Micelle-enhanced and terbium-sensitized spectrofluorimetric determination of gatifloxacin and its interaction mechanism

A terbium-sensitized spectrofluorimetric method using an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), was developed for the determination of gatifloxacin (GFLX). A coordination complex system of GFLX–Tb3+–SDBS was studied. It was found that SDBS significantly enhanced the fluorescence intensity of the complex (about 11-fold). Optimal experimental conditions were determined as follows: excitation and emission wavelengths of 331 and 547 nm, pH 7.0, 2.0 × 10−4 mol l−1 terbium (III), and 2.0 × 10−4 mol l−1 SDBS. The enhanced fluorescence intensity of the system (ΔIf) showed a good linear relationship with the concentration of GFLX over the range of 5.0 × 10−10 to 5.0 × 10−8 mol l−1 with a correlation coefficient of 0.9996. The detection limit (3σ) was determined as 6.0 × 10−11 mol l−1. This method has been successfully applied to the determination of GFLX in pharmaceuticals and human urine/serum samples. Compared with most of other methods reported, the rapid and simple procedure proposed in the text offers higher sensitivity, wider linear range, and better stability. The interaction mechanism of the system is also studied by the research of ultraviolet absorption spectra, surface tension, solution polarity and fluorescence polarization.