Spinel ZnFe ₂ O ₄ Nanoparticles Doped with Ba ² ⁺ for High-Performance Cu(II) Extraction via <i>d</i> -SPE–FAAS

In this study, a dispersive solid-phase extraction (<i>d</i>-SPE) method was developed and characterized using Ba-doped ZnFe₂O₄ spinel nanoparticles for the selective preconcentration and determination of Cu-(II) ions in environmental- and food-based matrices. The structural features of the nanosorbent were thoroughly investigated using SEM, SEM-EDX, XRD, and FTIR techniques. The integration of Ba² ⁺ into the spinel lattice structure enhanced the adsorbent's surface reactivity, and the material is therefore presented as a high-surface-area spinel sorbent, which contributed to the efficient and selective retention of Cu-(II) ions. Following the optimization of extraction parameters (pH 9.0, 40 mg of sorbent, 0.3 mL of HNO₃, 60 s vortex for adsorption, and ultrasonic mixing for desorption), quantification was carried out using flame atomic absorption spectrometry (FAAS). The method exhibited excellent analytical performance, achieving a limit of detection (LOD) of 0.67 ng mL^- ¹, a wide linear dynamic range of 5.0-300 ng mL^- ¹, and a correlation coefficient (<i>R</i> ²) of 0.9992. The developed <i>d</i>-SPE-FAAS method achieved an LOD improvement factor of 62, along with an enhancement factor of 29 and a classical preconcentration factor of 30. In addition, a Langmuir isotherm study at pH 9.0 indicated a maximum adsorption capacity of 104.2 mg g^- ¹, confirming the affinity of the Ba-doped ZnFe₂O₄ sorbent for Cu-(II). Applicability of the method was evaluated using real samples, including green tea infusions, tap water, and domestic wastewater obtained from the General Directorate of VASKİ (Van Water and Sewerage Administration). Quantitative recoveries ranging from 94% to 106% were obtained in real matrices, demonstrating the method's accuracy and reliability in complex sample compositions. The developed <i>d</i>-SPE-FAAS protocol provides a simple, sensitive, and cost-effective approach for determining trace levels of Cu-(II), exhibiting strong potential for routine copper monitoring in both environmental and food-derived samples.