Calix[4]arene derivatives incorporating pi-coordinate substituents such as allyl, benzyl, and propargyl groups were designed as soft neutral carriers for silver ion sensors. Most of all, tert-butylcalix[4]arene tetra(allyl ether) is an excellent neutral carrier for plasticized poly(vinyl chloride)-membrane silver ion-selective electrodes. The ion sensors showed high silver ion selectivity over alkali metal ions and also good selectivity against other soft metal ions such as lead and mercury(II) ions. The electrode potential response was as rapid as that for neutral-carrier-type alkali metal ion electrodes due to the soft interaction between pi-coordinate substituents and silver ion, which was elucidated by 1H NMR spectroscopy.
Dodecyl-16-crown-5, which contains one sulfur and four oxygen atoms, was synthesized and tested for its usefulness as a neutral carrier for Ag+-selective electrodes. The resulting ion-selective electrodes exhibited Nernstian response to Ag+ in a wide activity range. The ion selectivities against other heavy metal ions and alkali and alkaline-earth metal ions were quite excellent.
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