TD19C6 is an ammonium ion selective ionophore. It is difficult to separate ammonium ion and potassium ion because they are close in ion size. The selectivity of TD19C6 for ammonium ion is about 10 times that of potassium ion, which is nearly the same selectivity of nonactin.
1. K. Suzuki, et al., Design and Synthesis of a More Highly Selective Ammonium Ionophore Than Nonactin and Its Application as an Ion-Sensing Component for an Ion-Selective Electrode. Anal Chem. 2000;72:2200-2205.