Anion Selective Organotin-based ISEs

Meanwhile, the science of chemical sensors was developing fast. The technology of polymer-supported liquid membranes was already a mature science, as it was more than 15 years since it was first reported. The use of plasticized PVC allowed for the construction of membrane-based sensors with great ease, and gave sensor technology a new boost. It was the same basic technology that was subsequently used for the development of liquid-polymeric-based ISEs. 

The efforts of Simon s group to elucidate the mechanism and the selectivites of the organotin compounds continued. As shown in Table 3.4.1, a series of triorganotin compounds of the type RsSnY and RiR2SnY was evaluated with respect to their anion selectivities exhibited in solvent polymeric membranes. 

The study of such a large number of carriers allowed for the elucidation of the effect of both the amount of carrier in the membrane, as well as the effect of the ligand nature on the observed selectivities. It was thus concluded that the selectivity was influenced by the size of the constituent R groups, suggesting steric hindrance in the penta-coordination of the corresponding ionophores by analyte anions. 

The exceptional selectivity of this sensor allowed for the direct monitoring of salicylate in blood and serum with very good precision and accuracy. 

The fact that the organotin carriers were proven to be anion selective in their neutral form provided the required information for the development of an optical sensor. Based on the coextraction principle, an optical sensor membrane for the determination of chloride was described. For this, tri-n-octyltin chloride was used as the ionophore, and together with the appropriate pH sensitive chromoionophore, allowed for the development of an optical sensor system for the monitoring of chloride levels in blood and serum. 

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