Reversed-phase liquid chromatographic determination of uranium based on its ternary complex with fluoride and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol. New chromatographic probe for the detection of fluoride on C18 stationary phase surface

Optimum conditions for the reversed-phase liquid chromatographic separation of uranium as U(VI)–F−–(5-Br-PADAP) [5-Br-PADAP is 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol] ternary complex on the end-capped C18 column were evaluated. The developed sensitive, selective and versatile method allows to determine uranium in the wide concentration range 0.2–120.0 μg ml−1 (detection limit, DL, is 0.15 μg ml−1 for 20 μl loop). Solvent mixture, acetonitrile+water (65+35, v/v) containing fluoride in concentration 3×10−3 mol l−1 (pH 5.5) was used as eluent. Double action of fluoride present in eluent — as stabilising agent of the ternary system and modifier of the stationary phase was evaluated. In order to prove appearance of the modifying effect of fluoride on the stationary phase the new chromatographic probe — system Zr(IV)–(5-Br-PADAP)/Zr(IV)–F−–(5-Br-PADAP) was introduced as a tool for the detection of F− presence on the surface.