The invention pertains to a novel ionophore having the general structure (I): wherein R1, R2, R3 and R4 are independently straight or branched chain alkyl having 4 to 12 carbon atoms or the alkyl groups may optionally contain a cycloalkly group having 3 to 8 carbon atoms or R1 and R2 or R3 and R4 together with N to which they are attached, can form a ring having 5 to 8 carbon atoms. This ionophore has increased selectivity for carbonate ions over other ions, especially salicylate. The invention includes membranes containing effective amounts of the novel ionophores and -sensors containing these membranes.