oxide nanoparticles (IONPs) are notable for their widespread applicability and reactivity. In this context, developing simple, rapid, and environmentally friendly methods for separating and quantifying them is essential. This study proposes a cloud point extraction (CPE) method for the selective separation of hematite nanoparticles (HemNPs) from ionic iron, allowing for their subsequent quantification using flame atomic absorption spectrometry (FAAS). The synthesized HemNPs utilized in this study exhibited 61% crystallinity, forming pseudo-spherical aggregates with a size of 68 ± 15 nm, an individual particle size of 5 ± 1 nm, and a hydrodynamic diameter of 10 ± 1 nm. The optimized CPE conditions involved Triton X-100 (5% v/v) as the nonionic surfactant, EDTA as the complexing agent, a pH of 5, and 0.15 mol L⁻¹ of CaCl₂ to lower the cloud point temperature. Under these conditions, HemNPs were effectively separated, with recoveries ranging from 85.7% to 103.4% and an enrichment factor of 5. The method was also applied to real water samples, where HemNPs were not quantified, and spike recovery tests showed values above 70%, demonstrating the method's efficiency. To the best of our knowledge, this is the first report combining CPE with FAAS for the determination of HemNPs, providing a cost-effective, solvent-free, and robust alternative for monitoring iron-based nanomaterials in aqueous matrices.