Cation permselectivity in the phase boundary of ionophore-incorporated solvent polymeric membranes as studied by Fourier transform infrared attenuated total reflection spectrometry

The behaviour of permselective membrane transport was studied by Fourier transform IR attenuated total refelction spectrometry and potential measurements for the solvent polymeric membranes incorporating several different ionophores. The stoichiometric ratios between the complexed cations and their corresponding counter anions in the phase boundary, 0.31-1.8 υm in depth, of the membrane were determined for each membrane made in contact with various primary ion solutions. When hydrophilic counter anions were used for the primary ion solutions, the IR spectra of the membrane were exclusively those of the complexed cations, and no IR-active anionic peak appeared. The intensity of the former peaks was found to be dependent on an added anionic site, carboxylated poly(vinyl chloride) and a derivative of tetraphenylborate, in the membranes, and also on the penetration depths of the IR beams used. In contrast, when a hydrophobic counter anion SCN^-, was used for the primary ion solutions, the spectra from both the complexed cation and corresponding counter anion were seen, of which the stoichiometric ratios changed depending on the concetrations of primary ion salts, and on the coexistence of a derivative of tetraphenylborate in the membrane. The results are discussed in terms of the extent of cation permselectivity and its relevance to the potential of ionophore-incorporated liquid membrane ion-selective electrodes.