Abstract: An ion-selective polymeric membrane for an electrochemical sensor for use in analytical chemistry, comprisinga) a supporting matrix e.g. of PVC, andb) an ionophore selected from calixarene or oxacalixarene derivatives of the formula IV ##STR1## wherein n+m=3-8;m=0-8;n=0-8;a, which may be the same or different on each aryl group, is 0 or 1;R.sup.2 is alkyl, aryl, alkaryl, alkoxy, alkoxyalkoxy, aryloxy, alkaryloxy, alicyclic, alkylthio, arylthio, alkarylthio, or a substituted derivative thereof;R.sup.3 is --H, alkyl or alkenyl;X is --OH or a group containing an acrylate or methacrylate functional group;provided that when X is --OH, n is at least 1/2(n+m);and provided that when m=0, n=4, a=0 and R.sup.3 is alkyl or allyl, R.sup.2 is not alkoxy having 4 or more carbon atoms in the alkyl group;and provided that when m=0, n=4, a=0 and R.sup.3 is t-butyl, R.sup.2 is not methoxy or ethoxy;or of the formula V ##STR2## wherein R.sup.