Stable and selective scintillating anion-exchange sensors for quantification of 99 TCO 4  in natural freshwaters Ayman F. Seliman a, * , Kerttuli Helariutta b , Szymon J. Wiktorowicz c , Heikki Tenhu c , Risto Harjula b a Department of Analytical Chemistry and Environmental Control, Atomic Energy Authority, Egypt b Laboratory of Radiochemistry, PL 55, University of Helsinki, FI-00014, Finland c Laboratory of Polymer Chemistry, PL 55, University of Helsinki, FI-00014, Finland article info Article history: Received 28 May 2013 Received in revised form 16 July 2013 Accepted 30 July 2013 Available online 4 September 2013 Keywords: 99 TcO 4  Flow cell Scintillating sensor Freshwaters abstract New dual functionality scintillating anion-exchange resins were developed for selective determination of 99 TcO 4  in various natural freshwater samples. Stable scintillating particles were formed by preparing the vinyl monomer 2-[4-(4 0 -vinylbiphenylyl)]-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (vPBD), starting with the commercial organic flour TBut-PBD and its subsequent copolymerization with styrene, divinylben- zene, and p-chloromethylstyrene mixture. To integrate the radiochemical separation and radiometric detection steps within the same bead, the chloromethyl groups of the scintillating resins were subjected to amination reactions with dioctylamine (DOA) and trioctylamine (TOA). On-line quantification of 99 TcO 4  was achieved by packing the scintillating anion-exchange resin into Teflon tubing for quantification by a flow scintillation analyzer (FSA). The two functionalized resins were selective for pertechnetate over the common anions in natural freshwaters, especially Cl  and SO 4 2 with up to 1000 ppm and with up to 10 ppm I  and Cr 2 O 7 2 . The uptake efficiency of the TOA sensor decreased from 97.88% to 85.08% in well water and river water, respectively, while the counting efficiency was almost constant (69.50%). The DOA performance showed lower efficiency in the two water types relative to TOA. On the other hand, the DOA sensor could be regenerated by 5 M HNO 3 for reuse at least four times without losing its chemical or optical performance. The detection limit was 1.45 Bq which could be achieved by loading 45 mL from well and tap water containing the maximum contaminant level (MCL) of 99 Tc (33 Bq/L). Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Technetium is generated in large quantities as a fission product in the making of nuclear weapons and by irradiation of 235 U- enriched fuel during production of commercial power. The most abundant Tc isotope in wastes, 99 Tc, has a high fission yield (approximately 6%) and a long half-life (2.13  10 5 years) (Um et al., 2011) Its inventory is expected to increase if nuclear power gen- eration is emphasized in response to concerns for the use of fossil fuel and emission of atmospheric greenhouse gases (Gu et al., 2011). Although the Tc valence state can vary from VII to III, Tc(VII) in the form of the pertechnetate oxyanion (TcO 4  ) is the most stable in natural oxic environments. It is highly soluble in water but poorly retained by sediments and thus readily transported in the subsurface (Boggs et al., 2011). Investigating Tc species stability, solubility, and mobility is essential for assessing their behavior and impact in contaminated environments. To achieve this goal, suit- able measurement methods for quantification of the 99 TcO 4  con- centration in the environment is important, but the measurement process is complicated by several factors especially the lack of any gamma emission, radiometric interference during beta detection, and isobaric interference during ICP-MS measurement (Butterworth et al., 1995). To overcome these difficulties, a highly selective extractant or anion-exchange resin for 99 TcO 4  separation is required, which concentrates Tc in the presence of interfering anions (e.g. chloride (Cl  ), sulfate (SO 4 2 ), nitrate (NO 3  ), bicarbonate (HCO 3  ), and chromate (Cr 2 O 7 2 )) of the natural water samples. The first trial to accomplish radionuclide separation by anion- exchange resin with scintillating properties was reported over 40 years ago (Heimbuch et al., 1965). Other investigators used two different techniques, based on the same principle, to measure 99 Tc in various matrices. DeVol et al. (2001) and Egorov et al. (1999) co- immobilized the organic scintillating fluors 2,5-diphenyloxazol (C 15 H 11 NO) (PPO) and 1,4-bis(4-methyl-5-phenyloxazol-2-yl) * Corresponding author. E-mail address: aymanseliman@yahoo.com (A.F. Seliman). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad 0265-931X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2013.07.025 Journal of Environmental Radioactivity 126 (2013) 156e164