Diclofenac sodium

Synthesis of DF-CMK-3: diclofenac sodium (Sigma-Aldrich, St. Louis, MO, USA) and distilled water (Merck, Darmstadt, Germany) were used during synthesis.
Electrochemical measurements: Appropriate volumes of 1 M CH₃COONH₄ and 1 M HCl (Sigma-Aldrich, St. Louis, MO, USA) were used to obtain 1 M buffer solution (CH₃COONH₄, CH₃COOH, and NH₄Cl) with a pH of 5.6. The standard solutions of Fe³⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Sb³⁺, Pb²⁺, NO₂⁻, NO₃⁻, Cl⁻, and Triton X-100 (Merck, Darmstadt, Germany) were used to study the selectivity of the proposed procedure, and 96% ethanol solution (Merck, Darmstadt, Germany) was used to prepare 10 and 1 mM roxarsone (ROX, AK Scientific, Union City, CA, USA). The ROX solution with a concentration of 0.01 mM was prepared daily in 0.1 M PBS buffer with a pH of 7.2. The wastewater samples were obtained from the Municipal Water Supply & Waste Water Treatment Company Ltd. (Lublin, Poland), while river water samples were collected from the Vistula River (Sandomierz, Poland). The ROX spiked samples were filtered (0.22 µm Millipore filter).