Rapid Screening of Oxytetracycline Residue in Fish Muscle by Dispersive Liquid-Liquid Microextraction and Europium-Sensitized Luminescence

A screening protocol was developed for oxytetracycline (OTC) residue in catfish muscle based on dispersive liquid-liquid microextraction (DLLME) and europium-sensitized luminescence (ESL). The analyte was extracted in HCl-ethylenediaminetetraacetic acid (EDTA)-acetonitrile, cleaned up by DLLME in water-acetonitrile-hexane-CH2Cl2, and detected by ESL using a portable luminescence photometer. A threshold was established at T = x 2 − 3σ2, where x 2 and σ2 were mean and standard deviation of ESL signals of catfish muscle samples (n = 20) spiked at 2 μg g−1, the tolerance set by the US Food and Drug Administration (FDA). Among 48 samples randomly spiked with OTC at 0–4 μg g−1, 46 were screened correctly without false negative, and 2 negatives were classified as presumptive positives. This reliable method cut usage of chlorinated solvent to 0.75 mL, reduced cost, and improved sample throughput.