Microchim Acta 154, 109–114 (2006) DOI 10.1007/s00604-005-0478-5 Original Paper Use of Benzoylthiourea Immobilized on Silica Gel for Separation and Preconcentration of Uranium(VI) Melek Merdivan  , Serap Seyhan, and Cem Gok Chemistry Department, Faculty of Science and Arts, Dokuz Eylul University, Izmir 35160, Turkey Received September 1, 2005; accepted November 30, 2005; published online March 9, 2006 # Springer-Verlag 2006 Abstract. Benzoylthiourea immobilized on silica gel was prepared by two-step post-synthesis modification. The capacity of the chelating silica gel, which was characterized by FTIR, was 3.21 mmol  g 1 . The separation and enrichment of uranium(VI) from solu- tions was investigated. Effective extraction conditions were optimized in both batch and column methods prior to determination by spectrophotometry using arsenazo(III). The optimum pH range for quantitative adsorption is 4–7. Quantitative recovery of U(VI) was achieved by stripping with 0.1 mol  L 1 HCl. The sorption capacity of modified silica gel was 0.85 mmol  g 1 uranium(VI). Recovery of U(VI) was 99.1  2.3% with a detection limit of 2 mg  L 1 . The preconcentration factor was 250, and the relative stan- dard deviation was 1.53% for a 1 mg  L 1 U(VI) solu- tion. The method was used for the determination of uranium in synthetic samples and a soil sample. Key words: Benzoylthiourea; silica gel; preconcentration; uranium(VI). Chelating resins are frequently used in analytical chemistry for the enrichment of metal ions and their separation from interfering constituents prior to their determination by an instrumental method. Appropriate chelating reagents can be immobilized onto polymeric supports [1] and used for the solid phase extraction of metal ions from aqueous solutions. Recently, chem- ically modified sorbents have been developed and used in the extraction of metals from a multicompo- nent mixture in various analytical applications [1–3]. A number of chelating sorbents were prepared by incorporating various functional groups (e.g. o-amino- benzoic acid [4], iminodiacetic acid [5], 1,2-diphenyl- ethanolamine [6], etc), and their analytical properties were investigated. The synthesis effort was focused on the modification of ordered mesoporous silicas in order to achieve highly selective materials for the pre- concentration and separation of heavy metal ions [7, 8]. Uranium is a prominent element whose isotopes occur in various concentrations and oxidation states in radioactive waste and geological materials, ura- nium(VI) being the most prominent one. So far, this element has been selectively extracted by liquid– liquid extraction, e.g. using quaternary ammonium salts [9, 10], thenoyltrifluoroacetone in xylene [11] or a mixture of -diketones and crown ethers [12]. Standard cation exchangers allow the separation of uranium from aqueous solutions, but these materials are exhausted quickly in the presence of other metal ions due to non-selective binding. Chemically modified or impregnated silica, active carbon and Amberlite XAD resins have recently been used to achieve highly selec- tive materials for the preconcentration and separation of this ion. Chemically modified and impregnated  Author for correspondence. E-mail: melek.merdivan@deu. edu.tr