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 $\rm{ {_{Cs,J}^{pot}}}$ , for the principal interfering ions (J=K + , Na + , Ca 2+ , and Mg 2+ ) 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 7.9×10 −9  M Cs + (log  a Cs,LDL =−8.1) in the presence of a 1×10 −5  M Na + background. The utility of the optimized ISEs was demonstrated by determining the concentration of Cs + in both drinking water and natural water samples.