Fluorimetric method for the determination of uranium in natural waters

A method is described for the fluorimetric determination of uranium in natural waters. The limit of detection is 0.3 ppM. Ion-exchange is used to preconcentrate the uranium by a factor of 22 and separate it from quenching ions in the sample. The fluorescence is measured in a medium that is 1.35M in both sulphuric and phosphoric acids. The uranyl ions are excited by radiation of wavelength 280 nm and bandwidth 40 nm. The emitted signal is scanned from 470 to 510 nm. After spiking of the sample solution with a small volume of standard uranium solution, the fluorescence signal is scanned again and the uranium content of the sample calculated from the two readings. The coefficient of variation is 8.5% for determinations of U in a synthetic water sample having a uranium content of 1.9 ppM. Destruction of organic matter in the eluates gives 0.1 ppM detection limit.