Abstract: The invention relates to a membrane that is selective for anions, particularly phosphate, comprising an ionophore based on a uranyl complex with the annexed general formula, whereinA, B, C, D=RA+B+C+D=(C.sub.5 -C.sub.7) aryl, (C.sub.5 -C.sub.7) cycloalkyl,(C.sub.1 -C.sub.30) alkyl (C.sub.5 -C.sub.10) aryl, (C.sub.1 -C.sub.30) alkyl (C.sub.5 -C.sub.10) cycloalkyl,E+E', G+G'=aryl, such as phenyl and naphthyl, or aryl substituted with a substituent (C.sub.1 -C.sub.30) alkoxy, or aryl substituted with the individual substituent or the substituent joined by ring closure K and/or K--CONH--L, whereinK, L=H --R--(CH.sub.2).sub.m --, --R--(CH.sub.2).sub.m --R, --X--(CH.sub.2).sub.m --, --X(CH.sub.2).sub.m --R, --X--(CH.sub.2).sub.m --X, --X(CH.sub.2).sub.m --X--R, --RX(CH.sub.2).sub.m --, --RX(CH.sub.2).sub.m --XR, --X--(R--X).sub.n --,wherein X=O, S; m= 0-10 and n= 0-10R=(C.sub.1 -C.sub.30) alkyl, (C.sub.5 -C.sub.10) aryl, (C.sub.5 -C.sub.10) cycloalkyl, (C.sub.1 -C.sub.30) alkyl (C.sub.5 -C.sub.10) aryl, (C.sub.

Abstract: An ionophore according to the general formula I wherein the substituents are chosen such that the ionophore is either also polymerized in the matrix of a membrane selective for metal ions or interwoven therewith. Thus obtained is a membrane having a long useful life for use in diverse sensors such as ISFET, ion-selective electrode, and the like.