Nanomagnets based on activated carbon/magnetite nanocomposite for determination of endocrine disruptors in environmental water samples

Abstract

Endocrine disruptors (EDs) have been defined as exogenous compounds that alter the endocrine system's normal functioning. These micropollutants have the potential of entering water bodies, becoming an environmental issue of increasing concern. Since EDs occur at very low concentrations (μg L-1 to ng L-1), efficient extraction and clean-up steps are required before their detection. Thus, a magnetic nanosorbent was synthesized in this work by modification of powder activated carbon with magnetite nanoparticles (AC/Fe3O4). The nanosorbent was applied in magnetic solid-phase extraction (MSPE) of bisphenol A (BPA) and 17α-ethinylestradiol (EE2) in environmental water samples, prior to determination by HPLC-UV. The composite was characterized by X-ray diffraction, thermogravimetric analysis (TGA), spectroscopy electron microscopy, Mössbauer spectroscopy, Brunauer-Emmet-Teller analysis, and zeta potential measurements. TGA data showed that decomposition of the carbon structure in the composite (AC/Fe3O4) occurs at 400–550 °C, corresponding to 25% of the sample content. The magnetite corresponds to 59% of residual mass, and the synthesized magnetic adsorbent showed a specific surface area approximately 8 times greater when compared to pure activated carbon. The pHpzc obtained for AC/Fe3O4 was 5.18. Properties of the composite such as high specific surface area and paramagnetism resulted in an efficient adsorbent that provided a good recovery for both EDs investigated (80.91% for BPA and 56.72% for EE2). After optimizing MSPE conditions, the established adsorption/desorption time was 60 s; the adopted elution solvent was metanol:acetonitrile (50: 50% v/v), with a volume of 750 µL. Other optimum conditions obtained were: 20 mg of nanosorbent and sample volume of 750 μL at pH 10.5. The analytical method has a linear range from 0.08 to 5.0 µg mL−1 for both analytes, with correlation coefficients equal to 0.9973 and 0.9996 for BPA and EE2, respectively. The limit of detection and limit of quantification were 0.10 and 0.80 µg mL−1 respectively for both analytes. In addition, interday and intraday accuracy assays obtained relative standard deviation and relative error values below 15%. The method was successfully applied in the determination of BPA and EE2 in river water. High BPA and EE2 concentrations (0.418 ± 0.017 µg mL−1 and 1.330 ± 0.040 µg mL−1 for BPA and EE2, respectively) were detected in the Lenheiro stream, which receives untreated domestic sewage. The main advantage of AC/Fe3O4 was the simplicity of the synthesis compared to other magnetic materials described in the literature, besides being economical, fast, and environmentally friendly, since waste-based carbonaceous materials can be used as a precursor to AC.