Determination of flunixin by sensitized terbium fluorescence in the presence of surfactant micelles

The effect of surfactant micelles and the second ligand on the efficiency of energy transfer in the Tb³⁺–flunixin complex was studied. The fluorescence intensity of the Tb³⁺–flunixin complex was shown to 100-fold increase in the presence of Tween 80 micelles and the second trioctylphosphine oxide ligand. A procedure for the fluorimetric determination of flunixin in the Flunex drug product (NITA-FARM, Saratov, Russia) was developed. The linearity range of the calibration curve was from 1 × 10^–7 to 1 × 10^–4 M, r ² = 0.991, and the limit of detection was 4 × 10^–8 M (3σ).