Abstract: A selective and sensitbe sensitized chemiluminescence (CL) method for the determination ofGatifloxacin(GFLX) is described.The method is based on Tb³⁺ sensitized chemiluminescence of the Tb³⁺-GFLX-Ce(Ⅳ)-SO₃^2- system since CLfor the binary Ce(Ⅳ)-SO₃^2- system is weak, while CL is enhanced when Tb³⁺-GFLX is added to the Ce(Ⅳ)-SO₃^2- system.The possible mechanism of the CLreaction maybe that Ce(Ⅳ) can oxidize HSO₃^- to a hydrogen-sulfite radical HSO₃, then HSO₃ radicals produce S₂O₆^2-,S₂O₆^2- will form the excited intermediate product SO₂. The energy of SO₂ is mainly transferred to Tb³⁺-GFLX, and the CLspectrum shows a characteristic emission of Tb³⁺.The re1ationship between the CLin-tensity and the concentration of GFLXis linear in the range of 2.0 × 10^-8-1.0×10^-6 mol/L, and the de-tection limit is 3.5 × 10^-9 mol/L.The relative standard deviation(RSD) for 11 independent determinationsof 1.0×10^-7 mol/L GFLX was 3.2%.Common excipient starch was used in pharmaceutical preparationand most of metal ions do not interfere with the determination of GFLX.GFLXin urine can be analyzeddirectly after appropriate dilution of the samples, and the analytical result is satisfactory.

Key words: Gatifloxacin, Terbium, Chemiluminescence, Energy transfer, Flow injection