METALLOPORPHYRIN DERIVATIVES AS NEUTRAL CARRIERS FOR PVC MEMBRANE ELECTRODES

The anion-sensitive membrane electrodes based on lipophilic metalloporphyrin derivatives (FeTPP)(2)O show similar anti-Hofmeister selectivity sequence: SCN- > I- > ClO4- > NO2- > Br- > Cl- > NO3-. The electrode with an optimum membrane composition has a linear response for SCN- between 10(-6) and 10(-1) mol/L, with a slope of 53.0 mV/p-SCN- (25 degrees C). The origin of the anti-Hofmeister response characteristics has been discussed in view of the coordination chemistry of the metalloporphyrins. The interaction mechanism between (FeTPP)(2)O and SCN- is studied by UV/vis and IR spectroscopy. The transfer process of SCN- across the membrane interface is investigated by sc impedance measurements.