Charged impurities of plasticizer used for ion-selective electrode and taste sensor

Receptor membranes used in ion-selective electrodes and a recently developed taste sensor are made from polyvinyl chloride (PVC) and plasticizer mixed with some ion carriers or lipids. A popular plasticizer material is dioctyl phenylphosphonate (DOPP). It is known that the membrane made of PVC and DOPP shows selectivity to cations; however, its mechanism has not been clarified because this membrane should have no negative electric charge to cause cation selectivity. In this study, identification of the charged impurity, phenylphosphonic acid monooctyl ester, from commercially available DOPP was made using frit fast atom bombardment (FRIT-FAB). Response characteristics of three kinds of PVC membranes containing different plasticizers (DOPP, 2-nitrophenyl octyl ether, 1-tetradecanol) to KCI were also shown to be much different. These results will contribute to the fabrication of receptor membranes.