Development of a fluorescent optode membrane for sodium ion based on the calix[4]arene and tetraphenylporphine

A fluorescent optode membrane for sodium ion that works on the basis of a cation-exchange mechanism has been developed. The plasticized poly(vinyl chloride) (PVC) membrane incorporating sodium-selective ionophore (4-tert-butylcalix[4]arene tetraacetic acid tetraethyl ester), acidic fluorescent pH indicator (5,10,15,20-tetraphenylporphine, TPP) and a lipophilic anionic site (potassium tetrakis(4-chlorophenyl)borate) was used as the sensing device, which exhibits the theoretically expected fluorescent response to sodium ion. The selectivity, response time, reproducibility and lifetime of the optode membrane were discussed.