Stable and selective scintillating anion-exchange sensors for quantification of ⁹⁹TcO₄^- in natural freshwaters

New dual functionality scintillating anion-exchange resins were developed for selective determination of ⁹⁹TcO₄^- in various natural freshwater samples. Stable scintillating particles were formed by preparing the vinyl monomer 2-[4-(4'-vinylbiphenylyl)]-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (vPBD), starting with the commercial organic flour TBut-PBD and its subsequent copolymerization with styrene, divinylbenzene, 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 ⁹⁹TcO₄^- 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 SO₄^2- with up to 1000ppm and with up to 10ppm I^- and Cr₂O₇^2-. 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 5M HNO₃ for reuse at least four times without losing its chemical or optical performance. The detection limit was 1.45Bq which could be achieved by loading 45mL from well and tap water containing the maximum contaminant level (MCL) of ⁹⁹Tc (33Bq/L).