Lanthanide-Sensitized Luminescence Instrumentation and Methods for Analysis of Tetracycline and Fluoroquinolone Residues in Foods

Lanthanide-sensitized luminescence (LSL) is highly valuable for analysis of two classes of antibiotic drugs: tetracyclines (TC) and (fluoro)quinolones (FQ). In theory, efficient intrachelate energy transfer enhances LSL's sensitivity and specificity. In practice, time-domain measurement effectively rejects short-life spectroscopic interferences. To take full advantage of LSL, a portable luminescence spectrometer was developed and applied to analysis of TC and FQ residues in food matrices. Implementation of light emitting diode excitation and photomultiplier tube gating technique resulted in improved performance especially signal-to-background ratio. Two applications are demonstrated in this work: quantitation of oxytetracycline, the most prominent antibiotic in shrimp aquaculture, with 12.7 ng/g limit of quantification; and binary screening of four FQs registered in European Union in caprine milk: danofloxacin, flumequine, and enrofloxacin plus its metabolite ciprofloxacin at their maximum residue limits at 30, 50, and 100 ng/g, respectively.