Studies on the optimisation of optical response of scintillating optodes

Nine combinations of scintillating optode samples were prepared using three different matrix-forming polymers (cellulose triacetate (CTA)/polyvinyl toluene (PVT)/poly methyl methacrylate (PMMA)) plasticized with three different plasticizers (dioctyl phthalate (DOP)/tri-(2-ethylhexyl)phosphate (TEHP)/tri-(2-ethylhexyl)trimelitate (TOT)). One of these has been reported earlier for quantitative preconcentration and determination of α-emitting actinides. The absorption–emission spectra were used to optimise the type of plasticizer, amounts of primary scintillator (2,5-diphenyl oxazole (PPO)) and secondary scintillator (1,4-bis(2-methylstyryl)benzene (MSB)) in these optodes. The results suggest that TEHP is the best-suited plasticizer for all the matrix-forming polymers. Among them, the scintillator molecules immobilized in the TEHP plasticized PVT matrix produced higher α-scintillation pulse height than that in other matrices. However, the extraction efficiency of 241Am was found to be significantly lower (∼80%) in PVT/PMMA-based optodes as compared to CTA-based optodes (∼98%). Since the optode integrates preconcentration and signal generation steps, the PVT and PMMA polymers could not be used as matrix-forming polymer in the scintillating optode due to poor extraction efficiency of bis(2-ethylhexy)phosphoric acid (HDEHP) in these matrices. The TEHP plasticized CTA optode containing optimum amounts of scintillators and HDEHP was found to have optimum extraction efficiency for trivalent actinides, reusability and better α-scintillation efficiency than similar system developed earlier.