Ion-selective electrodes based on natural carboxylic polyether antibiotics

The response characteristics of poly (vinyl chloride) (PVC) matrix membrane ion-selective electrodes based on five natural carboxylic polyether antibiotics, ionomycin, lasalocid, monensin, nigericin, and salinomycin, were examined. These are characterized by a good response to divalent (alkaline-earth-metal) cations such as Ca²⁺and Ba²⁺. However, electrodes based on methyl esters, in which the carboxyl groups of the natural carboxylic polyethers are esterified, responded weakly to divaient cations. This indicated that the carboxyl group plays an important role in making a complex with the divalent cation in a lipophilic polymeric electrode membrane, which is significant for the electrode response to the divalent cation. Electrodes based on all the carboxylic polyethers except lasalocid show "bl-Nernstian response" for divalent cations. In order to explain this unusual response, Ion extraction and permeability measurements were carried out with lasalocid and monensin. The general relationship between electrode response and ion extraction or ion-ligand complexation is also discussed on the basis of the results obtained with lasalocid and monensin.