Submitted to: Talanta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/11/2004
Publication Date: 4/1/2004
Citation: Chen, G., Schneider, M.J., Darwish, A.M., Lehotay, S.J., Freeman, D.W. 2004. Europium-sensitized luminescence determination of oxytetracycline in catfish muscle. Talanta. 64. pp. 252-257. Interpretive Summary: Oxytetracycline is the only tetracycline drug approved by the U.S. Food and Drug Administration (FDA) to treat a series of bacterial diseases found in aquaculture. Its residue in fish might cause allergic reactions and microbial resistance in humans. This concern led the FDA and other regulatory bodies worldwide to establish an oxytetracycline tolerance in fish. Sensitive methods are therefore needed to monitor OTC residue levels. A time-resolved luminescence method was developed in this laboratory to determine oxytetracycline residues in farm-raised catfish. The drug was extracted from fish fillets, cleaned up by solid-phase extraction, treated with reagents, and measured by time resolved luminescence. The signal was shown to be proportional to the residue concentration. Excellent recoveries (higher than 90%) and a very low limit of detection (3-7 ng/g) were obtained. Incurred catfish samples were analyzed to demonstrate the method performance around 100 ng/g, the maximum residue level set by the European Union. With improved throughput, this highly sensitive and specific method can be useful to the fish farming industry and regulatory agencies around the world.
Technical Abstract: A europium-sensitized time-resolved luminescence (TRL) method was developed to determine oxytetracycline (OTC) in cultivated catfish muscle. Extraction of OTC from fish muscle was performed with pH 4.0 ethylenediaminetetraacetic acid (EDTA)-McIlvaine buffer and clean-up with hydrophilic-lipophilic balanced copolymer SPE cartridges. The eluate was used without further concentration for TRL measurement in pH 9.0 micellar tris(hydroxylmethyl)aminomethane (TRIS) buffer. Cetyltrimethylammonium chloride (CTACl) was used as surfactant and EDTA as a co-ligand. The excitation and emission wavelengths were set at 388 nm and 615 nm, respectively. The linear dynamic range was 0 - 1000 ng g-1 (R2 = 0.9995). The recovery was 92-112 % in the fortification range of 50 - 200 ng g-1 and the limits of detection (LOD) ranged from 3-7 ng g-1. Incurred catfish samples were used to demonstrate the performance of the method around 100 ng g-1, the European Union maximum residue level.