URANIUM(VI) SPECIATION BY SPECTROSCOPY

The application of UV-Vis and time-resolved laser-induced fluorescence (TRLF) spectroscopies to direct speciation of uranium(Vr) in environm ental samples offers various prospects that have, however, serious lim itations. While UV-Vis spectroscopy is probably not sensitive enough t o detect uranium(VI) species in the majority of environmental samples, TRLFS is principially able to speciate uranium(VI) at very low concen tration levels in the nanomol range. Speciation by TRLFS can be based on three parameters: excitation spectrum, emission spectrum and lifeti me of the fluorescence emission process. Due to quenching effects, the lifetime may not be expected to be as characteristic as, e.g., the em ission spectrum. Quenching of U(VI) fluorescence by reaction with orga nic substances, inorganic ions and formation of carbonate radicals is one important limiting factor in the application of U(VI) fluorescence spectroscopy. Fundamental photophysical criteria are illustrated usin g UV-Vis and fluorescence spectra of U(VI) hydrolysis and carbonato sp ecies as examples.