Thermal Synthesis of Reduced Graphene Oxide-Natural Phosphate for Hydroxychloroquine Detection in Urine, Wastewater, and Pharmaceutical Samples

The presence of hydroxychloroquine (HCQ) residues in the environment and biological systems has raised global concern. This necessitates the development of sensitive methods for its detection in complex matrices. This study presents a novel, green, and low-cost sensing platform for detecting HCQ using a carbon paste electrode (CPE) modified with a composite of natural phosphate (NPh) and reduced graphene oxide (rGO-NPh@CPE). It was thermally treated to reduce graphene oxide on the surface of phosphate particles. The presence of graphene oxide and its reduced form was confirmed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR), while scanning electron microscopy (SEM) revealed exfoliated graphene sheets dispersed within the phosphate matrix. Additionally, energy-dispersive X-ray spectroscopy (EDS) confirmed the elemental composition and successful incorporation of carbon into the composite. The sensor exhibited adsorption-controlled behavior and showed a linear response over two ranges: 1.0 × 10 –7 to 1.0 × 10 –6 mol l −1 and 1.0 × 10 –7 to 1.0 × 10 –5 mol l −1 , with a detection limit of 50 nM. Interference studies demonstrated high selectivity, with recovery rates ranging from 97.2% to 102.0% in the presence of interfering species. The sensor was successfully applied to real samples, with recovery values between 97.0% and 100.7%.