Lipophilic neutral surfactants of the sugar alkyl ester type are experimentally observed to substantially increase the ion transfer impedance between an aqueous solution and ion-selective electrode membranes made from plasticized PVC with neutral carrier. The magnitude of the effect depends considerably on the molecular structure and on the concentration of the surfactant. Statistical thermodynamic simulation of the experimental system agrees qualitatively with the experimental observations. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.