Trace-level determination of Cs+ using membrane-based ion-selective electrodes

A membrane-based ion-selective electrode (ISE) has been developed for the trace-level determination of Cs' in aqueous samples. A systematic evaluation of several ionophores was performed, examining the effect of membrane plasticizer and ion exchanger on sensor selectivity. Poly(vinyl chloride) (PVC)-based ion-selective membranes of conventional composition containing calix[6]arene hexaacetic acid hexaethylester as ionophore (Cs I, 10 mmol/kg), bis(2-ethylhexyl) sebacate (DOS, 66 wt%) as plasticizer, and undecaiodinated closo-dodecacarborane (UIC, 4.1 mmol/kg) as ion exchanger exhibited superior performance with respect to selectivity over alkali and alkaline earth metal cations. The unbiased selectivity coefficients, log K-Cs,J(pot), for the principal interfering ions (J = K+, Na+, Ca2+ Mg2+) a and were determined to be - 2.9, - 4.7, - 8.5, and - 8.7, respectively. DOS-plasticized PVC electrodes containing Cs I and UIC were optimized for trace-level measurements, exhibiting a lower detection limit of 7.9 x 10(-9) M Cs+ (log aC(s,LDL) = - 8.1) in the presence of a 1 X 10(-5) M Na+ background. Ile utility of the optimized ISEs was demonstrated by determining the concentration of Cs+ in both drinking water and natural water samples.