SIMULTANEOUS STOPPED-FLOW DETERMINATION OF TETRACYCLINE AND DOXYCYCLINE IN SERUM BASED ON LANTHANIDE-SENSITIZED LUMINESCENCE

The intramolecular energy transfer from tetracycline and doxycycline t o europium ions was used for the first time for the fast simultaneous resolution of mixtures of these antibiotics in serum. The proposed met hod is based on the formation of the corresponding ternary chelates in the presence of thenoyltrifluoracetone. Mixtures of tetracycline and doxycycline in ratios between 5:1 and 1:7 can be satisfactorily resolv ed based on the initial rate and signal amplitude of the kinetic curve s obtained for each analyte and the use of the stopped-flow mixing tec hnique, with the aid of the proportional-equation method. The within- and between-assay precision data are close to 2%. The proposed method was applied to the direct determination of these antibiotics in serum with a mean recovery of 98.7% for tetracycline and 96.4% for doxycycli ne.