Solid Phase Extraction and Determination of Tetracycline Using Gold Nanoparticles Stabilized in a Polymethacrylate Matrix

A polymethacrylate matrix (PMM) is proposed for the solid-phase extraction and determination of tetracycline (TC). The study of the influence of medium acidity, temperature, and contact time on the extraction of tetracycline by PMM showed that tetracycline is extracted by the matrix in the form of a singly charged anion H₂TC^-, within the pH range of 8.9-9.7, with distribution coefficients reaching (5-6) × 10³ mL/g. Following the extraction process using PMM and PMM-Au⁰, the direct determination of tetracycline in the solid phase is possible without an elution step. This is achieved by using as the analytical signal both the intrinsic absorption and the instrumentally measured peak area of the anionic form of tetracycline, H₂TC^-, in the matrix, with detection limits of 0.03 and 0.01 mg/L, respectively, and the fluorescence of tetracycline in PMM and PMM-Au⁰, with detection limits of 0.001 and 0.005 mg/L, respectively. The applicability of the digital colorimetry method for the quantitative determination of tetracycline based on its fluorescence in the solid phase is demonstrated. Methodologies for the determination of tetracycline using PMM and PMM-Au⁰ were developed and tested in the analysis of river and bottled water samples, biological fluid, as well as honey and milk samples.