Europium-sensitized luminescence determination of oxytetracycline in catfish muscle.

An 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 solid phase extraction (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 and 615nm, respectively. The linear dynamic range was 0-1000ngg(-1) (R(2)=0.9995). The recovery was 92-112% in the fortification range of 50-200ngg(-1) and the limits of detection (LOD) ranged from 3 to 7ngg(-1). Incurred catfish samples were used to demonstrate the performance of the method around 100ngg(-1), the European Union maximum residue level.