Determination of non-steroidal anti-inflammatory drugs in water samples using a graphene oxide/Fe ₃ O ₄ /polyoxometalate composite as a sorbent

The detection of nonsteroidal anti-inflammatory drugs (NSAIDs) in water samples is of critical importance due to their adverse effects on aquatic ecosystems, including toxicity to fish and invertebrates, and the potential risks to human health through contaminated drinking water sources. Precisely monitoring their content is crucial yet difficult due to their complex matrix and trace concentrations. This study presents a magnetic tri-component composite that was prepared based on immobilized Keggin-type polyoxometalate (H₄SiW₁₂O₄₀ (SiW)) and Fe₃O₄ nanoparticles on graphene oxide (GO) sheets (GO/Fe₃O₄/SiW) through a hydrothermal synthetic method. This composite benefitted from the abundant delocalized π-electron systems from its GO support and the oxygen-rich surface from the functional groups of GO and SiW moieties, resulting in strong affinity toward target analytes through various mechanisms like π-stacking, hydrogen bonding, and electrostatic interactions. Along with the above-mentioned advantages, the Fe₃O₄ magnetic nanoparticles of the GO/Fe₃O₄/SiW composite showed the potential to be employed as a very effective sorbent for the magnetic solid-phase extraction (MSPE) of five types of NSAIDs (ibuprofen, diclofenac, naproxen, tenoxicam, and meloxicam) with different functional groups. A high-performance liquid chromatography coupled with an ultraviolet detector (HPLC-UV) was established, which exhibited good linearity ranges (0.03-300 ng mL^-1) and limit of detection ranges (0.01-0.03 ng mL^-1), which are significantly lower than those of many previously reported sorbents. To assess the method's accuracy, the inter-day and intra-day relative standard deviations (RSDs%) for five types of NSAIDs were measured, ranging from 3.7% to 5.0% across three concentration levels (0.1, 5, and 100 ng mL^-1). Moreover, the method achieved high recoveries ranging from 97.1% to 100.0%, demonstrating its outstanding efficiency in extracting NSAIDs. These enhancements highlight the composite's potential for reliable, sensitive, and rapid environmental monitoring of pharmaceutical pollutants at trace levels.