Radiochim. Acta 93, 219–224 (2005)  by Oldenbourg Wissenschaftsverlag, München Catechol functionalized aminopropyl silica gel: synthesis, characterization and preconcentrative separation of uranium(VI) from thorium(IV) By P. Metilda, J. Mary Gladis and T. Prasada Rao ∗ Regional Research Laboratory (CSIR), Trivandrum – 695 019, India (Received August 11, 2004; accepted in final form November 11, 2004) Catechol / Silica gel / Preconcentrative separation / Uranium / Soils and sediments Summary. A novel solid phase extractant is prepared by chemically immobilizing catechol with diazotized amino- propyl silica gel. The resulting catechol functionalized silica gel (CASG) was characterized by FTIR, and microanalysis and was used for selective enrichment of uranium(VI) from other inorganic ions. The optimum pH range for maximum sorption of uranium(VI) and thorium(IV) was found to be in the range 3.5–6.0. The above actinides were eluted with 10 cm 3 of 1.0 mol dm −3 HCl and determined by using an Arsenazo III spectrophotometric procedure. The calibration graph was rectilinear over the uranium(VI) concentration in the range 2–100 μ g dm −3 with a relative standard deviation of 2.15% (for 25 μ g of uranium(VI) present in 1.0 dm 3 of sample). The validation of the developed preconcentration procedure was carried out by analyzing marine sediment (MESS-3, NRC, Canada) and soil (IAEA soil-7, Austria) reference materials. The developed preconcentration method enables a simple instruments like a spectrophotometer gave comparable values of uranium(VI) to that of standard induc- tively coupled plasma-mass spectrometric values during the analysis of real soil and sediment samples. Introduction Solid phase extraction (SPE) is now routinely used in dif- ferent analytical [1], chromatographic [2, 3], clinical [4, 5], pharmaceutical [6, 7], environmental [8], industrial [9] and agricultural [10] fields. SPE offers several major advan- tages over the classical liquid–liquid extraction (LLE) tech- nique and include [11] the fast, simple and direct appli- cation in very low (mm 3 ) to high volumes (dm 3 ) without any sample loss and no waste generation as practiced in the LLE method. Moreover, SPE offers higher enrichment factors, saves cost and time, can be interfaced with ma- jor chromatographic technique either in the form of offline or online modes. More importantly SPE is environmentally friendlier. The essential requirements for a sorbent in SPE are (i) thermal, chemical and mechanical stability, (ii) high sur- *Author for correspondence(E-mail: tprasadarao@rediffmail.com). face area (> 100 m 2 /g), (iii) appropriate pore size (> 20 Å), (iv) quantitative sorption and elution, (v) kinetically faster sorption and desorption mechanism, (vi) regenerability, (vii) good selectivity and (viii) no swelling [12]. Inorganic supports such as silica gel, alumina, titania, zirconia, zeo- lite, ZnO and clay generally meet these requirements and have been widely used, although organic polymers have also been extensively investigated. Silica gel possess silanol groups on its surface resulting in very low extraction of inor- ganic ions [13, 14]. Chelate functional groups are physically sorbed on silica gel and has been used for improved enrich- ment of inorganic ions compared to bare silica gel [15, 16]. The main drawback of physical sorption is the lack of reusability. On the other hand, the chemical immobilization of silica gel by certain organic chelating functional groups offers selectivity, reusability and high retention capacity. Furthermore, the chemical bonding of functional groups offers a unique advantage that the grafted molecule detach- ment is prevented due to strong covalent bonding of the molecule to the SPE support [17]. The intense current interest in uranium arises from its known toxicity and the possibility of human exposure to it. Such exposure can cause acute renal failure resulting in a fatality or minor damage to liver [18]. Hence, WHO rec- ommends the safe limit for uranium(VI) in drinking water at ∼ 5 ng cm −3 . This paper reports (i) chemical immobiliza- tion of catechol onto aminopropyl silica gel, (ii) charac- terization of catechol functionalized aminopropyl silica gel (CASG), (iii) preconcentrative separation of uranium(VI) using CASG and (iv) application to the analysis of soil and sediment samples. Experimental Instrumentation A Hitachi-220 microprocessor controlled double beam spec- trophotometer (Hitachi, Japan) was used for monitoring actinides during preconcentration experiments. A LI-120 digital pH meter (ELICO, India) was used for pH meas- urements. IR spectra were recorded in the frequency range 4000–400 cm −1 by KBr pellet method using a Magna FTIR- 560 spectrometer (Nicolet, USA). Microanalysis studies