Trimethoprim-selective electrodes with molecularly imprinted polymers acting as ionophores and potentiometric transduction on graphite solid-contact Tânia S.C.R. Rebelo, Sofia A.A. Almeida, J. Rafaela L. Guerreiro, M. Conceição B.S.M. Montenegro c , M. Goreti F. Sales abstract Keywords: Trimethoprim Potentiometry Ion selective sensors Molecularly imprinted polymers Aquaculture water This work proposes a new biomimetic sensor material for trimethoprim. It is prepared by means of radical polymerization, having trimethylolpropane trimethacrylate as cross-linker, benzoyl peroxide as radicalar iniciator, chloroform as porogenic solvent, and methacrylic acid and 2-vinyl pyridine as monomers. Different percentages of sensor in a range between 1 and 6% were studied. Their behavior was compared to that obtained with ion-exchanger quaternary ammonium salt (additive tetrakis(p-chlorophenyl)borate or tetraphenylborate). The effect of an anionic additive in the sensing membrane was also tested. Trimethoprim sensors with 1% of imprinted particles from methacrylic acid monomers showed the best response in terms of slope (59.7 mV/decade) and detection limit (4.01 × 10 -7 mol/L). These electrodes displayed also a good selectivity towards nickel, manganese aluminium, ammonium, lead, potassium, sodium, iron, chromium, sulfadiazine, alanine, cysteine, tryptophan, valine and glycine. The sensors were not affected by pH changes from 2 to 6. They were successfully applied to the analysis of water from aquaculture. 1. Introduction Aquaculture is the production of aquatic organisms, such as the farming of fish, mollusks, crustaceans, amphibians and cultivating aquatic plants for man's use [1]. Industrial aquaculture is a rapidly growing industry in many developed and developing countries. A significant growth of food fish production has been observed over the past decade, due to the prevention or elimination of fish diseases. The introduction of veterinary medicines such as antimicrobials in the food production area has been the main responsible for this scenario [2]. Every year large quantities of antibiotics are administered to both humans and animals to treat and prevent diseases and infections. Antibiotics are also widely used at sub-therapeutic levels to growth- promoting. Often a high percentage of these antibiotics is excreted from dosed animals without metabolism or excreted in conjugated forms that can be readily converted back to the parent compounds [3]. Antibiotics are regarded as “pseudopersistent” contaminants due to their continual input into the ecosystem. Therefore, the occurrence of antibiotics in the environment has received considerable attention [4]. There is a growing interest about their presence, persistence and fate in the environment because low levels of antibiotics can favor the proliferation of antibiotic-resistant bacteria [5,6]. Antibiotic contaminants may disarray microbial ecology, increase the proliferation of antibiotic-resistant pathogens and pose threats to human health [3]. For food safety purposes, fish samples must be subject to rigorous and frequent controls that ensure that residues of antimicrobials are below the maximum legal levels [7]. Trimethoprim (TMP) belongs to the class of synthetic antibiotics and has the chemical structure presented in Fig. 1, which is used in human medicine and veterinary medicine. A thorough search in the literature revealed that liquid chromatography (HPLC) is the analytical method currently available to detect this antibiotic in water and wastewater. These liquid chromatographic methods (HPLC) are usually coupled to mass spectrometry (MS) [8], tandem mass spectrometry (MS/MS) [9], electrospray mass spectrometry (ESI-MS) [10] and electrospray tandem mass spectrometry (ESI-MS/ MS) [11] detection. They usually involve high cost and complex sample pre-treating procedures that could be used only for confir- mation of positive screening responses. Potentiometric sensors such as ion-selective electrodes (ISEs) may be used for screening a wide variety of organic and inorganic species.