Radionuclide Sensors Based on Chemically Selective Scintillating Microspheres: Renewable Column Sensor for Analysis of99Tc in Water

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Abstract
A method for chemically selective radiometric sensing of non-γ-emitting radionuclides in solution is described. Using scintillating microspheres with selective radionuclide uptake properties, radiochemical separation and radiometric detection steps are integrated within a sensor device. These microspheres are loaded into a renewable minicolumn that serves to capture, preconcentrate, and separate radionuclides. The preconcentrating minicolumn also localizes and retains radionuclides within a detector of well-defined geometry and emits a photometric signal. The sensor material in the column can either be regenerated with eluent chemistries or be renewed by fluidic replacement of the beads. The latter method allows the use of materials that bind analytes irreversibly or are unstable under regeneration conditions. Radionuclide-selective scintillating microspheres were prepared by coimmobilization of scintillating fluors and selective organic extractants within the pores of an inert polymeric support. Preparation and characterization of microspheres, and their use for selective quantitative sensing of 99Tc(VII), is described in detail. A sensor-based procedure for 99Tc(VII) analysis was developed and successfully applied toward the determination of 99Tc(VII) in groundwater samples from the Hanford site, using standard addition techniques for quantification. Using a 50-mL sample volume and signal accumulation time of 30 min, the detection limit for 99Tc(VII) was 0.37 dpm/mL (9.8 pg/mL).