Trimethoprim (TMP) is widely used worldwide as an antibacterial drug to prevent and treat a variety of bacterial infections in humans and animals, which mainly include urinary, intestinal, and respiratory infections. It has been estimated that around 50 to 70% of the drug is excreted from the body in its original form and accumulates gradually in the aquatic environments, which causes several ecological and health risks such as antibiotic resistance, bioaccumulation in the food chain, and disruption of microbial communities [1]. Consequently, the development of accurate and sensitive analytical methods for the detection and determination of TMP in environmental water and wastewater samples is of utmost priority. Among various analytical methods used to date for this purpose, electrochemical sensors offer several benefits as they are fast, low-cost, and user-friendly [2]. Herine, a novel disposable electrochemical sensor for TMP is introduced based on a pencil graphite electrode (PGE) modified with polyphloroglucinol. Cyclic voltammetry was employed for an in-situ electropolymerization of phloroglucinol and the conditions were optimized using a multivariate strategy. Plackett–Burman experimental design was used for the screening step to evaluate the influence of the parameters affecting the analytical response of the sensor such as pH, loading time, and stirring rate, as well as the factors which impact on the polymerization step including monomer concentration, pH, scan rate, and cycle number. Next, central composite design was employed to optimize the influential operating parameters. Under the optimum operating conditions, a calibration plot was constructed in the concertation range of 0.03 to 200 μM of TMP, which showed to be linear in the range of 0.10-100.00 μM. As well, the limits of detection (LOD) and quantification (LOQ) were obtained to be 0.03 and 0.1 μM, respectively. Moreover, the repeatability and reproducibility were assessed in terms of RDS% and achieved to be 18% and 4%, respectively; which reveals the necessity of being disposable. Finally, to show the practical applicability of the sensor to real samples, spiked hospital and cattle farm wastewater samples were subjected to analysis using the proposed sensor, which yielded the recoveries in the range 98.3-104.0%.

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