Time-Resolved Laser-Induced Fluorescence Studies of Uranium/Sodium Dodecyl Sulfate Interactions

Abstract

Time-Resolved Laser-Induced Spectrofluorometry (TRLIS) is a very sensitive and selective technique for uranium(VI) (UO22+) determination based on laser excitation followed by temporal resolution of the fluorescence signal. This analytical technique has been used for several years for uranium analysis in various matrices in the nuclear fuel cycle, in the environment, and in the medical field. Limits of detection (LODs) for uranium are now lower than the ng/L range, and trends are leading towards direct analysis for on-line analysis via fiber optics and optode in the above fields. However, aside from elementary analysis, TRLIS possesses an interesting characteristic, namely, its capability of giving both spectral information with the fluorescence spectrum (wavelength shifts, peaks ratio modifications) and temporal information with the fluorescence lifetime (characterization of the molecular environment). These features have been used to study the interaction (complexation, quenching, energy transfer) between (UO22+) and ions(Fe2+, Ag+, Cl−, etc.) or organic molecules, but very few investigations have been carried out with surfactants and uranium, Surfactants are organic compounds which possess both a polar or ionic head group and a nonpolar tail. Depending upon the nature of the head group, they can be classified as cationic, anionic, or nonionic surfactants. When the surfactant is present at concentrations greater than its critical micellar concentration (CMC), aggregates called micelles are formed, into which organic compounds are solubilized. Micelles composed of ionic surfactants exhibit a high surface charge, and counter ions (ions of opposite charge to the surfactant) will bind to the surface of the aggregate.