Effect of Membrane Matrices on Performances of a Thiocyanate Ion-Selective Electrode Based on the (5,10,15,20-Tetraphenyl-porphyrinato)manganese(III) Anion Carrier

Abstract

Conductivities and emf responses of plasticized poly(vinyl chloride) (PVC) and 1, 2-dichloroethane membranes containing thiocyanato(5, 10, 15, 20-tetraphenylporphyrinato)manganese(III) (Mn(TPP)SCN) were studied. The specific conductivities of these two types of membranes were much lower than those of the corresponding membranes containing an anion exchanger, Capriquat. However, a clear difference can be seen in the contribution of the membrane matrices to the overall conductivities between the two types of membranes containing Mn(TPP)SCN; the plasticized PVC matrix greatly contributes to the overall conductivities, whereas the liquid membrane matrix contributes little. In the emf response, Mn(TPP)SCN in the conductometrically inert liquid membrane matrix ideally responds to thiocyanate, whereas it is not able to function ideally in the conductometrically active plasticized PVC matrix. As a possible mechanism for the non-ideal emf response of Mn(TPP)SCN in the plasticized PVC matrix, the failure in co-ion repulsion, which is induced by negatively charged impurities in PVC, is proposed.