Journal of Electroanalytical Chemistry, Vol.833, 498-504, 2019
The application of germanium(IV)-porphyrins as fluoride-selective ionophores for polymeric membrane electrodes
In this work, the possibility of using Ge(IV)-porphyrins as anion-selective ionophores for potentiometric measurements was tested. Conducted experiments shown that polymeric membranes doped with these compounds exhibit high selectivity towards fluoride anion. Ge(IV)-tetraphenylporphyrin was initially used as a ionophore, however rapid crystallization of this compound in the membrane phase was observed. To mitigate this problem, more lipophilic derivative with tert-butyl groups was synthesized and doped into polymeric membranes. Ge(IV)-porphyrins were shown to work according to charged carrier mechanism, requiring 10 to 20 mol% of borate additive for optimal selectivity. The anti-Hofmeister selectivity pattern: F- > SCN- > ClO4- > Br- > NO3- > Cl- was observed for membranes containing Ge(IV)-porphyrin and anionic additive. Electrodes with these membranes responded to changes in fluoride concentration in fast and near-Nernstian fashion. Strong interaction between fluoride ion and tested ionophores resulted in the inversion of the F- calibration curve at high concentration, which was especially pronounced for electrodes with membranes containing higher amounts of borate additive.